title:
Naturalness Lowers the Upper Bound on the Lightest Higgs Boson Mass in
  Supersymmetry

abstract:
  We quantify the extent to which naturalness is lost as experimental lower
bounds on the Higgs boson mass increase, and we compute the natural upper bound
on the lightest supersymmetric Higgs boson mass. We find that it would be
unnatural for the mass of the lightest supersymmetric Higgs boson to saturate
it's maximal upper bound. In the absence of significant fine-tuning, the
lightest Higgs boson mass should lie below $120$ GeV, and in the most natural
cases it should be lighter than $108$ GeV. For modest $tan \beta$, these bounds
are significantly lower. Our results imply that a failure to observe a light
Higgs boson in pre-LHC experiments could provide a serious challenge to the
principal motivation for weak-scale supersymmetry.


title: Cosmological abundances of right-handed Dirac neutrinos

abstract:
  The equilibration of the right-helicity states $\nu_+$ of light
Dirac-neutrinos is discussed. I point out that the $\nu_+$ production rate is
enhanced by weak gauge boson pole effects so that the right-helicity component
of $\nu_\tau$ is brought into equilibrium at $T\simeq 10$ GeV independently of
the initial abundance, provided $m_{\nu_{\tau}}\gsim 10$ keV. Neutrino spin
flip in primordial magnetic fields and the resulting bound on $\mu_\nu$ is also
discussed.


title: Light Quark Effective Theory

abstract:
  Lecture Notes, Summer School on Effective Theories and Fundamental
Interactions, Erice, 1996. The application of effective field theory methods to
the low energy structure of QCD is discussed. I emphasize the universal
structure of the corresponding effective Lagrangian and then discuss the
physics of the effective coupling constants. The implications of the effective
theory for the masses of the light quarks are analyzed in some detail.


title: Phonons as Goldstone Bosons

abstract:
  The implications of the hidden, spontaneously broken symmetry for the
properties of the sound waves of a solid are analyzed. Although the discussion
does not go beyond standard wisdom, it presents some of the known results from
a different perspective. In particular, I argue that, as a consequence of the
hidden symmetry, the equations of motion for a sound wave necessarily contain
nonlinear terms, describing phonon-phonon scattering and emphasize the analogy
with the low energy theorems for pion-pion scattering.


title: Light Quark Masses

abstract:
  Lecture Notes, Summer School on Masses of Fundamental Particles, Cargese,
1996. In the first part, some qualitative aspects the mass pattern are
discussed, concerning the breaking of isospin and eightfold way symmetries. The
second part deals with the chiral perturbation theory results for the masses of
the pseudoscalar octet, which lead to very stringent constraints for the
relative size of the light quark masses.


title:
CC10 at ${\cal O}(\alpha_s )$: QCD corrections to $e^+ e^- \to \mu^-
  \bar \nu_\mu u \bar d$ at LEP2 and the Next Linear Collider

abstract:
  QCD one-loop corrections to the semileptonic process $e^+ e^- \to \mu^- \bar
\nu_\mu u \bar d$ are computed. We compare the exact calculation with a
``naive'' approach to strong radiative corrections which has been widely used
in the literature and discuss the phenomenological relevance of QCD
contributions for LEP2 and NLC physics.


title: QCD Sum Rules for Heavy Baryons at Next-to-Leading Order in alpha_s

abstract:
  We derive QCD sum rules for heavy baryons at leading order in $1/m_Q$ and at
next-to-leading order in $\alpha_s$. The calculation involves the evaluation of
four different perturbative three-loop diagrams which determine the
$\alpha_s$-corrections to the Wilson coefficients of the leading term in the
Operator Product Expansion (OPE). From the sum rules we obtain estimates for
the masses and the residues of the heavy baryons $\Lambda_Q$ and $\Sigma_Q$.
The perturbative $O(\alpha_s)$ corrections to the leading order spectral
function amount to about $100%$, and they shift the calculated values for the
baryon masses slightly upward. The residues are shifted upward by about
$20-50%$. For the bound state energy $\bar\Lambda$ given by the difference of
the heavy baryon mass and the pole mass of the heavy quark $m_Q$ we obtain
$m_{\Lambda_Q}-m_Q=780 MeV$ and $m_{\Sigma_Q}-m_Q=950 MeV$. For the residues we
find $|F_\Lambda|=0.028 GeV^3$ and $|F_\Sigma|=0.039 GeV^3$.


title: Charmonium Suppression in Nuclear Collisions

abstract:
  Measurements of $\psi$ and $\psi'$ production from experiment NA50 at the
CERN SPS are compared to predictions based on a hadronic model of charmonium
suppression by Vogt and myself. Data on centrality dependence and total cross
sections are in good accord with our predictions. Uncertainties in theoretical
quanities such as NA50's $L$ parameter are discussed.


title: The Classical Analogue of CP-violation

abstract:
  The phenomenological features of the mixing in the neutral pseudoscalar
mesons K0-K0bar can be illustrated in the classical framework of mechanics and
by means of electromagnetic coupled circuits. The time-reversed not-invariant
processes and the related phenomenon of CP-nonconservation can be induced by
dissipative effects which yield a not vanishing imaginary part for the relevant
Hamiltonian. Thus, two coupled dissipative oscillators can resemble the
peculiar asymmetries which are so common in the realm of high energy particle
physics.


title:
Chargino Production in Different Supergravity Models and the Effect of
  the Tadpoles

abstract:
  If the lightest chargino is discovered at LEP2, the measurement of its mass
and cross section together with the mass of the lightest neutralino, enables
the determination of the parameters that define the theory and the entire
supersymmetric and Higgs spectrum. Within this context, we: (i) study the
effect of the one--loop tadpoles in the minimization condition of the Higgs
potential, by comparing the RGE--improved Higgs potential approximation with
the calculation of the minimum including the effect of the one--loop tadpoles,
and (ii) compare the prediction of two different supergravity models, namely,
the model based on $B=2m_0$ and motivated by the solution of the
$\mu$--problem, and the minimal supergravity model, based on $A=B+m_0$.


title: Multiplicity Distributions and Fluctuations in the Discrete QCD Model

abstract:
  Results are presented from calculations carried out in the discrete QCD
model, concerning multiplicity distributions in rapidity intervals and
fluctuations.


title: The One-loop QCD Corrections for $\gamma^* to Q\bar Q q\bar q$

abstract:
  We calculate the one-loop QCD corrections for the decay of an off-shell
vector boson with vector couplings into two pairs of quarks of equal or unequal
flavours keeping all orders in the number of colours. These matrix elements are
relevant for the calculation of the next-to-leading order ${\cal
O}(\alpha_s^3)$ corrections to four jet production in electron-positron
annihilation, the production of a gauge boson accompanied by two jets in
hadron-hadron collisions and three jet production in deep inelastic scattering.
We use standard techniques for computing the interference of one-loop and tree
level Feynman diagrams, but organise the results in terms of combinations of
scalar loop integrals that are finite in the limit of vanishing Gram
determinants and are therefore numerically stable.


title: Looking for a Light Higgs Particle at Present and Future Colliders

abstract:
  Present data do not rule out the light neutral Higgs particle $h$ or $A$ with
mass below 40--50 GeV in the framework of the general 2HDM ("Model II"). The
recent limits from LEP I on the parameters of the model, based on the Bjorken
process $Z \to Z h$, Higgs pair production $Z \to A h$ and the Yukawa process
$Z \to f {\bar f} A$ ($f= b$ quark or $\tau$ lepton) are presented. Including
limits on Higgs bosons masses from LEP I data additional constraints on the
allowed value for $ tan \beta$ for mass below 2 GeV, can be obtained from the
existing $(g-2)_{\mu}$ data. The improvement in the accuracy by factor 20 in
the forthcoming $(g-2)_{\mu}$ experiment E821 may lead to more stringent limits
on mass of neutral Higgs boson up to 30 GeV, or even higher if the mass
difference between $h$ and $A$ is larger than $M_Z$. The exclusion/discovery
potential of the gluon-gluon fusion in $ep$ collision at HERA is also
discussed. Already for a luminosity $ L_{ep} =25 pb^{-1}$ this measurement may
lead to more stringent limits on $ tan \beta$ for the mass range 5-15 GeV,
especially for the pseudoscalar case. In addition the possible search for very
light Higgs particle in $\gamma \gamma$ fusion at low energy (10 GeV) LC is
described. It may improve bounds considerably compared to the present limits
for mass around between 1.5 and 8 GeV assuming the luminosity $10 fb^{-1}$.


title: Flavor Oscillations in Field Theory

abstract:
  Neutrino flavor oscillations are discussed in terms of two coupled Dirac
fields. The interacting Lagrangian is diagonalized to obtain the exact
eigenvalues and eigenfunctions. Flavor wave functions are then derived directly
from the quantized neutrino fields. Probability density obtained by squaring
these wave functions upon taking into account the neutrino chirality are in
agreement with the standard neutrino oscillation probabilities.


title: Higgs Search at HERA

abstract:
  Present data do not rule out a light neutral Higgs particle with mass below
40--50 GeV in the framework of 2HDM with $ tan \beta \sim $ 20-30. The
promising possibility of searching for a light Higgs particle in such a
scenario in photoproduction at HERA collider is discussed. For the MSSM there
is only a very small chance to observe the Higgs sector, and only for limited
mass range $\sim$ 45-50 GeV and with large $ tan \beta$.


title: The Heavy-Flavour Contribution to Proton Structure

abstract:
  We present theoretical and experimental considerations pertaining to deeply
inelastic heavy-flavour production at HERA. The various theoretical
uncertainties in the cross section calculation are discussed. Cuts are imposed
to determine the fraction of charm production accessible to the detectors. The
production of charm at asymptotic $Q^2$ and bottom production are also covered.
Experimental aspects include current charm production data analysis and
prospects for future analyses including anticipated high precision and
distinguishing photon-gluon fusion charm events from excitation from the charm
parton density. The feasibility of measuring $F_2^{b\overline b}(x,Q^2)$ is
investigated.


title: Axial-vector meson mixing in orthocharmonium decays

abstract:
  The new BES measurement on the two-body decays of J/psi and psi' into an
axial-vector meson and a pseudoscalar meson is analyzed with the axial-K mixing
including the one-photon annihilation contribution. A somewhat puzzling pattern
of the K_1^+ K^- decay channels can be understood with no tight constraint on
the mixing angle. The branching fractions of the K_1^0 K-bar^0 channels will be
the cleanest source of information to determine the mixing angle from the 1^+
0^- decays of J/psi and psi'.


title: Low-Energy Signatures of Semi-perturbative Unification

abstract:
  We consider the low-energy signatures of, and high-energy motivations for,
scenarios of semi-perturbative gauge coupling unification. Such scenarios can
leave striking imprints on the low-energy sparticle spectrum, including novel
gaugino mass ratios (including $M_2/M_1\approx1$), substantial compression of
the intra-generational squark-to-slepton mass ratios, and an overall lifting of
scalar masses relative to the gauginos. We also demonstrate that the
unification scale can be raised to $M_X \approx 4\times10^{17}$ GeV while still
in the perturbative regime -- close to the 1-loop heterotic string scale. We
employ a 3-loop calculation of the running of the gauge couplings as a test of
the perturbativity of the high-scale theory.


title: The hot baryon violation rate is $O(\alpha_W^5 T^4)$

abstract:
  The rate per unit volume for anomalous electroweak baryon number violation at
high temperatures, in the symmetric phase, has been estimated in the literature
to be $O(\alpha_W^4 T^4)$ based on simple scaling arguments. We argue that
damping effects in the plasma suppress the rate by an extra power of $\alpha_W$
to give $O(\alpha_W^5 T^4)$. We show how to understand this effect in a variety
of ways ranging from an effective description of the long-distance modes
responsible for baryon number violation, to a microscopic picture of the
short-distance modes responsible for damping. In particular, we resolve an old
controversy as to whether damping effects are relevant. Finally, we argue that
similar damping effects should occur in numerical simulations of the rate in
classical thermal field theory on a spatial lattice, and we point out a
potential problem with simulations in the literature that have not found such
an effect.


title: Probing the Electroweak Symmetry Breaking Sector with the Top Quark

abstract:
  A study on effective anomalous interactions up to dimension 5 of the top
quark with the electroweak gauge bosons is made in the non-linear Chiral
Lagrangian approach. Bounds on the anomalous dimension four terms are obtained
from their contribution to low energy data. Also, the potential contribution to
the production of top quarks at hadron colliders (the Tevatron and the LHC) and
the electron Linear Collider from both dimension 4 and 5 operators is analysed.


title: On the hadronic production of $B_c$ and $B_c^*$ mesons

abstract:
  With respect to the two theoretical approaches for estimating the hadronic
productions of the mesons $B_c$ and $B_c^*$: the full $\alpha_s^4$ calculation
and the fragmentation approximation, with a thorough comparative study a quite
remarkable conclusion may be drawn. In hadronic collisions the condition for
the applicability of the fragmentation approximation is the transverse momentum
$P_T$ of the produced $B_c$ and $B_c^*$ being much greater than the meson
masses, and the higher the energy of the relevant subprocess the higher the
$P_T$ is requested. The mechanisms for the productions are also clarified. In
order to show the resultant differences of the two approaches, newly introduced
distribution of the fraction of the $B_c$ (or $B_c^*$) meson energy (a
measurable observable) in the center of mass of the subprocess is emphasized.


title:
Semileptonic $B \to \rho$ and $B \to \pi$ Decays: Lattice and Dispersive
  Constraints

abstract:
  I present two recent pieces of work on semileptonic $B \to \pi, \rho$ decays
where it is shown how lattice QCD calculations can be used to test heavy-quark
symmetry and determine phenomenologically relevant quantities despite the
limits on these calculations' kinematical reach. The study of semileptonic $B
\to \rho$ decays was performed with the UKQCD Collaboration.


title: Future Diffractive Structure Function Measurements at HERA

abstract:
  The purposes and possibilities of future diffractive structure function
measurements at HERA are presented. A review of the current range and accuracy
of the measurement of $F_2^{D(3)}(\beta, x_p, Q^2)$ is presented and an
estimate of the precision of future measurements is given. A feasibility study
is performed on the measurement of the structure functions $F_2^{D(4)}(\beta,
x_p, Q^2, t)$, $F_{2 charm}^{D}$, $R^{D(3)}$, $R^{D(4)}$ and $F_L^{p}$.
Included in this study are estimates of the integrated luminosity required, the
analysis techniques to be employed and values of systematic error that could be
expected.


title: A String-inspired Ansatz for Quark Masses and Mixing

abstract:
  We propose a simple but realistic pattern of quark mass matrices at the
string scale, which can be derived from orbifold models of superstring theory
with no use of gauge symmetries. This pattern is left-right symmetric and
preserves the structural parallelism between up and down quark sectors. Its
phenomenological consequences on flavor mixing and $CP$ violation are
confronted with current experiments at the weak scale by use of the
renormalization-group equations in the framework of the minimal supersymmetric
standard model. We find that good agreement is achievable without fine-tuning.


title: Bileptons: Present Limits and Future Prospects

abstract:
  We define bileptons to be bosons coupling to a pair of leptons and construct
the most general dimension four lagrangian involving scalar and vector
bileptons. We concentrate on fields with lepton number 2, and derive model
independent bounds on their masses and couplings from low-energy data. In
addition, we study their signals in high energy experiments and forecast the
discovery potential of future colliders.


title: Implications of the Electroweak Precision Data: a 1996 Update

abstract:
  The most reliable prediction for the Higgs-boson mass, M_H, is obtained in a
fit to the leptonic Z-resonance observables Gamma_l and swbar^2 combined with
the W-boson mass, M_W, and top-quark mass, m_t, measurements. The corresponding
bounds on M_H are independent of potential uncertainties related to R_b, R_c,
and alpha_s(M_Z^2), and they are not significantly further improved by
including also the experimental information on the inclusive (hadronic and
total) Z-boson decays. At the 1sigma level, we obtain M_H<360GeV using
swbar^2(LEP+SLD) and M_H<540GeV using swbar^2(LEP). Our analysis in terms of
effective parameters confirms previous conclusions with increased accuracy. In
the mass parameter, Delta x, and the mixing parameter, epsilon, pure fermion
loops are sufficient, while for the coupling parameter, Delta y,
(M_H-insensitive) bosonic contributions are essential for consistency with
experiment, thus providing indirect empirical evidence for the non-Abelian
structure of the theory.


title:
Future Precision Measurements $F_2(x,Q^2)$, $\alpha_S(Q^2)$ and
  $xg(x,Q^2)$ at HERA

abstract:
  The results are presented of a study of the accuracy one may achieve at HERA
in measuring the strong coupling constant $\alpha_s$ and the gluon distribution
$xg(x,Q^{2})$ using future data of the structure function $F_{2}(x,Q^{2})$
which are estimated to be accurate at the few % level over the full accessible
kinematic region down to $x \simeq 10^{-5}$ and up to $Q^{2} \simeq 50000
GeV^{2}$. The analysis includes simulated proton and deuteron data, and the
effect of combining HERA data with fixed target data is discussed.


title: Vector Meson Production at HERA

abstract:
  We show that the lowest-order QCD calculation in a simple model of elastic
vector-meson production does reproduce correctly the ratios of cross sections
for rho, phi and J/psi, both in photoproduction and in high-Q2 quasi-elastic
scattering. The dependence of the slopes on the mass of the vector meson is
reproduced as well. We examine the lower-energy data, and find that the energy
dependence of the cross section does not depend on Q2, but may depend on the
vector-meson mass.


title: Nonhermitean Random Matrix Models : a Free Random Variable Approach

abstract:
  Using the standard concepts of free random variables, we show that for a
large class of nonhermitean random matrix models, the support of the eigenvalue
distribution follows from their hermitean analogs using a conformal
transformation. We also extend the concepts of free random variables to the
class of nonhermitean matrices, and apply them to the models discussed by
Ginibre-Girko (elliptic ensemble) and Mahaux-Weidenm\"uller (chaotic resonance
scattering).

categories: hep-ph chao-dyn cond-mat hep-th nlin.CD nucl-th


title:
The Modified Intrinsic Charm Model And J/Psi Production in Hadronic
  Collisions

abstract:
  Using the statistical approach additional light partons have been introduced
in the Intrinsic Charm model. Explicit expressions are obtained for charmed and
light quark distributions. A comparison is made with standard IC model
predictions. It is shown that such a modification of the IC model leads to
better agreement with the $pN$ and $\pi N$ data on $\JP$ production at low
energies and allows to avoid a contradiction to experimental data at high
energy.


title: Spontaneous Leptogenesis

abstract:
  I propose a new mechanism for baryogenesis, in which the out-of-equilibrium
condition is not neccessary. When the electroweak symmetry is broken
spontaneously, left-handed neutrinos may get Majorana masses containing
$CP-$violating phases. This induces a lepton asymmetry spontaneously, which is
then converted to a baryon asymmetry in the presence of the sphaleron field.


title: A Possible Explanation of the Excess Jet Production at Large E_T

abstract:
  We demonstrate that the significant discrepancy between the previous
predictions of the conventional QCD and the CDF inclusive jet production data
could be an indication that the behaviour of the Callan-Symanzik \beta function
in QCD corresponds to it having an ultraviolet finite fixed point.


title: Baryon moments in a QCD-based model

abstract:
  We have analyzed the theory of the baryon magnetic moments in the
approximate) QCD setting suggested by Brambilla et al. By modifying their
derivation of the $qqq$ interaction and wave equation for baryons, we derived
expressions for the baryon moments in terms of the underlying quark moments,
including the first corrections associated with the binding of the quarks in
baryons. The results, which hold in the ``quenched approximation'' in which the
contributions of virtual quark pairs are neglected, fail to describe the
measured moments, with typical errors on the order of 7%. We conclude from our
analysis that the quenched approximation is at fault, and that the baryon
moments give a sensitive test of that standard approximation in the lattice and
analytic approaches to QCD.


title: Cabibbo Mixing and the Search for CP Violation

abstract:
  We examine certain extensions of the standard model in which $CP$ violation
is spontaneous and the strong $CP$ problem is resolved. In these models, the $3
\times 3$ quark mixing matrix is neither real nor unitary. However, to a
precision of 0.1%, it is real and orthogonal. There are no readily observable
$CP$-violating effects besides those in the neutral kaon system.


title: Protecting the Baryon Asymmetry in Theories with R-parity Violation

abstract:
  We propose a mechanism for hiding the primordial baryon asymmetry from
interactions that could wash it out. It requires the introduction of a baryon
number carrying singlet which is in equilibrium in the early universe and
shares any existing baryon asymmetry. It decouples from the Standard Model
particles before all the interactions required to wash out the asymmetry are in
equilibrium ($T \simeq 10$ TeV), and decays after the electroweak phase
transition, but before nucleosynthesis. This mechanism can conserve a baryon
asymmetry in models (a) with $B-L = 0$, such as many $SU(5)$ GUTs, or (b) with
$B-L$ violating interactions in thermal equilibrium, such as SUSY with broken
$R$-parity. As a result, cosmological constraints on $R$-parity violating
operators are relaxed considerably.


title:
Determination of flavor asymmetry for $\Sigma^{\pm}$ by the Drell-Yan
  process

abstract:
  Flavor asymmetries for the valence and sea quarks of the $\Sigma^{\pm}$ can
be obtained from Drell-Yan experiments using charged hyperon beams on proton
and deuteron targets. A large, measurable difference in sea quark asymmetries
is predicted between SU(3) and pseudoscalar meson models. The latter predict
that in $\Sigma^{+}$, $\bar{u}/\bar{d} \leq 1/2$, whereas the former predict
$\bar{u}/\bar{d} \approx 4/3$. Estimates of valence quark asymmetries based on
quark models also show large deviations from SU(3) predictions, which should be
measurable.


title:
Monopole Dominance for Dynamical Chiral-Symmetry Breaking in the Dual
  Ginzburg-Landau Theory

abstract:
  Using the effective potential formalism, we study dynamical chiral symmetry
breaking (D$\chi$SB) in the dual Ginzburg-Landau (DGL) theory, where the color
confinement is brought by monopole condensation. The effective potential as a
function of infrared quark mass is found to have double-well structure, which
leads to spontaneous breaking of chiral symmetry. To examine the role of
confinement, we divide the effective potential into the confinement part and
others, which correspond to the confinement term and other (Yukawa, Coulomb)
terms of the gluon propagator in the DGL theory. It is found that the
confinement part gives the dominating contribution to the \dcsb, which is
regarded as monopole dominance for D$\chi$SB.


title: Prospects for Quarkonium Physics at HERA

abstract:
  We work out and review prospects for future quarkonium physics at HERA. We
focus on the impact of color-octet contributions and discuss how measurements
at HERA can be used to test the picture of quarkonium production as developed
in the context of the NRQCD factorization approach.


title:
Lattice-Constrained Dispersive Bounds for $\bar B^0 \to \pi^+ l^-
  \bar\nu$ Decays

abstract:
  I present a recent piece of work on semileptonic $B \to \pi$ decays in which
lattice results and kinematical and dispersive constraints are combined to
obtain model-independent bounds on the relevant form factors and rates.


title: CP Violation in Semileptonic $\tau$ Decays with Unpolarized Beams

abstract:
  CP violating signals in semileptonic $\tau$ decays are studied. These can be
observed in decays of unpolarized single $\tau$'s even if their rest frame
cannot be reconstructed. No beam polarization is required. The importance of
the two meson channel, in particular the $K\pi$ final state is emphasized.


title: Form factors for rare decays $B\to(\pi,\rho,K,K^*)l^+l^-$ in quark model

abstract:
  Hadronic matrix elements of the vector, axial-vector and tensor currents
relevant for exclusive rare decays $B\to(\pi,\rho,K,K^*)\,l^+l^-$ induced by
the quark transition $b\to d,s$ are analysed using dispersion formulation of
the light-cone constituent quark model. The form factors in the decay region
are expressed as relativistic double spectral representations through the
light-cone wave functions of the initial and final mesons. These form factors
are shown to have the correct scaling properties in the limit of heavy-to-heavy
and heavy-to-light quark transitions in accordance with QCD. The dependence on
the quark-model parameters is studied.


title: J/psi Spin Asymmetries in the Colour-Octet Model

abstract:
  We investigate the pattern of asymmetries in the colour-octet model for
inclusive production of charmonium with polarised initial state hadrons and
photons. We find that singly polarised asymmetries vanish. The double polarised
asymmetry for J/psi involves a new combination of long-distance matrix element.
We also investigate the asymmetries for eta_c, chi_c and Upsilon production.
The asymmetries distinguish well between different models of charmonium
production.


title:
Finite Temperature SD Equation for Chiral Symmetry Restoration in Dual
  Ginzburg-Landau Theory

abstract:
  We study the chiral phase transition at $T\neq 0$ in the dual Ginzburg-Landau
theory using the Schwinger-Dyson (SD) equation. In order to solve the SD
equation at $T\neq 0$, we provide a new ansatz for the quark self-energy in the
imaginary-time formalism. The recovery of the chiral symmetry is found at
$T_{_{C}}\sim 100 MeV$ with realistic parameters, which are set by reproducing
the values of the string tension $\sqrt{\sigma}\simeq 0.44 GeV$ and the chiral
condensate $< {\bar q}q > \simeq -(250 MeV}^{3}$ at $T=0$.


title:
Thermodynamics of Hidden Sector Gaugino Condensation in the Expanding
  Universe

abstract:
  This work examines the confining-deconfining phase transition in a hidden
Yang Mills sector with scale $\Lambda \sim 10^{14}$ GeV appropriate to dilaton
stabilization and SUSY-breaking via formation of a gaugino consensate. If the
transition is assumed to take place through homogenous nucleation, then under
reasonable assumptions it is found that a critical bubble, formed at a
temperature which provides enough supercooling, is not large enough to
accommodate an adequate number $(\gsim 100)$ of quanta of the confined phase
(`hidden hadrons') to allow a consistent thermodynamic description. Thus, a
first order transition in the hidden sector may not be possible in the
expanding universe.


title: Gauss's law and gauge-invariant operators and states in QCD

abstract:
  In this work, we prove a previously published conjecture that a prescription
we gave for constructing states that implement Gauss's law for `pure glue' QCD
is correct. We also construct a unitary transformation that extends this
prescription so that it produces additional states that implement Gauss's law
for QCD with quarks as well as gluons. Furthermore, we use the mathematical
apparatus developed in the course of this work to construct gauge-invariant
spinor (quark) and gauge (gluon) field operators. We adapt this SU(3)
construction for the SU(2) Yang-Mills case, and we consider the dynamical
implications of these developments.


title: How to Search for a Light Stop at the Tevatron

abstract:
  We describe a method for searching for a light stop squark
[M(stop)+M(LSP)<M(t)] at the Fermilab Tevatron. Traditional searches rely upon
stringent background-reducing cuts which, unfortunately, leave very few signal
events given the present data set. To avoid this difficulty, we suggest using a
milder set of cuts, combined with a ``superweight,'' whose purpose is to
discriminate between signal and background. The superweight consists of a sum
of terms (each of which are either zero or one) assigned event-by-event
depending upon the values of various observables. By construction, the
superweight ``large'' for the signal and ``small'' for the background. We apply
this method to the detection of stops coming from top decay. It is
straightforward to adapt our method to other processes.


title: Neutrino Oscillations from Dirac and Majorana Masses

abstract:
  We present a scenario of neutrino masses and mixing angles. Each generation
includes a sterile right handed neutrino in addition to the usual left handed
one. We assume a hierarchy in their Dirac masses similar to, but much larger
than the hierarchies in the quarks and charged leptons. In addition, we include
a Majorana mass term for the sterile neutrinos only. These assumptions prove
sufficient to accomodate scales of mass differences and mixing angles
consistent with all existing neutrino oscillation data.


title: The Dynamical Nonabelian Two-Form: BRST Quantization

abstract:
  When an antisymmetric tensor potential is coupled to the field strength of a
gauge field via a $B\wedge F$ coupling and a kinetic term for $B$ is included,
the gauge field develops an effective mass. The theory can be made invariant
under a non-abelian vector gauge symmetry by introducing an auxiliary vector
field. The covariant quantization of this theory requires ghosts for ghosts.
The resultant theory including gauge fixing and ghost terms is BRST-invariant
by construction, and therefore unitary. The construction of the BRST-invariant
action is given for both abelian and non-abelian models of mass generation.


title:
Constraints on supersymmetric soft phases from renormalization group
  relations

abstract:
  By using relations derived from renormalization group equations (RGEs), we
find that strong indirect constraints can be placed on the top squark mixing
phase in At from the electric dipole moment of the neutron (dn). Since mtop is
large, any GUT-scale phase in At feeds into other weak scale phases through
RGEs, which in turn contribute to dn. Thus CP-violating effects due to a
weak-scale At are strongly constrained. We find that |Im At(mz)| must be
smaller than or of order |Im B(mz)|, making the electric dipole moment of the
top quark unobservably small in most models. Quantitative estimates of the
contributions to dn from Au, Ad and B show that substantial fine-tuning is
still required to satisfy the experimental bound on dn. While the low energy
phases of the A's are not as strongly constrained as the phase of B(mz), we
note that the phase of a universal A(GUT) induces large contributions in the
phase of B(mz) through RGEs, and is thus still strongly constrained in most
models with squark masses below a TeV.


title: $b \to s l \bar l $ in the minimal supergravity model

abstract:
  The $b \rightarrow s l^+ l^-$ process is studied in the minimal supergravity
model in detail. Taking account of the long distance contributions from the
$c\overline{c}$ resonances, we calculate the branching ratio and the lepton
forward-backward asymmetry in this model. We find that there is a strong
correlation between the branching ratios of $b \rightarrow s \gamma$ and $b
\rightarrow s l^+ l^-$ processes and that the interference effect can change
the $b \rightarrow s l^+ l^-$ branching ratio in the off-resonance regions by
up to $\pm 15%$ depending on the relative phase between the long and short
distance contributions. Using various phenomenological constraints including
the branching ratio of $b \rightarrow s \gamma$, we show that there are regions
in the parameter space where the branching ratio of $b \rightarrow s l^+ l^-$
is enhanced by about 50% compared to the SM. We also show that the branching
ratio of $b \rightarrow s \nu{\overline \nu}$ is reduced at most by 10% from
the SM prediction.


title:
Application of Pade Approximants to Determination of alpha_s(M_Z^2) from
  Hadronic Event Shape Observables in e+e- Annihilation

abstract:
  We have applied Pade approximants to perturbative QCD calculations of event
shape observables in e+e- --> hadrons. We used the exact O(alpha_s^2)
prediction and the [0/1] Pade approximant to estimate the O(alpha_s^3) term for
15 observables, and in each case determined alpha_s(M_Z^2) from comparison with
hadronic Z^0 decay data from the SLD experiment. We found the scatter among the
alpha_s(M_Z^2) values to be significantly reduced compared with the standard
O(alpha_s^2) determination, implying that the Pade method provides at least a
partial approximation of higher-order perturbative contributions to event shape
observables.


title:
Qualitative Aspects of Polarization Distributions In Excited Heavy
  Hadron Productions

abstract:
  Within the context of flux tube models, heavy quark fragmentation takes place
through the breaking of flux tubes with the production of a
(di)quark-anti(di)quark pair. It is found that the (di)quark produced are more
likely to be found in an $L_z=0$ state. This naturally leads to an supression
of the polarization distribution parameters $w_{3/2}$ and $\tilde w_1$ for
$(D_1, D_2^*)$ and $(\Lambda_{c1}, \Lambda_{c1}^*)$ production respectively.
The corresponding parameter $w_1$ for $(\Sigma_c, \Sigma_c^*)$ production,
however, is not suppressed, in agreement with the CLEO results but not the
DELPHI one. Implications on the measurements of $\Lambda_Q$ polarizations are
discussed.


title: Measurement of the Polarized Structure Function g_1^p at HERA

abstract:
  We present estimates of possible data on spin-dependent asymmetries in
inclusive scattering of high energy polarized electrons by high energy
polarized protons at HERA, including statistical errors, and discuss systematic
uncertainties. We show that these data would shed light on the small x
behaviour of the polarized structure function g_1, and would reduce
substantially the uncertainty on the determination of the polarized gluon
distribution.


title:
Detecting Neutrinos from AGNs and Topological Defects with Neutrino
  Telescopes

abstract:
  We evaluate neutrino-nucleon cross section for energies up to $10^{21} eV$ in
light of new information on the small-$x$ behavior of parton distributions. We
give predictions for large underground neutrino telescope event rates for
ultrahigh-energy neutrinos from Active Galactic Nuclei and from the decay of
topological defects formed in the early Universe.


title: Indirect Leptoquark Searches at Polarized Lepton Colliders

abstract:
  We examine the utility of employing polarized lepton (electron and muon)
beams to perform indirect searches for scalar leptoquarks. We find that
polarization can extend the reach in excluding leptoquark masses for both
$e^+e^-$ and $\mu^+\mu^-$ machines. Polarization can also provide a diagnostic
tool for determining leptoquark couplings.


title: Anatomy of the Higgs mass spectrum

abstract:
  We analyze the implications of a Higgs discovery on possible ``new-physics''
scenarios, for $m_H$ up to $\sim 700$ GeV. For this purpose we critically
review lower and upper limits on the Higgs mass in the SM and in the MSSM,
respectively. Furthermore, we discuss the general features of possible
``heavy'' ($m_H \gsim 2 m_Z$) Higgs scenarios by means of a simple
heavy-fermion condensate model.


title: Heavy Flavour Decays - Introduction and Overview

abstract:
  We review some selected topics in the decays of heavy flavours, beauty and
charm, which are of principal interest at HERA-B and HERA. The topics in $B$
physics include: an update on the quark mixing matrix and CP violating phases,
issues bearing on an improved resolution on the CP-violating phase $\Delta (sin
2 \beta)$, prospects of measuring radiative and semileptonic rare $B$ decays,
the $B_s^{0}$ - $\overline{B_s^{0}}$ mixing ratio $x_s$, improved measurements
of the $B_d^{0}$ - $\overline{B_d^{0}}$ mixing ratio $x_d$ and the $B$-hadron
lifetimes, in particular $\tau(\Lambda_b)$. In the charm sector, we have
focussed on rare decays and $D^0$- $\overline{D^0}$ mixing, whose measurements
will signal physics beyond the standard model.


title:
Longitudinal Polarization at future $e^+e^-$ Colliders and Virtual New
  Physics Effects

abstract:
  The theoretical merits of longitudinal polarization asymmetries of
electron-positron annihilation into two final fermions at future colliders are
examined, using a recently proposed theoretical description. A number of
interesting features, valid for searches of virtual effects of new physics, is
underlined, that is reminiscent of analogous properties valid on top of $Z$
resonance. As an application to a concrete example, we consider the case of a
model with triple anomalous gauge couplings and show that the additional
information provided by these asymmetries would lead to a drastic reduction of
the allowed domain of the relevant parameters.


title: NLO QCD calculations in DIS at HERA based on the dipole formalism

abstract:
  We briefly describe a new general algorithm for carrying out QCD calculations
to next-to-leading order in perturbation theory. The algorithm can be used for
computing arbitrary jet cross sections in arbitrary processes and can be
straightforwardly implemented in general-purpose Monte Carlo programs. We show
numerical results for the specific case of jet cross sections in deep inelastic
scattering at HERA energies.


title: Exclusive Decays of Beauty Hadrons

abstract:
  The principal difficulty in deducing weak interaction properties from
experimental measurements of $B$-decays lies in controlling the strong
interaction effects. In this talk I review the status of theoretical
calculations of the amplitudes for exclusive leptonic and semileptonic decays,
in the latter case with special emphasis on the extraction of the $V_{cb}$ and
$V_{ub}$ matrix elements.


title: CP Violation in $W\gamma$ and $Z\gamma$ Production

abstract:
  We study the capability of a $2 TeV$ $p\overline{p}$ collider with an
integrated luminosity of $10 fb^{-1}$ to study CP violation in the processes $p
\bar{p} \ra W^\pm \gamma$ and $p \bar{p} \ra Z \gamma$. We assume the existence
of new CP violating interactions beyond the standard model which we describe
with an effective Lagrangian. We find that the study of CP-odd observables
would allow this machine to place bounds on CP violating anomalous couplings
similar to the bounds that the same machine can place on $\cp$ conserving
anomalous couplings. For example it could place the bound
$|\tilde{\kappa}_\gamma|<0.1$ at the 95% confidence level.


title: Supersymmetric photonic signals at LEP

abstract:
  We explore and contrast the single-photon and diphoton signals expected at
LEP 2, that arise from neutralino-gravitino (e^+ e^- -> chi + gravitino ->
gamma + E_miss) and neutralino-neutralino (e^+ e^- -> chi + chi -> gamma +
gamma + E_miss) production in supersymmetric models with a light gravitino. LEP
1 limits imply that one may observe either one, but not both, of these signals
at LEP 2, depending on the values of the neutralino and gravitino masses:
single-photons for m_chi > Mz and m_gravitino < 3 x 10^-5 eV; diphotons for
m_chi < Mz and all allowed values of m_gravitino.


title:
From Current to Constituent Quarks: a Renormalization Group Improved
  Hamiltonian-based Description of Hadrons

abstract:
  A model which combines the perturbative behavior of QCD with low energy
phenomenology in a unified framework is developed. This is achieved by applying
a similarity transformation to the QCD Hamiltonian which removes interactions
between the ultraviolet cutoff and an arbitrary lower scale. Iteration then
yields a renormalization group improved effective Hamiltonian at the hadronic
energy scale. The procedure preserves the standard ultraviolet behavior of QCD.
Furthermore, the Hamiltonian evolves smoothly to a phenomenological low energy
behavior below the hadronic scale. This method has the benefit of allowing
radiative corrections to be directly incorporated into nonperturbative
many-body techniques. It is applied to Coulomb gauge QCD supplemented with a
low energy linear confinement interaction. A nontrivial vacuum is included in
the analysis via a Bogoliubov-Valatin transformation. Finally, the formalism is
applied to the vacuum gap equation, the quark condensate, and the dynamical
quark mass.


title: Testing a Model with extra Vector Fermions at the LEP2 Collider

abstract:
  Our aim is to test a model recently presented, motivated by the reported
$R_b$ and $R_c$ ``crisis", which contains extra vector fermions. We suggest an
alternative indirect test of the possible existence of new heavy quark flavours
at the LEP2 collider, which turns out to give the clearest signal. We calculate
$q\bar{q}$ cross sections within this framework, including one loop
corrections, and find measurable differences compared to the Standard Model
predictions.


title: Preheating in FRW Universes

abstract:
  The nonlinear time evolution of the quantum fields is studied in the O(N)
model for large N in a radiation dominated FRW universe, with a view towards
the phenomenon of explosive particle production due to either spinodal
instabilities or parametric amplification, i.e. preheating. Quantum
backreaction effects due to the produced particles are included consistently
within the large N approximation. We find that preheating persists when the
expansion is included, although the amount of particle production is reduced
compared to the values found in Minkowski space. We also see that the behavior
of the evolving zero mode is very different from that in Minkowski space,
though the late time behavior in all cases is determined by a sum rule that
implies the existence of Goldstone bosons in the final state.


title: Neutrino properties and SUSY without $R$-parity

abstract:
  In supersymmetric models without $R$-parity neutrinos naturally become
massive and mix with each other. We explore the predictions of a very
restricted model with only three free parameters and find that this model
naturally yields masses and mixing angles compatible with experimental results
from solar and atmospheric neutrino experiments. Furthermore, there is a tiny
region in parameter space where the solution to the solar neutrino puzzle is
compatible with either the LSND result or the existence of significant hot dark
matter neutrinos.


title: New Models of Gauge and Gravity Mediated Supersymmetry Breaking

abstract:
  We show that supersymmetry breaking in a class of theories with SU(N) x
SU(N-2) gauge symmetry can be studied in a calculable sigma model. We use the
sigma model to show that the supersymmetry breaking vacuum in these theories
leaves a large subgroup of flavor symmetries intact, and to calculate the
masses of the low-lying states. By embedding the Standard Model gauge groups in
the unbroken flavor symmetry group we construct a class of models in which
supersymmetry breaking is communicated by both gravitational and gauge
interactions. One distinguishing feature of these models is that the messenger
fields, responsible for the gauge mediated communication of supersymmetry
breaking, are an integral part of the supersymmetry breaking sector. We also
show how, by lowering the scale that suppresses the nonrenormalizable
operators, a class of purely gauge mediated models with a combined
supersymmetry breaking-cum-messenger sector can be built. We briefly discuss
the phenomenological features of the models we construct.


title: Final state rescattering as a contribution to $B \to \rho \gamma$

abstract:
  We provide a new estimate of the long-distance component to the radiative
transition $B \to \rho \gamma$. Our mechanism involves the soft-scattering of
on-shell hadronic products of nonleptonic $B$ decay, as in the chain $B \to
\rho\rho \to \rho\gamma$. We employ a phenomenological fit to scattering data
to estimate the effect. The specific intermediate states considered here modify
the $B \to \rho \gamma$ decay rate at roughly the $5 \to 8%$ level, although
the underlying effect has the potential to be larger. Contrary to other
mechanisms of long distance physics which have been discussed in the
literature, this yields a non-negligible modification of the $B^0 \to \rho^0
\gamma$ channel and hence will provide an uncertainty in the extraction of
$V_{td}$. This mechanism also affects the isospin relation between the rates
for $B^- \to \rho^-\gamma$ and $B^0 \to \rho^0 \gamma$ and may generate CP
asymmetries at experimentally observable levels.


title: Particle Dark Matter

abstract:
  Several ideas for new physics beyond the standard model may provide particle
candidates for the dark matter in the Galactic halo. The two leading candidates
are an axion and a weakly-interacting massive particle (WIMP), such as the
neutralino in supersymmetric extensions of the standard model. Several
possibilities for detection of such particles are discussed. An assessment of
the relative merits of various WIMP-detection techniques is given. I then
review the prospects for improving our knowledge of the amount, distribution,
and nature of the dark matter in the Universe from future maps of the cosmic
microwave background.


title: Binary String Dynamics

abstract:
  In this paper we investigate the dynamical properties of binary cosmic
strings. We find extrinsic curvature dependence of the string action and show
that kinks on binary strings are eroded while cusps can play a major role in
their evolution.


title: Disoriented Chiral Condensates in Hadron-Hadron Collisions

abstract:
  We review recent progress in the description and understanding of disoriented
chiral condensates. Certain important unsolved issues are underlined, and the
preliminary results of our program of investigation of these issues in the
framework of the classical linear sigma model are reported. We also briefly
review a formalism which could be useful at the full non-equilibrium quantum
field theory level of analysis.


title:
The Effect of Small-x Resummations on the Evolution of Polarized
  Structure Functions

abstract:
  The impact of the resummation of leading small-$x$ terms in the anomalous
dimensions is briefly summarized for the evolution of non--singlet and singlet
polarized structure functions.


title: QCD coherence and the soft limit of the energy spectrum

abstract:
  The analytical perturbative approach, if taken to the limit of its
applicability, allows one to predict an energy independent limit for the
one-particle invariant density in QCD jets E dn/d^3p at very small momenta p.
This is a direct consequence of the colour coherence in soft gluon branching.
The existing data on the charged and identified particle inclusive spectra
follow this prediction surprisingly well. Further tests of the perturbatively
based picture in the soft region are discussed.


title:
Combining Lattice QCD Results with Regge Phenomenology in a Description
  of Quark Distribution Functions

abstract:
  The most striking feature of quark distribution functions transformed to the
longitudinal distance representation is the recognizable separation of small
and large longitudinal distances. While the former are responsible for the
average properties of parton distributions, the latter can be shown to
determine specifically their small-$x$ behavior. In this paper we demonstrate
how the distribution at intermediate longitudinal distances can be approximated
by taking into account constraints which follow from the general properties of
parton densities, such as their support and behavior at $x \to 1$. We show that
the combined description of small, intermediate, and large longitudinal
distances allows a good approximation of both shape and magnitude of parton
distribution functions. As an application we have calculated low-virtuality C
even and odd (valence) u and d quark parton densities of the nucleon and the
C-even transversity distribution $h_1(x)$, combining recent QCD sum rules and
lattice QCD results with phenomenological information about their small-$x$
behavior.


title: Longitudinal and Transverse Nuclear Shadowing

abstract:
  Nuclear shadowing arises from multiple scattering of the hadronic
fluctuations of the virtual photon in a nucleus. We predict different
longitudinal and transverse shadowing and an A-dependence of R which can be up
to a 50% effect. The possibility of detecting nuclear effects on R at HERA is
discussed.


title: Power corrections in Drell-Yan production beyond the leading order

abstract:
  We study the power corrections to the cross-section of Drell-Yan production
within the Wilson line approach and apply the methods of QCD asymptotic
dynamics to identify the leading renormalon contribution.


title: Detecting New Physics from CP-violating phase measurements in B decays

abstract:
  The standard CKM model can be tested and New Physics detected using only
CP-violating phase measurements in B decays. This requires the measurement of a
phase factor which is small in the Standard Model, in addition to the usual
large phases $\beta$ and $\gamma$. We also point out that identifying
violations of the unitarity of the CKM matrix is rather difficult, and cannot
be done with phase measurements alone.


title: The static quark-antiquark potential in QCD to three loops

abstract:
  The static potential between an infinitely heavy quark and antiquark is
derived in the framework of perturbative QCD to three loops by performing a
full calculation of the two-loop diagrams and using the renormalization group.
The contribution of massless fermions is included.


title: Thermal Dileptons from pi - rho Interactions in a Hot Pion Gas

abstract:
  A systematic study of low mass dilepton production from $\pi-\rho$
interactions in a hot medium is presented. Applying finite temperature
perturbation theory the dilepton rate, respectively the virtual photon rate, is
computed up to order $g_\rho^2$. For dilepton masses below the $\rho$ the
two-body reactions $\pi\pi\to \rho \gamma^*$, $\pi\rho\to \pi \gamma^*$, and
the decay process $\rho \to \pi \pi \gamma^*$ give significant contributions.
Non-equilibrium contributions to the thermal rate are estimated, including the
modification of the particle distribution function with non-zero pion chemical
potential. The comparison of the dilepton rate with the recent data measured in
nucleus-nucleus collisions at SPS energy by the CERES Collaboration is also
performed. It is shown that the additional thermal dileptons from $\pi-\rho$
interactions can partially account for the access of the soft dilepton yield
seen experimentally.


title:
The Charm-Strange Contribution to Charged-Current DIS Structure
  Functions

abstract:
  We review the present theoretical knowledge of the charm--strange
contribution to charged--current DIS structure functions. In particular, the
uncertainties arising from the choice of the factorization scale, of the
massive QCD scheme, and of the parton fit are discussed.


title:
Theoretical uncertanties in the determination of $\alpha_s$ from
  hadronic event observables: the impact of nonperturbative effects

abstract:
  I review the theoretical status of hadronization corrections to hadronic
event observables and discuss their impact on the determination of $\alpha_s$.


title: Instanton-Induced Processes in Deep-Inelastic Scattering

abstract:
  We present a status report of our systematic theoretical and phenomenological
study of QCD-instanton induced processes in deep-inelastic scattering. We show
that this regime plays a distinguished role for studying manifestations of
QCD-instantons, since the typical hard momentum scale $Q$ provides a dynamical
infrared cutoff for the instanton size $\rho\lwig O(1/Q)$. For deep-inelastic
scattering at HERA, we present a preliminary theoretical estimate of the total
instanton-induced cross-section (subject to appropriate kinematical cuts). It
is surprisingly large, in the $ O(1-100)$ pb range, albeit still uncertain. We
report on our investigation of the discovery potential for instanton-induced
events at HERA by means of a Monte Carlo event generator. It is based on a
detailed study of the characteristic signatures of the final state, like a
large total transverse energy, $E_{T}= O(20)$ GeV, a large multiplicity, $n=
O(25)$, and a flavour-democratic production of hadrons. A combination of event
shape information with searches of $K^{0}$ mesons, muons, and multiplicity cuts
might help to discriminate further the QCD-instanton induced processes from the
standard perturbative QCD background.


title: Spin effects in lepton-nucleon scattering: a theoretical overview

abstract:
  I review recent theoretical results on polarized deep inelastic lepton
nucleon scattering. Some specific issues, like $Q^2$ evolution of structure
functions, the small $x$ behaviour, and the determination of polarized parton
densities, are discussed in some detail.


title: Low energy theorems and the SU(3)-flux-tube

abstract:
  The total energy and action, which is stored in the flux-tube between a
static quark-antiquark pair, can be compared with the potential of the pair
with the help of two low energy theorems. The flux-tube and the potential are
calculated in the framework of the model of the stochastic vacuum. Using the
low energy theorems we obtain consistency of the results and can predict the
scale where the model describes the non-perturbative gluon dynamics of QCD.


title: Testing CP, T and (V-A) Symmetry through Tau Leptons

abstract:
  Model independent tests for symmetry violations in tau decays are important
for determining whether the tau lepton is elementary or, instead, macroscopic.
Such tests are also significant steps towards resolving the outstanding "e - mu
- tau" puzzle. This talk reviews such tests in the context of a general
treatment of two-body tau decays which only assumes Lorentz invariance and the
tree-like structure of the tau-antitau production-decay sequence. Direct
measurement of polarized-partial-widths and of associated
``longitudinal-transverse W-exchange" interference intensities will provide
significant probes for distinguishing elementary/macroscopic theories of the
Higgs and of the tau, and tau-neutrino. The analogous goals and techniques
apply to top quark decays.


title:
Lifetime of $(\pi^+\pi^-)$ Atom: Analysis of the Role of Strong
  Interactions

abstract:
  The expression for the $(\pi^+\pi^-)$ atom lifetime is derived within the
Bethe-Salpeter approach. First-order perturbative corrections due to the
contribution of strong interactions are taken into account. It is demonstrated
that the atom lifetime can be expressed in terms of the solutions of the
Coulombic problem (the wave function of the $1S$ state at the origin
$\Psi_1(0)$, the binding energy of the $S$-state $E_1$), the difference of the
$S$-wave $\pi\pi$ scattering lengths and the energy shift $\Delta E_1$ of the
level due to the strong interactions: $ 1/(\tau_{1})\sim (a^0_0-a^2_0)^2
|\Psi_1(0)|^2 (1-(9\Delta E_1)/(8E_1))$


title: Z' Bosons and Supersymmetry

abstract:
  A broad class of supersymmetric extensions of the standard model predict a Z'
vector boson whose mass is naturally in the range 250 GeV < M_Z' < 2 TeV. To
avoid unacceptably large mixing with the Z, one requires either a discrete
tuning of the U(1)' charges or a leptophobic Z'. Both cases are likely to arise
as the low energy limits of heterotic string compactifications, but a survey of
existing realistic string models provides no acceptable examples. A broken
U(1)' leads to additional D-term contributions to squark, slepton, and Higgs
masses, which depend on the U(1)' charge assignments and the Z' mass. The
Tevatron and future colliders can discover or decisively rule out this class of
models.


title:
The radiative decay of the massive neutrino in the external
  electromagnetic fields

abstract:
  The radiative decay of the massive neutrino $\nu_i \rightarrow \nu_j \gamma$
is investigated in the framework of the Standard Model in external
electromagnetic fields of various configurations: constant crossed field,
constant uniform magnetic field, plane monochromatic wave's field. The effect
of significant enhancement of the neutrino decay probability by the external
field (electromagnetic catalysis) is discussed. An especially strong
enhancement occurs in the case of the ultrarelativistic neutrino decay, since
in this case the decay probability does not contain suppression caused by the
smallness of the decaying neutrino mass. The ultrarelativistic neutrino decay
catalysis is significant even in a relatively weak external field ($F/F_e <<
1$, where $F_e$ is the critical Schwinger value). The expression for the photon
splitting probability into the neutrino pair $\gamma \rightarrow \nu_i
\bar\nu_j$ in the wave field is given. The estimations of a number of
gamma-quanta produced in a volume filled with an electromagnetic field and the
neutrino lifetime in a strong magnetic field are presented.


title: Tensor Excitations in Nambu - Jona-Lasinio Model

abstract:
  It is shown that in the one-flavour NJL model the vector and axial-vector
quasiparticles described by the antisymmetric tensor field are generated. These
excitations have tensor interactions with quarks in contrast to usual vector
ones. Phenomenological applications are discussed.


title: Baryogenesis in a supersymmetric model without R-parity

abstract:
  We propose a simple scenario for baryogenesis in supersymmetric models where
baryon number is broken alongwith R-parity. The lightest supersymmetric
particle (neutralino) decays to three quarks and $CP-$ violation comes from
interference of tree and one loop box diagrams. The bounds on the $R-$parity
breaking couplings from the out-of-equilibrium condition are considerably
relaxed in this scenario.


title: Top Quark Mass

abstract:
  The influence of the top quark mass on mixing processes and precise
electroweak measurements is described. Experimental observation of the top
quark in proton-antiproton collisions is discussed, and some brief remarks are
made about electron-positron production. Some speculations are noted about the
possible significance of the large top quark mass.


title: The Light Quark Masses from Lattice Gauge Theory

abstract:
  We investigate the masses of the light quarks with lattice QCD. We show that
most of the large dependence on the lattice spacing, a, observed in previous
determinations using Wilson fermions is removed with the use of an O(a)
corrected action. In the quenched approximation, we obtain for the strange
quark MS bar mass m_s(2 GeV) = 95 (16) MeV, and for the average of the up and
down quark masses m_l(2 GeV) = 3.6 (6) MeV. Short distance arguments and
existing staggered fermion calculations make it likely that the answers
including the effects of quark loops lie 20 % to 40 % below this: m_s(2 GeV) in
the range 54-92 MeV, and m_l(2 GeV) in the range 2.1-3.5 MeV. We argue that
almost all lattice determinations of the light quark masses are consistent with
these values. These low values are outside the range usually given by
conventional phenomenology.


title:
QCD Improved $b\to s\gamma$ Constraints on the Minimal Supergravity
  Model

abstract:
  Recent advances in the QCD corrections to $b\to s\gamma$ decay in the MSSM
include i.) evaluation of the relevant operators, Wilson coefficients and
anomalous dimension matrix elements for the various MSSM effective theories
valid at scales beyond $Q =M_W$, ii.) calculations of most of the needed
anomalous dimension matrix elements to next-to-leading order for scales
$m_b\alt Q <M_W$, and iii.) calculations of ${\cal O}(\alpha_s)$ virtual and
bremsstrahlung corrections to the $b\to s\gamma$ decay operators at scale
$Q\sim m_b$. We assemble all these known results to gain an estimate of $B(b\to
s\gamma )$ for the parameter space of the minimal supergravity model (mSUGRA).
We find a much reduced scale dependence of our result compared to usual
leading-log evaluations. Comparison with the latest CLEO results yields
stringent constraints on parameter space. Much of mSUGRA parameter space is
ruled out for $\mu <0$, especially for large $tan\beta$. We compare these
results with other constraints from cosmology and non-standard vacua. Also, we
compare with expectations for discovering mSUGRA at LEP2, the Tevatron and the
CERN LHC.


title:
Baryon number segregation at the end of the cosmological quark-hadron
  transition

abstract:
  One of the most interesting questions regarding a possible first order
cosmological quark--hadron phase transition concerns the final fate of the
baryon number contained within the disconnected quark regions at the end of the
transition. We here present a detailed investigation of the hydrodynamical
evolution of an evaporating quark drop, using a multi-component fluid
description to follow the mechanisms of baryon number segregation. With this
approach, we are able to take account of the simultaneous effects of baryon
number flux suppression at the phase interface, entropy extraction by means of
particles having long mean-free-paths, and baryon number diffusion. A range of
computations has been performed to investigate the permitted parameter-space
and this has shown that significant baryon number concentrations, perhaps even
up to densities above that of nuclear matter, represent an inevitable outcome
within this scenario.


title:
The tricritical point of finite-temperature phase transitions in large
  N(Higgs) gauge theories

abstract:
  Gauge theories broken by a single Higgs field are known to have first-order
phase transitions in temperature if $\lambda/g^2 \ll 1$, where $g$ is the gauge
coupling and $\lambda$ the Higgs self-coupling. If the theory is extended from
one to $N$ Higgs doublets, with U($N$) flavor symmetry, the transition is known
to be second order for $\lambda/g^2 \gtrsim 1$ in the $N\to\infty$ limit. We
show that one can in principal compute the tricritical value of $\lambda/g^2$,
separating first from second-order transitions, to any order in $1/N$. In
particular, scalar fluctuations at the transition damp away the usual problems
with the infrared behavior of high-temperature non-Abelian gauge theories. We
explicitly compute the tricritical value of $\lambda/g^2$ for U(1) and SU(2)
gauge theory to next-to-leading order in $1/N$.


title:
QCD Sum Rules for The Double Ratio $(f_{B_s}/f_{B_d})
  /(f_{D_s}/f_{D_d})$ in HQET

abstract:
  The double ratio $(f_{B_s}/f_{B_d})/(f_{D_s}/f_{D_d})$ is calculated by QCD
sum rules in heavy quark effective theory (HQET), both numerically and
analytically. Our expression for the double ratio shows explicitly the
dependence on the light quark masses, the heavy quark symmetry breaking and the
vacuum condensates. The numerical result favors the double ratio to be a little
greater than 1.


title: Emission of Two Hard Photons in Large-Angle Bhabha Scattering

abstract:
  A closed expression for the differential cross section of the large-angle
Bhabha $e^+ e^-$ scattering which explicitly takes into account the leading and
next-to-leading contributions due to the emission of two hard photons is
presented. Both collinear and semi-collinear kinematical regions are
considered. The results are illustrated by numerical calculations.


title:
Studies of neutrino asymmetries generated by ordinary-sterile neutrino
  oscillations in the early universe and implications for big bang
  nucleosynthesis bounds

abstract:
  Ordinary-sterile neutrino oscillations can generate a significant lepton
number asymmetry in the early Universe. We study this phenomenon in detail. We
show that the dynamics of ordinary-sterile neutrino oscillations in the early
Universe can be approximately described by a single integro-differential
equation which we derive from both the density matrix and Hamiltonian
formalisms. This equation reduces to a relatively simple ordinary first order
differential equation if the system is sufficiently smooth (static limit). We
study the conditions for which the static limit is an acceptable approximation.
We also study the effect of the thermal distribution of neutrino momenta on the
generation of lepton number. We apply these results to show that it is possible
to evade (by many orders of magnitude) the Big Bang Nucleosynthesis (BBN)
bounds on the mixing parameters, $\delta m^2$ and $\sin^2 2\theta_0$,
describing ordinary-sterile neutrino oscillations. We show that the large angle
or maximal vacuum oscillation solution to the solar neutrino problem does not
significantly modify BBN for most of the parameter space of interest, provided
that the tau and/or mu neutrinos have masses greater than about 1 eV. We also
show that the large angle or maximal ordinary-sterile neutrino oscillation
solution to the atmospheric neutrino anomaly does not significantly modify BBN
for a range of parameters.


title:
The Physics of $K^0 -\bar K^0$ Mixing: $\widehat{B}_K$ and $\Delta
  M_{LS}$ in the Chiral Quark Model

abstract:
  We compute the $\widehat B_K$ parameter and the mass difference $\Delta
M_{LS}$ of the $K^0-\bar K^0$ system by means of the chiral quark model. The
chiral coefficients of the relevant $\Delta S=2$ and $\Delta S=1$ chiral
lagrangians are computed via quark-loop integration. We include the relevant
effects of one-loop corrections in chiral perturbation theory. The final result
is very sensitive to non-factorizable corrections of $O(\alpha_S N)$ coming
from gluon condensation. The size of the gluon condensate is determined by
fitting the experimental value of the amplitude $K^+ \to \pi^+\pi^0$. By
varying all the relevant parameters we obtain $\widehat{B}_K= 0.87 \pm 0.33\ .$
We evaluate within the model the long-distance contributions to $\Delta M_{LS}$
induced by the double insertion of the $\Delta S = 1$ chiral lagrangian and
study the interplay between short- and long-distance amplitudes. By varying all
parameters we obtain $\Delta M_{LS}^{th}/\Delta M_{LS}^{exp} = 0.76
^{+0.64}_{-0.34} .$ Finally, we investigate the phenomenological constraints on
the Kobayashi-Maskawa parameter Im $\lambda _t$ entering the determination of
$\epsilon'/\epsilon$.


title:
Measurement of the proton and deuteron structure functions, F2p and F2d,
  and of the ratio sigma(L)/sigma(T)

abstract:
  The muon-proton and muon-deuteron inclusive deep inelastic scattering cross
sections were measured in the kinematic range 0.002 < x < 0.60 and 0.5 < Q2 <
75 GeV2 at incident muon energies of 90, 120, 200 and 280 GeV. These results
are based on the full data set collected by the New Muon Collaboration,
including the data taken with a small angle trigger. The extracted values of
the structure functions F2p and F2d are in good agreement with those from other
experiments. The data cover a sufficient range of y to allow the determination
of the ratio of the longitudinally to transversely polarised virtual photon
absorption cross sections, R= sigma(L)/sigma(T), for 0.002 < x < 0.12 . The
values of R are compatible with a perturbative QCD prediction; they agree with
earlier measurements and extend to smaller x.


title: 1995-96 HERA Workshop; Beyond the Standard Model Group Summary

abstract:
  We summarize the work done in the ``Beyond the Standard Model'' group of the
1995-96 HERA Workshop. Of the various proposed HERA upgrades, the luminosity
improvement is the most important for this physics. With an integrated
luminosity of 1 $fb^{-1}$, collected by 2005, HERA will remain a competitive
and potentially fruitful facility for new physics searches. The full
proceedings of the group with the individual reports can be found at:
http://ucosun.desy.de/~heraws96/proceedings/beyondSM/ The topics covered
include:
  1. Higgs Physics
  2. Contact Interactions and Compositeness
  3. Lepton Flavor Violation
  4. Heavy Neutral Leptons
  5. Supersymmetry
  5.1 MSSM
  5.2 R-Parity Violation
  5.3 Light Gluinos
  6. Leptoquarks


title:
Constraints on Supersymmetric Models from the Muon Anomalous Magnetic
  Moment

abstract:
  We study the impact of present and future $(g-2)_\mu$ measurements on
supersymmetric models. The corrections to $(g-2)_\mu$ become particularly
relevant in the presence of light sleptons, charginos and neutralinos,
especially in the large $\tan\beta$ regime. For moderate or large values of
$\tan\beta$, it is possible to rule out scenarios in which charginos and
sneutrinos are both light, but nevertheless escape detection at the LEP2
collider. Furthermore, models in which supersymmetry breaking is transferred to
the observable sector through gauge interactions can be efficiently constrained
by the $(g-2)_{\mu}$ measurement.


title: Topics in Jet Physics

abstract:
  We review two subjects in the theoretical study of jet production at the
Tevatron collider: the uncertainties in the determination of the partonic
densities inside the proton and the uncertainties in the calculation of
higher-order corrections to the QCD matrix elements.


title: No-scale supergravity confronts LEP diphoton events

abstract:
  We examine the possibility that some anomalous acoplanar diphoton events
observed at LEP may be consistent with the predictions of our previously
proposed one-parameter no-scale supergravity model with a light gravitino, via
the process e^+e^- -> chi chi -> gamma gamma+E_miss. We find that one such
event may indeed be consistent with the model predictions for m_chi \approx
(60-70) GeV. This region of parameter space is also consistent with the
selectron and chargino interpretations of the CDF ee gamma gamma + E_T,miss
event.


title: Comments on glueballinos (R0 particles) and R0 searches

abstract:
  We propose a search strategy for the light R0 (glueballino) particle
suggested by G.Farrar in connection with the light gluino scenario. The basic
idea is to moderate and stop the R0 particles and then observe their decay to
almost monochromatic pions - at an appropriate time delay relative to a primary
collision event, where a gluino jet, likely to fragment into the R0, was
produced. This technique is optimized at colliders and depends on qualitative
features of the R0 hadronic interactions which we discuss in detail.


title: Searching for Doubly-Charged Higgs Bosons at Future Colliders

abstract:
  Doubly-charged Higgs bosons ($\Delta^{--}/\Delta^{++}$) appear in several
extensions to the Standard Model and can be relatively light. We review the
theoretical motivation for these states and present a study of the discovery
reach in future runs of the Fermilab Tevatron for pair-produced doubly-charged
Higgs bosons decaying to like-sign lepton pairs. We also comment on the
discovery potential at other future colliders.


title: Polarized structure functions: a status report

abstract:
  We review the present status of polarized structure functions measured in
deep-inelastic scattering. We discuss the x and Q^2 dependence of the structure
function g_1, and how it can be used to test perturbative QCD at
next-to-leading order and beyond. We summarize the current knowledge of
polarized parton distributions, in particular the determination of the first
moment of the quark and gluon distributions and the axial charge of the
nucleon. We critically examine what future experiments could teach us on the
polarized structure of the nucleon.


title: Production of the B_c Meson

abstract:
  The production of the B_c and B_c^* mesons was studied in the framework of
the factorization formalism and perturbative QCD. Predicted results implied
that an observable number of B_c and B_c^* events can be produced at LEP I and
at Tevatron. The fragmentation approximation describes the production of the
B_c and B_c^* mesons very well in high energy e^+e^- collisions. In hadronic
collisions, it is valid when and only when the transverse momentum P_T of the
produced B_c and B_c^* is much larger than the mass of the B_c meson.


title: Signals of Dynamical Supersymmetry Breaking in a Hidden Sector

abstract:
  If supersymmetry is dynamically broken in a hidden sector, the gauginos
typically have unacceptably small masses. This situation can be corrected if a
non-Abelian gauge interaction becomes strong at a scale of order 1 TeV and
induces dynamical gaugino masses. We discuss the typical signals of this
scenario at present and future colliders.


title:
Spin and Flavor Content of Constituent Quarks and One-Spin Asymmetries
  in Inclusive Processes

abstract:
  We discuss a nonperturbative mechanism for one-spin asymmetries in inclusive
hadron production. The main role in generation of this asymmetry belongs to the
orbital angular momentum of quark-antiquark cloud in internal structure of
constituent quarks.


title:
Constraints on the tau neutrino mass and mixing from precise
  measurements of tau decay rates

abstract:
  We have derived constraints on the tau neutrino mass and fourth generation
mixing from an analysis of the partial widths of tau lepton decays, in
particular: tau -> e nu nu_tau, tau -> mu nu nu_tau, tau -> pi nu_tau, tau -> K
nu_tau. We present predictions for the tau decay widths, allowing for a
non-zero tau neutrino mass, m(nu_tau), and for mixing with a neutrino of mass
m(nu_L) > M_Z/2, which is parametrised using a Cabibbo-like mixing angle,
theta_L. By comparison of these theoretical predictions with the experimental
measurements, we obtain the following bounds at the 90% confidence level:
m(nu_tau) < 42 MeV and sin^2(theta_L) < 0.014.


title: Rare Kaon Decays

abstract:
  Rare K decays are an important testing ground of the electroweak flavour
theory. They can provide new signals of CP-violation phenomena and, perhaps, a
window into physics beyond the Standard Model. The interplay of long-distance
QCD effects in strangeness-changing transitions can be analyzed with Chiral
Perturbation Theory techniques. Some theoretical predictions obtained within
this framework for radiative kaon decays are reviewed, together with the
present experimental status.


title:
Vector meson exchange contributions to K --> pi gamma gamma and K(L) ->
  gamma lepton+ lepton-

abstract:
  We have studied in the framework of Chiral Perturbation Theory (ChPT) the
O(p^6) Vector Meson contributions to K -> pi gamma gamma and K(L) -> gamma
gamma^*. We construct the most general ChPT lagrangian for the weak
Vector-Pseudoscalar-Photon (VPgamma) vertex for K -> pi gamma gamma and K(L) ->
gamma gamma^* and consequently we get the full structure of the O(p^6) local
contributions generated by Vector Meson exchange. Then we compute new
factorizable contributions to the weak VPgamma vertex generated by the
odd-intrinsic parity violating lagrangian with no additional couplings. We find
in fact a very nice agreement with the phenomenology of K -> pi gamma gamma and
K(L) -> gamma gamma^*, more predictive power and a deeper understanding of the
O(p^6) local operators. A novel interpretation of the K(L) -> gamma gamma^*
data is given. Also a comparison with the existing models is presented.


title: Diffractive structure functions in DIS

abstract:
  A review of theoretical models of diffractive structure functions in deep
inelastic scattering (DIS) is presented with a view to highlighting distinctive
features, that may be distinguished experimentally. In particular, predictions
for the behaviour of the diffractive structure functions $F_2^D, F_L^D,
F_2^{D(\mbox{\small{charm}})}$ are presented. The measurement of these
functions at both small and high values of the variable $\beta$ and their
evolution with $Q^2$ is expected to reveal crucial information concerning the
underlying dynamics.


title:
A Program for Baryon Generation and Its Applications to Baryon
  Fragmentation in DIS

abstract:
  In an earlier paper, we discuss the ``popcorn'' model for baryon production
in quark and gluon jets, and present an improved model (which we call Modified
Popcorn Scenarium, MOPS). In this paper we give a manual to the MC program
based on MOPS, and also discuss the application of the model to baryon
fragmentation, i.e. fragmentation of strings originally contaning a diquark.
Model predictions for baryon production in DIS are compared with data.


title: Finite temperature effective theories

abstract:
  Lecture Notes, Summer School on Effective Theories and Fundamental
Interactions, Erice, July 1996. I describe the construction of effective field
theories for equilibrium high-temperature plasma of elementary particles.


title: Supersymmetric inflation and large-scale structure

abstract:
  In effective supergravity theories following from the superstring, a modulus
field can quite naturally set the neccessary initial conditions for successful
cosmological inflation to be driven by a hidden sector scalar field. The
leading term in the scalar potential is {\em cubic} hence the spectrum of
scalar density perturbations neccessarily deviates from scale-invariance, while
the generation of gravitational waves is negligible. The growth of large-scale
structure is then consistent with observational data assuming a critical
density cold dark matter universe, with no need for a component of hot dark
matter. The model can be tested thorough measurements of cosmic microwave
background anisotropy on small angular scales.


title: On the extreme behaviour of $g_1(x,Q^2)$ at $x\to 0$

abstract:
  On the basis of the U-matrix form of s-channel unitarization, we consider
constraints unitarity provides for the spin structure function $g_1(x,Q^2)$ at
$x\to 0$. Corresponding constraint for the spin structure function $h_1(x,
Q^2)$ is given along.


title: Gluonic Mesons in J/Psi Radiative Decay

abstract:
  The eta(1760) may be significantly produced in J/Psi radiative decay. We
deduce from experimental data that its branching ratio to two gluons is
bounded, 0.4 +- 0.3 < BR(eta(1760) -> gg) < 0.9 +- 0.3, consistent with gluonic
admixture. Moreover, the expectation that there should be an isoscalar analogue
of the gluonic (hybrid) meson candidate pi(1800) is argued to reinforce hybrid
admixture in eta(1760). Two-gluon coupling of hybrids is estimated in a
spectator model to be considerably larger than that of quarkonium. In addition,
the two-photon coupling of eta(1760) is estimated to be 1.4 +- 0.7 keV.


title: Electroweak Physics at HERA: Introduction and Summary

abstract:
  A high luminosity upgrade of HERA will allow the measurement of standard
model parameters and the neutral current couplings of quarks. These results
will have to be consistent with other precision measurements or indicate traces
of new physics. The analysis of $W$ production will complement future results
of LEP 2 and the Tevatron. We summarize the main results and conclusions
obtained by the working group on Electroweak Physics concerning the potential
of future experimentation at HERA.


title: B-factory Physics from Effective Supersymmetry

abstract:
  We discuss how to extract non-Standard Model effects from B-factory
phenomenology. We then analyze the prospects for uncovering evidence for
Effective Supersymmetry, a class of supersymmetric models which naturally
suppress flavor changing neutral currents and electric dipole moments without
squark universality or small CP violating phases, in experiments at BaBar,
BELLE, HERA-B, CDF/D0 and LHC-B.


title:
Neutrino Radiative Decay in an External Electromagnetic Field via Vector
  Leptoquark

abstract:
  The massive neutrino radiative decay $\nu_i \rightarrow \nu_j \gamma$ ($i \ne
j$) is investigated within the Minimal Quark-Lepton Symmetry of the Pati-Salam
type based on the $SU(4)_V \times SU(2)_L \times G_R$ group in an external
constant crossed field ($\vec {\cal E} \perp \vec H$, ${\cal E}=H$). The matrix
element $\Delta M^{(X)}$ and the decay probability $W^{(X)}$ due to the
leptoquark $X$ contribution are analysed. The effect of significant enhancement
of the neutrino decay by the crossed field takes place. It is shown that the
leptoquark contribution to the decay probability can dominate over the
$W$-boson one in the case of strong suppression of the lepton mixing in the
framework of the SM.


title: QCD Sum Rules and the Validity of Effective Models

abstract:
  The consistency of effective models with QCD is investigated through the use
of the QCD sum rule. Taking the potential model for the heavy quark system, we
apply the method to two phenomenologically successful parameter sets, and
obtain the dependences of the model parameters on the QCD scale $\Lambda$.
Comparison with the expected scaling laws allows us to reject one of the two
sets. The method is applicable to any model which reproduces the low lying
spectra of hadronic systems.


title: Rare B -> Nu Barnu Gamma Decay in Light Cone QCD Sum Rule

abstract:
  Using the light cone QCD Sum Rules Method, we study the rare B -> nu barnu
gamma decay and and find that the branching ratios are, B(B_s -> nu barnu
gamma) = 7.5 10^{-8}, B(B_d -> nu -> nu gamma) = 4.2 10^{-9}. A comparision of
our results, on branching ratio, with constituent quark and pole dominance
model predictions are presented.


title: Excited Heavy Mesons Decay Formfactors in Light Cone QCD

abstract:
  The formfactors of B_1 -> pi and D_1 -> pi transitions, where B_1(D_1) is the
1^+ P-wave -> Q gamma_{\nu}\gamma_5q meson state, are calculated in the
framework of the light cone QCD. Furthermore these formfactors are compared
with the pole dominance model prediction using the values of the strong
coupling constants g_{B_1 B^* pi} and g_{D_1 D^* pi}, and a good agreement
between these two different descriptions is observed.


title: Neutrino Mass Models with an Abelian Family Symmetry

abstract:
  Abelian family symmetries provide a predictive framework for neutrino mass
models. In seesaw models based on an abelian family symmetry, the structures of
the Dirac and the Majorana matrices are derived from the symmetry, and the
neutrino masses and mixing angles are determined by the lepton charges under
the family symmetry. Such models can lead to mass degeneracies and large mixing
angles as well as mass hierarchies, the squared mass difference between
quasi-degenerate neutrinos being determined by the symmetry. We present two
models illustrating this approach.


title:
Pseudoscalar neutral Higgs Boson production in polarized (gamma e)
  collisions

abstract:
  We investigate the pseudoscalar neutral Higgs-boson A^0 production in the
polarized (gamma e) collisions with two different center of mass energies
sqrt{s} = 500 GeV and sqrt{s} = 1 TeV. The cross-section of the process (gamma
e -> e A^0) and the polarization asymmetry due the spin of the initial beams
are calculated.


title: Long Range Physics in a Hot Non-Abelian Plasma

abstract:
  We derive a set of equations describing the real time dynamics of modes with
spatial momentum of order g^2 T in a high temperature gauge theory, where g is
the coupling constant and T is the temperature. This dynamics is stochastic in
nature. Important implications for baryon number violation at high temperature
and for the physics at the electroweak phase transition, are discussed.


title: Probing the QCD pomeron in e+ e- collisions

abstract:
  The total cross section for scattering virtual photons at high energy is
sensitive to pomeron physics. If the photons are sufficiently virtual, QCD
perturbation theory applies, so that the reaction probes the short distance
pomeron. We study this reaction for present and future e+/- e- colliders.


title:
A (Slightly Less Brutal) Method for Numerically Evaluating Structure
  Functions

abstract:
  A fast numerical algorithm for the evolution of parton distributions in x
space is described. The method is close in spirit to `brute' force techniques.
The necessary integrals are performed by summing the approximate contributions
from small steps of the integration region. Because it is a numerical
evaluation it shares the advantage with brute force numerical integration that
there are no restrictions placed on the functional form of the distributions to
be evolved. However, an improvement in the approximation technique results in a
significant reduction in the number of integration steps and a savings in time
on the order of three hundred fifty. The method has been implemented for the
structure functions F_2 and g_1 at next-to-leading order.


title: Rayleigh-Ritz Variational Approximation and Symmetry Nonrestoration

abstract:
  The investigation of symmetry nonrestoration scenarios has led to a
controversy, with certain nonperturbative approximation schemes giving
indications in sharp disagreement with those found within conventional
perturbation theory. A Rayleigh-Ritz variational approach to the problem, which
might be useful in bridging the gap between perturbative and nonperturbative
viewpoints, is here proposed. As a first application, this approach is used in
the investigation of a $Z_2 \times Z_2$-invariant thermal field theory with two
scalar fields, placing particular emphasis on the region of parameter space
that has been claimed to support symmetry nonrestoration.


title: On Dynamics of Fractality in Central C-Cu Collisions at 4.5A Gev/c

abstract:
  Fractal structure of charged particle distributions in the pseudorapidity and
transverse momentum in central C-Cu collisions at 4.5A GeV/c is studied by
means of intermittency approach and multifractal analysis. The modifications to
take into account statistical bias are applied. Intermittency study in the
pseudorapidity phase space indicates a non-thermal phase transition and
different regimes of multiparticle production. Multifractality is observed
within the both methods applied. The interrelation of the methods using the
effective average multiplicity approach is studied. The findings support the
idea of statistical significance of influence of finite multiplicities. In the
transverse momentum spectrum no dynamical fluctuations are found.


title: Can Strong QCD in the Early Universe Raise the Axion Decay Constant?

abstract:
  We report that the hypothesis that the upper bound on the axion decay
constant can be moved up beyond $10^{12}$ GeV in models with a stronger QCD in
the early universe is not realized. This proof is possible by studying the
superpotential in the dual model and obtaining the form of the axion potential
respecting the original global symmetries.


title: Colour-octet contributions to exclusive charmonium decays

abstract:
  We investigate the theoretical uncertainties of $P$-wave charmonium decays
into two pions, $\chi_{\c J}\rightarrow \pi^+\pi^-$, $\pi^0\pi^0$. Constraining
the pion distribution-amplitude from the recent precise data on
$F_{\pi\gamma}(Q^2)$, we find an order-of-magnitude discrepancy between data
and prediction. The disagreement persists even after inclusion of transverse
degrees of freedom and Sudakov suppressions. We propose the colour-octet
mechanism as the solution to the puzzle. The colour-octet decay contribution
arising from the higher Fock component $|\c \cbar \g >$ of the $\chi_{\c J}$
wave function is actually not power suppressed with respect to the usual
colour-singlet decay arising from the dominant $|\c \cbar >$ Fock state. An
explicit calculation yields an agreement with the data for a very reasonable
value for the single extra non-perturbative parameter.


title: Heavy-Quark Effective Theory

abstract:
  We give an introduction to the heavy-quark effective theory and the $1/m_Q$
expansion, which provide the modern framework for a systematic,
model-independent description of the properties and decays of hadrons
containing a heavy quark. We discuss the applications of these concepts to
spectroscopy and to the weak decays of $B$ mesons.


title: Large-p_T Photoproduction of D^*+- Mesons in ep Collisions

abstract:
  The cross section for the inclusive photoproduction of large-p_T D^*+- mesons
is calculated at next-to-leading order, adopting different approaches to
describe the fragmentation of charm quarks into D^*+- mesons. We treat the
charm quark according to the massless factorization scheme, where it is assumed
to be one of the active flavours inside the proton and the photon. We present
inclusive single-particle distributions in transverse momentum and rapidity,
including the contributions due to both direct and resolved photons. We compare
and assess the various implementations of fragmentation. We argue that, in the
high-p_T regime, a particularly realistic description can be obtained by
convoluting the Altarelli-Parisi-evolved fragmentation functions of Peterson et
al. with the hard-scattering cross sections of massless partons where the
factorization of the collinear singularities associated with final-state charm
quarks is converted to the massive-charm scheme. The predictions thus obtained
agree well with recent experimental data by the H1 and ZEUS Collaborations at
DESY HERA.


title: Double Asymptotic Scaling '96

abstract:
  We review recent HERA data on the structure function F_2 at small x and large
Q^2. We show that the salient features of the data are revealed by comparing
them to the double asymptotic scaling behaviour which F_2 is predicted to
satisfy in perturbative QCD.


title: $\pi \to l\nu \gamma$ Form Factors at Two-loop

abstract:
  Within Chiral Perturbation Theory (CHPT) we compute the form factors A, V and
$\gamma = A/V$ in the $\pi \to \nu l \gamma$ decay to $O(p^6)$. A and $\gamma$
obtain corrections of order 25%.


title: A Perturbative Gluon Condensate?

abstract:
  I propose that the properties of QCD perturbation theory should be
investigated when the boundary state (`perturbative vacuum') at $t= \pm\infty$
includes gluons. Any boundary state that has an overlap with the true QCD
ground state generates a perturbative series that (when summed to all orders)
is formally exact. Through an analogy with the boundary condition corresponding
to a fermion condensate, I propose an explicit form for a `perturbative gluon
condensate' that suppresses low momentum gluon production, thus generating an
effective mass gap. Standard perturbative calculations are modified only
through a change in the $i\epsilon$ prescription of low momentum $(|\pv| \lsim
\Lambda_{QCD})$ gluon propagators. Gauge invariance is expected to be preserved
since this modification is equivalent to adding on-shell external particles.
Renormalizability is unaffected since only low-momentum propagators are
modified. Due to the asymptotic low momentum gluons boost invariance is not
explicit. Lorentz invariance should be restored in the sum to all orders in
analogy to standard bound state calculations.


title:
Threshold effects and radiative electroweak symmetry breaking in $SU(5)$
  extensions of the MSSM

abstract:
  We make a complete analysis of radiative symmetry breaking in the MSSM and
its $SU(5)$ extensions including low- and high-energy threshold effects in the
framework of the two-loop renormalization group. In particular, we consider
minimal $SU(5)$, the ``missing-doublet'' $SU(5)$, a Peccei-Quinn invariant
version of $SU(5)$ as well as a version with light adjoint remnants. We derive
permitted ranges for the parameters of these models in relation to predicted
$\alpha_{s}$ and $M_G$ values within the present experimental accuracy. The
parameter regions allowed under the constraints of radiative symmetry breaking,
perturbativity and proton stability, include the experimentally designated
domain for $\alpha_s$. In the case of the minimal $SU(5)$, the values of
$\alpha_s$ obtained are somewhat large in comparison with the experimental
average. The ``missing-doublet'' $SU(5)$, generally, predicts smaller values of
$\alpha_s$. In both versions of the ``missing-doublet'', the high energy
threshold effects on $\alpha_s$ operate in the opposite direction than in the
case of the minimal model, leading to small values. In the case of the
Peccei-Quinn version however the presence of an extra intermediate scale allows
to achieve an excellent agreement with the experimental $\alpha_s$ values.
Finally, the last considered version, with light remnants, exhibits unification
of couplings at string scale at the expense however of rather large $\alpha_s$
values.


title: Matching conditions and Higgs mass upper bounds revisited

abstract:
  Matching conditions relate couplings to particle masses. We discuss the
importance of one-loop matching conditions in Higgs and top-quark sector as
well as the choice of the matching scale. We argue for matching scales
$\mu_{0,t} \simeq m_t$ and $\mu_{0,H} \simeq max[ m_t, M_H ]$. Using these
results, the two-loop Higgs mass upper bounds are reanalyzed. Previous results
for $\Lambda\approx$ few TeV are found to be too stringent. For
$\Lambda=10^{19}$ GeV we find $M_H < 180 \pm 4\pm 5$ GeV, the first error
indicating the theoretical uncertainty, the second error reflecting the
experimental uncertainty due to $m_t=175\pm6$ GeV.


title: Perturbation Theory and Its Limitations in the Higgs Sector of the SM

abstract:
  This lecture reviews various Higgs-sector amplitudes which have been
calculated to two loops in the Higgs quartic coupling. After explaining the
framework of these calculatins, the perturbative behaviour of the amplitudes is
discussed, and perturbative upper bounds on the Higgs boson mass are given.


title: Interaction of small size wave packet with hadron target

abstract:
  We calculate in QCD the cross section for the scattering of an energetic
small-size wave packet off a hadron target. We use our results to study the
small-$\sigma$ behaviour of $P_{\pi}(\sigma)$, the distribution over cross
section for the pion, in the leading $\alpha_{s}$-order.


title:
Renormalization of the three flavor Lagrangian in heavy baryon chiral
  perturbation theory

abstract:
  The complete renormalization of the generating functional for Green functions
of quark currents between one--baryon states in three flavor heavy baryon
chiral perturbation theory is performed to order q^3. As an example, we study
the kaon loop induced divergences in neutral pion photoproduction off protons.


title: Small-x physics in perturbative QCD

abstract:
  We review the parton model and the Regge approach to the QCD description of
the deep-inelastic $ep$ scattering at the small Bjorken variable $x$ and
demonstrate their relation with the DGLAP and BFKL evolution equations. It is
shown, that in the leading logarithmic approximation the gluon is reggeized and
the pomeron is a compound state of two reggeized gluons. The conformal
invariance of the BFKL pomeron in the impact parameter space is used to
investigate the scattering amplitudes at high energies and fixed momentum
transfers. The remarkable properties of the Schr\"odinger equation for compound
states of an arbitrary number of reggeized gluons in the multi-colour QCD are
reviewed. The gauge-invariant effective action describing the gluon-Reggeon
interactions is constructed. The known next-to-leading corrections to the QCD
pomeron are discussed.


title:
Exclusive versus Inclusive Semileptonic $\bar B$ Decays in the Quark
  Model

abstract:
  Some emerging difficulties in the theoretical description of exclusive
semileptonic $\bar B$ decays are discussed in the context of the quark model.
While there are no unambiguous problems at this time, I discuss physics beyond
the valence quark model which should eventually be probed by precision
measurements of $\bar B$ semileptonic decays.


title:
Chromo-electroweak interference and parity-violating asymmetries in the
  production of an electroweak boson + two jets in hadron collisions

abstract:
  In the Standard Model the process $q\bar{q}\rightarrow q\bar{q}V$ (where
$V=W^\pm,Z^0$ or $\gamma$) can occur via gluon exchange and also via $W^\pm$ or
$Z^0$ exchange. The corresponding chromodynamic and electroweak amplitudes can
interfere with one another. These interference cross sections are largest when
the exchanged $W^\pm$ or $Z^0$ is on-shell when they are also odd under parity.
Interference cross sections computed using helicity-amplitude techniques are
presented for all interesting subprocesses as well as for the processes
$q\bar{q}\rightarrow q\bar{q} l\bar{l}$ in which the lepton pair $l\bar{l}$
comes from the decay of $V$ on-shell. Parity-violating asymmetries are defined
and presented at the parton level and for the hadronic processes $pp$ or
$p\bar{p}\rightarrow V$ + 2 jets or $l\bar{l}$ + 2 jets. These asymmetries are
independent of the polarizations of all particles involved, and do not require
that the flavors of the jet partons be measured. They are generally of order
0.01 pb at energies $\sqrt{s} \gtrsim 1$ TeV.


title: A Manifestly Gauge-Invariant Approach to Charged Particles

abstract:
  In this article we provide a manifestly gauge-invariant approach to charged
particles. It involves (1) Green functions of gauge-invariant operators and (2)
Feynman rules which do not depend on any kind of gauge-fixing condition. First,
we provide a thorough analysis of QED. We propose a specific set of
gauge-invariant Green functions and describe a manifestly gauge-invariant
technique to evaluate them. Furthermore we show how Green's functions and
Feynman rules of the manifestly gauge-invariant approach and of the Faddeev-
Popov ansatz are related to each other. Finally, we extend this manifestly
gauge-invariant approach to the Standard Model of electroweak interactions.
  Motivation for such an approach is abundant. A gauge-dependent framework does
obstruct not only theoretical insight but also phenomenological analyses of
precision experiments at LEP. Unresolved issues include the analysis of finite
width effects of unstable particles and of oblique corrections parametrised by,
e.g., S, T, and U. Quite another example of considerable complications caused
by a gauge-dependent framework is the matching of a full and an effective
theory, relevant for effective field theory analyses of the symmetry-breaking
sector of the Standard Model.