title: Radiative Dileptonic Decays of B Mesons

abstract:
  We investigate the radiative dileptonic decays $B_s(B_d)\to\gamma l^+l^-$
within the standard model. Using the constituent quark model, the branching
ratios turn out to be around $5\times 10^{-9}$ for $B_s\to \gamma \mu^+\mu^- $
and around $6\times 10^{-10}$ for $B_d \to \gamma \mu^+\mu^- $, with slightly
larger values for $B_s(B_d) \to \gamma e^+e^- $. The differential rate as a
function of the dilepton invariant mass is given. The possibility of using
these processes to determine the decay constants of $B_s$ or $B_d$ is
discussed.


title: Supernova Bounds on Supersymmetric $R$-parity Violating Interactions

abstract:
  We re-examine resonant massless-neutrino conversions in a dense medium
induced by flavour changing neutral current (FCNC) interactions. We show how
the observed $\bar\nu_e$ energy spectra from SN1987a and the supernova
$r$-process nucleosynthesis provide constraints on supersymmetric models with
$R$ parity violation, which are much more stringent than those obtained from
the laboratory. We also suggest that resonant massless-neutrino conversions may
play a positive role in supernova shock reheating. Finally, we examine the
constraints on explicit $R$-parity-violating FCNCs in the presence of non-zero
neutrino masses in the eV range, as indicated by present hot dark matter
observations.


title:
How Georgi-Jarlskog and SUSY-SO(10) imply a measurable rate for mu->e
  gamma

abstract:
  Slepton mass matrices have been analyzed in an SO(10) SUSY-GUT, with
soft-breaking terms generated at Planck scale. Higher dimensional operators
consistent with 4-d string constructions are used in order to generate a
Georgi-Jarlskog (G-J) Yukawa texture at \mgut. Radiative corrections between
\mpl\ and \mgut\ generate a substantial non-universality in the
$\tilde\mu-\tilde e$ sector. This non-universality originates in the flavor
dependence of the Higgs assignments required for the G-J texture, and is
unrelated to the large top Yukawa. The resulting branching ratio for mu->e
could make this process observable for large sectors of the MSSM parameter
space, with a factor of 10 improvement in statistics.


title: Magnitude of R-parity violation in String Inspired GUTs

abstract:
  The nature of R-parity violating interactions in two classes of string
inspired supersymmetric grand unified theories (SISUSY GUT), based on the gauge
groups $SO(10)$ (and its subgroup $SU(2)_L\times SU(2)_R\times SU(4)_c\equiv
G_{224}$) as well as $[SU(3)]^3$, are discussed and their strengths are related
to the ratio of symmetry breaking scales present in the model. We first argue
that for the R-parity violating couplings $\lambda_{R\!\!\!/}$ to be suppressed
to the desired level, the $B-L$ local symmetry must break at an intermediate
scale $M_{B-L}$ since $\lambda_{R\!\!\!/} =M_{B-L}/M_{GUT}$. We then construct
scenarios where such intermediate scales arise being consistent with gauge
coupling unification in a two-loop renormalization group study. In the
resulting $SO(10)$ models, higher-dimensional-operator-induced R-parity
violating couplings are potentially large (except in one case), and are
therefore inconsistent with limits on the proton life time unless the couplings
associated with the higher dimensional terms are fine tuned to very small
values. However, the $[SU(3)]^3$ and $G_{224}$ models can be consistent if a
certain class of quark-lepton coupling in the superpotential is forbidden by a
discrete summetry (unrelated to R-parity). An interesting prediction of these
models is neutron-anti-neutron oscillation with observable strength.


title:
Diffractive Factorization - a Simple Field Theory Model for
  $F_2^{diff}(\beta x_{\pom}, Q^2; x_{\pom},t)$

abstract:
  Operator definitions of diffractive parton distribution functions are given.
A distinction is made between the special case of ``Regge factorization'' to
the general case of ``diffractive factorization'' with explicit expressions for
$F_2^{diff}(\beta x_{\pom}, Q^2;x_{\pom},t)$ in both cases. A calculation from
a simple field theory model is presented in the style of ``constituent counting
rules'' for the behavior of the diffractive parton distribution functions when
$\beta \rightarrow 1$, which corresponds to when the detected parton carries
almost all of the longitudinal momentum transferred from the scattered hadron.
A comment is made about the consistency of the model with the observed
flattening of $n(\beta)$ as $\beta \rightarrow 1$, which recently was reported
by the H1-collaboration from their preliminary 1994 data.


title: Excluding Light Gluinos from Z decays

abstract:
  We reanalyze the constraints on light gluinos (m_{\tilde{g}}\leq 5 GeV/c^2)
from the hadronic Z decays into four jets. We find that the published OPAL data
from the 1991 and 1992 runs exclude a light quasi-stable gluino with mass
\lesssim 1.5 GeV/c^2 at more than 90% confidence level. This limit depends
little on assumptions about the gluino fragmentation and the definition of the
gluino mass. The exclusion confidence level is shown as a function of the mass.
A future projection is briefly discussed. We also discuss quantitatively how
the distributions in the Bengtsson-Zerwas and the modified Nachtmann-Reiter
angles change due to the finite bottom quark or gluino mass. The analysis is
limited to the leading-order calculations. We, however, give an empirical
reason to why the next-to-leading-order corrections are unlikely to change our
conclusions.


title:
Photon Structure Functions: Target Photon Mass Effects and QCD
  Corrections

abstract:
  We present a systematic analysis of the polarised and unpolarised processes
$e^+ ~e^- \rightarrow e^+ ~e^- X$ in the deep inelastic limit and study the
effects of target photon mass (virtuality) on the photon structure functions.
The effect of target photon virtuality manifests as new singly polarised
structure functions and also alters the physical interpretation of the
unpolarised structure functions. The physical interpretation of these structure
functions in terms of hadronic components is studied using the free field
analysis. We also retrieve the real photon results in the limit the virtuality
goes to zero. Assuming factorisation of the photon structure tensor, the
relevant QCD corrections to the various twist two structure functions are
evaluated.


title: Recent Results in the NJL model with heavy quarks

abstract:
  We investigate the interplay of chiral and heavy quark symmetries by using
the NJL quark model. Heavy quarks with finite masses m(Q) as well as the limit
m(Q) to infinity are studied. We found large corrections to the heavy mass
scaling law for the pseudoscalar decay constant. The influence of external
momenta on the shape parameters of the Isgur-Wise form factor is discussed.


title: Nucleosynthesis and the mass of the tau neutrino---ERRATUM

abstract:
  Our results for the primordial abundance of a massive Majorana tau neutrino
(hep-ph/9603201) published in PRL76, 2848 (1996) were incorrect due to a
trivial (but annoying) error in the numerical code. In this ERRATUM we present
the corrected results.


title: Photoproduction of jets at HERA

abstract:
  Recent NLO calculations for the photoproduction of one and two jets at HERA
are compared to data from H1 and ZEUS. We discuss the physics potential of
these measurements for constraining the photon structure, especially the quark
density at large $x$, and study remaining hadronization and jet definition
uncertainties.


title: Baryon Production in the String Fragmentation Picture

abstract:
  An improved version of the ``pop-corn'' model for baryon production in quark
and gluon jets is presented. With a reduced number of parameters the model
reproduces well both production rates for different baryon species and baryon
momentum distributions. Predictions are presented for a set of
baryon-antibaryon correlations.


title:
Heavy Baryon Chiral Perturbation Theory and the Spin 3/2 Delta
  Resonances

abstract:
  Heavy baryon chiral perturbation theory is briefly reviewed, paying
particular attention to the role of the spin 3/2 delta resonances. The concept
of resonance saturation for the baryonic sector is critically discussed.
Starting from a relativistic formulation of the pion-nucleon-delta system, the
heavy baryon chiral lagrangian including spin 3/2 resonances is constructed by
means of a 1/m-expansion. The effective theory obtained admits a systematic
expansion in terms of soft momenta, the pion mass $M_\pi$ and the delta-nucleon
mass difference $\Delta$.


title: Systematic 1/M Expansion for Spin 3/2 Particles

abstract:
  Starting from a relativistic formulation of the pion-nucleon-delta system,
the most general structure of 1/M corrections for a heavy baryon chiral
lagrangian including spin 3/2 resonances is given. The heavy components of
relativistic nucleons and delta fields are integrated out and their
contributions to the next-to-leaing order lagrangians are constructed
explicitly. The effective theory obtained admits a systematic expansion in
terms of soft momenta, the pion mass $m_\pi$ and the delta-nucleon mass
difference $\Delta$. As an application, we consider neutral pion
photoproduction at threshold to third order in this small scale expansion.


title: Isolated Prompt Photon Production at HERA

abstract:
  We study the expectations for prompt photon production rates at HERA in a
fully consistent next-to-leading order (NLO) QCD analysis, taking into account
the effects of experimental isolation requirements. In particular we examine
the sensitivity of the isolated cross section to the photon's gluon content.


title: Entropy production by resonance decays

abstract:
  We investigate entropy production for an expanding system of particles and
resonances with isospin symmetry -- in our case pions and $\rho$ mesons --
within the framework of relativistic kinetic theory. A cascade code to simulate
the kinetic equations is developed and results for entropy production and
particle spectra are presented.


title: Cool Pions move at less than the speed of light

abstract:
  At nonzero temperature, pions propagate through a thermal medium at less than
the speed of light. About low temperature, this effect begins not at $\sim
T^2$, but at next to leading order, $\sim T^4$. We also derive the
generalization of the relation of Gell-Mann, Oakes, and Renner to nonzero
temperature.


title: Charmonium Suppression by Comover Scattering in Pb+Pb Collisions

abstract:
  The first reports of $\psi$ and $\psi'$ production from experiment NA50 at
the CERN SPS are compared to predictions based on a hadronic model of
charmonium suppression. Data on centrality dependence and total cross sections
are in good accord with these predictions.


title: A New Approach to the Family Structure

abstract:
  In this letter, we introduce a new approach to formulate the family structure
of the standard model. Trying to mimic the highly contrained representation
structure of the standard model while extending the symmetry, we propose a
$SU(4)\otimes SU(3)\otimes SU(2)\otimes U(1)$ symmetry with a SM-like chiral
spectra basically "derived" from the gauge anomaly constraints. Embedding the
SM leads to $SU(4)_A\otimes SU(3)_C\otimes SU(2)_L\otimes U(1)_X$ models, which
upon the $SU(4)_A\otimes U(1)_X \longrightarrow U(1)_Y$ symmetry breaking,
gives the three families naturally as a result. A specific model obtained from
the approach is illustrated. The model, or others from our approach, holds
promise of a very interesting phenomenology. We sketch some of the results
here. An interesting possiblity of supersymmetrizing the model with the
EW-Higgses already in the spectrum is noted. A comparison with other approaches
is also discussed.


title: Color-Octet Charmonium Production in Top Quark Decays

abstract:
  We calculate the direct production rate of $J/\psi$ in top quark decays. The
color-octet $J/\psi$ production via $t\rightarrow W^+ b J/\psi$ is shown to
have a large branching ratio of order $1.5\times 10^{-4}$, which is over an
order of magnitude higher than that of the color-singlet $J/\psi$ production
via $t\rightarrow W^+ b J/\psi~g~g $ or $t\rightarrow W^+ b~\chi_{cJ}~g$
followed by $\chi_{cJ}\rightarrow J/\psi~\gamma$. This result can be used as a
powerful tool to test the importance of the color-octet mechanism in heavy
quarkonium production.


title: Cosmological Reheating and Self-Interacting Final State Bosons

abstract:
  We consider inflaton decay to final state bosons with self-interactions of
moderate strength. We find that such final state self-interactions
qualitatively alter the reheat dynamics. In the case of narrow-band resonance
decay, where a quantitative analysis is possible, we show that these final
state interactions regulate the decay rate. The phenomenon of parametric
amplification is then effectively suppressed, and does not drastically enhance
the decay rate and reheat temperature. Detailed applications of our results to
realistic classes of inflationary models will be considered elsewhere.


title: Tree-level (pi, K)-amplitude and analyticity

abstract:
  We consider the tree-level amplitude, describing all 3 channels of the binary
(pi ,K)-reaction, as a meromorphic polynomially bounded function of 3 dependent
complex variables. Relying systematically on the Mittag-Leffler theorem, we
construct 3 convergent partial fraction expansions, each one being applied in
the corresponding domain. Noting, that the mutual intersections of those
domains are nonempty, we realize the analytical continuation. It is shown that
the necessary conditions to make such a continuation feasible, are the
following: 1) The only parameters completely determining the amplitude are the
on-shell couplings and masses; 2) These parameters are restricted by a certain
(infinite) system of bootstrap equations; 3) The full cross-symmetric amplitude
takes the typically dual form, the Pomeron contribution being taken into
account; 4)This latter contribution corresponds to a nonresonant background,
which, in turn, is expressed in terms of cross-channel resonances parameters.
It is demonstrated also, that the Chiral Symmetry provides a unique scale for
the mentioned parameters, the resonance saturation effect appearing as a direct
consequence of the above results.


title:
On the possibility of measuring $F_L(x,Q^2)$ at HERA using radiative
  events

abstract:
  It is shown that a significant measurement of the longitudinal structure
function $F_L(x,Q^2)$ can be performed at HERA, for $Q^2 = 2 GeV^2$ and $Q^2 =
5 GeV^2$ and for x around $10^{-4}$, using radiative events with hard photon
emission collinear to the incident lepton beam, under the present running
conditions and with an integrated luminosity of 10 $pb^{-1}$. The influence of
experimental conditions is discussed.


title: Light Gluinos and Jet Production in $\bar p p$ Collisions

abstract:
  The impact of a light, long lived gluino on jet production cross sections in
$\bar p p$ collisions is estimated. The effect is found to be relatively
modest, particularly when gluinos are incorporated into the parton densities of
the proton. Although a light gluino does enhance the production of jets at high
$E_T$, the effect is insufficient, by itself, to explain the high $E_T$ excess
observed by CDF.


title: New Constraints on SO(10) Model-Building from String Theory

abstract:
  A recent analysis of the methods by which higher-level gauge symmetries are
realized in string theory has made it possible to systematically obtain new
constraints on string GUT model-building. In this paper, we perform such a
study for the case of SO(10) free-field string GUT models, and find a number of
significant new results. First, we show that within the conventional string
models using the so-called ``diagonal'' embeddings, all representations larger
than the 16 must always transform as singlets under all gauge symmetries beyond
SO(10). This includes the 45 and 54 representations, and holds regardless of
the affine level at which SO(10) is realized. Furthermore, we show that such
constructions can never give rise to the 120, 126, or 144 representations of
SO(10) --- again regardless of the affine level. We also perform a similar
analysis for E_6, and find that the adjoint 78 representation must always
transform as a singlet under all gauge symmetries beyond E_6; moreover, all
representations beyond the 78 representation are prohibited. Taken together,
these results thus severely limit the types of phenomenologically realistic
field-theoretic SO(10) and E_6 models that can be obtained using such string
constructions. Finally, we also explore the possibility of using non-diagonal
free-field embeddings, and show that in the SO(10) case such embeddings may
have improved phenomenological prospects.


title: The Heavy Quark Potential from Wilson's Exact Renormalization Group

abstract:
  We perform a calculation of the full momentum dependence of the gluon and
ghost propagators in pure SU(3) Yang-Mills theory by integrating Wilson's exact
renormalization group equations with respect to an infrared cutoff k. The heavy
quark potential in the quenched approximation can be expressed in terms of
these propagators. Our results strongly indicate a 1/p^4 behaviour of the heavy
quark potential for $p^2 \to 0$. We show in general, that effective actions
which satisfy Schwinger-Dyson equations, correspond to (quasi-) fixed points of
Wilson's exact renormalization group equations.


title: CP Violation in the B System

abstract:
  Strategies for extracting CKM phases from non-leptonic $B$ decays are
reviewed briefly. Both general aspects and some recent developments including
CP-violating asymmetries, the $B_s$ system in light of a possible width
difference $\Delta\Gamma_s$, and triangle relations among $B$ decay amplitudes
are discussed. The role of electroweak penguins in these strategies is
illustrated briefly.


title:
Charged-Meson Production and Scaling Violations of Fragmentation
  Functions in Deeply Inelastic Scattering at HERA

abstract:
  We compare recent experimental results for one-particle-inclusive processes
in deeply inelastic scattering at HERA with theoretical predictions in
next-to-leading-order QCD perturbation theory, and study the factorization
scale dependence of cross sections and charged multiplicities. In the future,
for the HERA machine running at design luminosity, scaling violations of
fragmentation functions permit the measurement of the strong coupling constant.
We estimate the size of the statistical error of $\alpha_s$ that can be
achieved, and study the theoretical error due to the various parton density
parametrizations and due to the factorization scale dependence.


title: Determination of pion-baryon coupling constants from QCD sum rules

abstract:
  We evaluate the pi-N-N, pi-Sigma-Sigma and pi-Sigma-Lambda coupling constants
using QCD sum rules based on pion-to-vacuum matrix elements of correlators of
two interpolating baryon fields. The parts of the correlators with Dirac
structure k-slash gamma_5 are used, keeping all terms up to dimension 5 in the
OPE and including continuum contributions on the phenomenological side. The
ratios of these sum rules to baryon mass sum rules yield stable results with
values for the couplings of g_{pi NN}=12+/-5, g_{pi Sigma Sigma}=7+/-4 and
g_{pi Sigma Lambda}=6+/-3. The sources of uncertainty are discussed.


title: Generating heavy quarkonia in a perturbative QCD cascade

abstract:
  We present an implementation of heavy quarkonium production within a
perturbative QCD cascade based on the Colour Dipole Cascade model. We consider
the processes most relevant in the context of the psi' surplus at the Tevatron;
g -> psi' and c -> psi' in the colour-singlet model and g -> psi' through the
colour-octet mechanism. Our implementation is, however, easily extendible to
other quarkonia and other production mechanisms. Where comparison is possible
we find good agreement with analytical calculations. We present some
suggestions for measurements at the Tevatron that would be sensitive to the
shape of the fragmentation functions. Our calculations indicate that such
measurements could be used to test the colour-octet mechanism solution to the
psi' surplus at the Tevatron.


title: Pion and Strangeness Puzzles

abstract:
  The dependence of pion and strangeness production on the number of
participant nucleons and collision energy is discussed for central A+A
collisions. A possible interpretation of the experimental results assuming
transition to QGP is sketched within a simple statistical approach.


title: QCD resummation and heavy quark cross sections

abstract:
  In this dissertation a detailed analysis of heavy quark production is given
with an emphasis on the resummation of soft gluon corrections. First we
calculate the production cross sections for top quark production at the
Fermilab Tevatron and for bottom quark production at fixed-target $pp$
experiments, and in particular HERA-B. We consider both the order $\alpha_s^3$
cross sections and the resummation of soft gluon corrections in all orders of
QCD perturbation theory. Then we calculate the inclusive transverse momentum
and rapidity distributions for top quark production at the Fermilab Tevatron
and bottom quark production at HERA-B. We give both $\alpha_s^3$ and resummed
results. Finally, we discuss the resummation of distributions that are singular
at the elastic limit of partonic phase space (partonic threshold) in QCD
hard-scattering cross sections, such as heavy quark production. We show how
nonleading soft logarithms exponentiate in a manner that depends on the color
structure within the underlying hard scattering. This result generalizes the
resummation of threshold singularities for the Drell-Yan process, in which the
hard scattering proceeds through color-singlet annihilation. We illustrate our
results for the case of heavy quark production by light quark annihilation and
gluon fusion, and also for light quark production through gluon fusion.


title: QCD, Strong CP and Axions

abstract:
  The physical origin of the strong CP problem in QCD, rooted in the structures
of the vacuum of the standard model, is reviewed. The chiral solution to this
problem, with its accompanying axion, is explained and various characteristics
of axions are detailed. Although visible axion models are excluded
experimentally, models with very light and very weakly coupled axions are still
tenable. The astrophysical and cosmological implications of such axion models
are discussed, along with ongoing experimental attempts to detect such, so
called, invisible axions.


title: Fluctuations and Bubble Dynamics in First-Order Phase Transitions

abstract:
  We numerically examine the effect of thermal fluctuations on a first-order
phase transition in 2+1 dimensions. By focusing on the expansion of a single
bubble we are able to calculate changes in the bubble wall's velocity as well
as changes in its structure relative to the standard case where the bubble
expands into a homogeneous background. Not only does the wall move faster, but
the transition from the symmetric to the asymmetric phase is no longer smooth,
even for a fairly strong transition. We discuss how these results affect the
standard picture of electroweak baryogenesis.


title: Measuring SUSY Parameters at LEP II Using Chargino Production and Decay

abstract:
  Previously, in the context of the minimal supersymmetric standard model
(without {\em a priori} assumptions of parameter unification), we studied the
constraints on weak-scale SUSY parameters from chargino production at LEP II,
using as observables $\mch$, $\mLSP$, the cross section and the leptonic
branching fraction. Here, exploiting the high degree of polarization in
chargino production, we add to our earlier work the forward-backward
asymmetries of the visible hadrons and leptons in chargino decays. For a
chargino that is mostly gaugino, the parameter space can now be restricted to a
small region; $\tanb$ is constrained, the soft electroweak gaugino and electron
sneutrino masses are determined to about 10\%, and the sign of $\mu$ may be
determined. Constraints for a chargino that is mostly Higgsino are much weaker,
but still disfavor the hypothesis that the chargino is mostly gaugino. For a
chargino which is a roughly equal mixture of Higgsino and gaugino, we find
intermediate results.


title: The meaning of anomalous couplings

abstract:
  A prescription is presented for the interpretation of the coefficients in an
effective lagrangian in terms of physical mass scales.


title:
Computational Advances in the Study of Baryon Number Violation in High
  Energy Electroweak Collisions

abstract:
  We present some recent advances in the computational study of baryon number
violation in high energy electroweak collisions. We examine classically allowed
processes above the sphaleron barrier and, using a stochastic search procedure,
we explore the topology changing region in the energy and particle number
plane. Finding topology changing classical solutions with small incident
particle number would be an indication that baryon number violation becomes
unsuppressed in high energy collisions. Starting with a topology changing
solution of approximately 50 incoming particles, our Monte-Carlo procedure has
produced other topology changing solutions with 40% lower incident particle
numbers, with energies up to one and a half times the sphaleron energy. While
these solutions still involve a rather large number of incident particles, we
have nonetheless demonstrated that our search procedure is effective in
reducing the particle number while ensuring topology change. Taking advantage
of more powerful computational resources, we plan to extend the search to still
higher energies.


title: Bound states of singlet quarks at LHC

abstract:
  We discuss the discovery potential of the bound states of singlet quarks at
LHC. We find that it is possible to discover bound states of singlet quarks at
LHC with singlet quark masses up to 300 Gev for $e_{Q} = \frac{2}{3}$ and up to
200 Gev for $e_{Q} = -\frac{1}{3}$.


title: Construction of a new constrained instanton in Yang-Mills-Higgs theory

abstract:
  A self-consistent ansatz is presented for a four-dimensional euclidean
solution (instanton) in the vacuum sector of constrained SU(2) Yang-Mills-Higgs
theory.


title: Mixing of neutral B mesons and factorization

abstract:
  A brief review of checking the factorization hypothesis for matrix element of
$B^0 - \bar B^0$ mixing within operator product expansion and QCD sum rules is
given. Both perturbative and power corrections are considered.


title: Effective linear meson model

abstract:
  The effective action of the linear meson model generates the mesonic n-point
functions with all quantum effects included. Based on chiral symmetry and a
systematic quark mass expansion we derive relations between meson masses and
decay constants. The model ``predicts'' values for f_eta and f_eta' which are
compatible with observation. This involves a large momentum dependent eta-eta'
mixing angle which is different for the on--shell decays of the eta and the
eta'. We also present relations for the masses of the 0^{++} octet. The
parameters of the linear meson model are computed and related to cubic and
quartic couplings among pseudoscalar and scalar mesons. We also discuss
extensions for vector and axialvector fields. In a good approximation the
exchange of these fields is responsible for the important nonminimal kinetic
terms and the eta-eta' mixing encountered in the linear meson model.


title:
Hadronic Vacuum Polarization Contribution to g-2 of the Leptons and
  alpha(M_Z)

abstract:
  We review and compare recent calculations of hadronic vacuum polarization
effects. In particular, we consider the anomalous magnetic moments g-2 of the
leptons and alpha(M_Z), the effective fine structure constant at the
Z--resonance.


title:
Deviations from the superposition model in a Dual Parton Model with
  formation zone cascade in both projectile and target nuclei

abstract:
  A Dual Parton Model with a formation zone intranuclear cascade in the
spectators of the projectile and target nuclei is studied. The hadrons produced
in the formation zone cascade contribute to Feynman-$x_F$ and lab-$x$
distributions in the fragmentation regions of the target and projectile nuclei.
We discuss the consequences of this model in the secondary cosmic ray
production, by analyzing the calculated spectrum weighted moments for pion and
kaon production. We show that the proposed model leads to significant
differences with respect to a simple superposition model, where the
nucleus-nucleus collision is replaced by a few corresponding nucleon-nucleus
collisions.


title:
The Oklo bound on the time variation of the fine-structure constant
  revisited

abstract:
  It has been pointed out by Shlyakhter that data from the natural fission
reactors which operated about two billion years ago at Oklo (Gabon) had the
potential of providing an extremely tight bound on the variability of the
fine-structure constant alpha. We revisit the derivation of such a bound by:
(i) reanalyzing a large selection of published rare-earth data from Oklo, (ii)
critically taking into account the very large uncertainty of the temperature at
which the reactors operated, and (iii) connecting in a new way (using isotope
shift measurements) the Oklo-derived constraint on a possible shift of thermal
neutron-capture resonances with a bound on the time variation of alpha. Our
final (95% C.L.) results are:
  -0.9 \times 10^{-7} <(alpha^{Oklo} - alpha^{now})/alpha <1.2\times 10^{-7}
  and -6.7 \times 10^{-17} {yr}^{-1} < {\dot alpha}^{averaged}/alpha
<5.0\times10^{-17} {yr}^{-1}$.


title:
Flavor Oscillations from a Spatially Localized Source: A Simple General
  Treatment

abstract:
  A unique description avoiding confusion is presented for all flavor
oscillation experiments in which particles of a definite flavor are emitted
from a localized source. The probability for finding a particle with the wrong
flavor must vanish at the position of the source for all times. This condition
requires flavor-time and flavor-energy factorizations which determine uniquely
the flavor mixture observed at a detector in the oscillation region; i.e. where
the overlaps between the wave packets for different mass eigenstates are almost
complete. Oscillation periods calculated for ``gedanken'' time-measurement
experiments are shown to give the correct measured oscillation wave length in
space when multiplied by the group velocity. Examples of neutrinos propagation
in a weak field and in a gravitational field are given. In these cases the
relative phase is modified differently for measurements in space and time.
Energy-momentum (frequency-wave number) and space-time descriptions are
complementary, equally valid and give the same results. The two identical phase
shifts obtained describe the same physics; adding them together to get a factor
of two is double counting.


title: Decays of a Leptophobic Gauge Boson

abstract:
  We discuss the theory and phenomenology of decays of a leptophobic $U(1)_\X$
gauge boson $X$, such as has been proposed to explain the alleged deviations of
$R_b$ and $R_c$ from standard model predictions. If the scalars involved in the
breaking of the $SU(2)\times U(1)$ symmetry are sufficiently light, $X$ will
sometimes decay into a charged (or neutral) scalar along with an
oppositely-charged $W$ (or $Z$). These decay modes could yield clean signals
for the leptophobic gauge bosons at hadron colliders and provide an interesting
window into the Higgs sector of the theory.


title:
The Klein-Gordon oscillator and the proper time formalism in a Rigged
  Hilbert sapace

abstract:
  The implications of manifestly covariant formulation of relativistic quantum
mechanics depending on a scalar evolution parameter, canonically conjugated to
the variable mass, is still an unsettled issue. In this work we find a complete
set of generalized eigenfunctions of the Klein-Gordon Oscillator in the above
mentioned formulation, in the Rigged Hilbert Space with Tempered
Ultradistributions. We briefly comment on some models where this solution could
be applied.


title:
Nucleon spin structure,topological susceptibility and the $\eta^\prime$
  singlet axial vector coupling

abstract:
  The observed small value of the first moment of the polarized nucleon spin
structure function $g_1$ may be interpreted, in the Veneziano--Shore approach,
as a suppression of the first moment $\chi^\prime(0)$ of the QCD topological
susceptibility. I give an extension of the Witten--Veneziano argument for the
$U(1)$ problem, which yields the $O(1/N)$ correction to the $N = \infty$
relation $\chi^\prime(0)/F^2_0 = 1$ (where $F_0$ is the $\eta^\prime$ axial
vector coupling).The correction, although negative, seems too small to account
for the data. I further argue that the
$(\eta,\eta^\prime)\rightarrow\gamma\gamma$ and $J/\psi\rightarrow (\eta ,
\eta^\prime)\gamma$ decays indicate an enhancement rather than a suppression of
$F_0$. A substantial gluon-like contribution in $\langle 0\vert\partial^\mu
j^{(0)}_{\mu_5} \vert\gamma\gamma \rangle \vert_{q^2=0}$,which could parallel a
similar one in the corresponding nucleon matrix element,is suggested.


title:
Comparison of Lattice and Chiral Perturbation Theory calculations of
  pion scattering lengths

abstract:
  I compare the lattice calculation of Fukugita et al. for the pion S-wave
scattering lengths to the predictions of Chiral Perturbation Theory to two loop
accuracy. I find good agreement, despite the use of the quenched approximation
in the lattice calculation.


title: Cancellation of infrared divergences at finite temperature

abstract:
  We consider a typical hard scattering process in a heat bath of photons and
electrons at temperature, $T$, in finite temperature QED. We show that, when
the hard scattering scale is much larger than the temperature, the infrared
pieces of both the real and virtual parts of the cross section factorise; these
can be exponentiated and cancel between each other to all orders in
perturbation theory. We use the technique of Grammer and Yennie to give a
prescription for the extraction of the infrared divergent parts, and for the
form of the finite remainder. Symmetry arguments are used to show the
finiteness of new terms arising in the $T \neq 0$ part of the computation.


title: Prominent Decay Modes of a Leptophobic Z'

abstract:
  An anomaly-free U(1) charge $Q'$ has recently been identified within the
group E$_6$ for which the familiar leptons (the left- and right-handed electron
and the left-handed neutrino) have $Q' = 0$. It is pointed out that the $Q'$
charges of several {\it exotic} leptons within E$_6$ matter multiplets are
quite large, leading to the prediction that half of the decays of the so-called
``leptophobic'' $Z'$ bosons coupling to $Q'$ are to these exotic leptons. Other
large $Q'$ charges include those of standard up-type quarks and exotic
down-type quarks. Substantial forward-backward asymmetries are expected in $u
\bar u \to Z' \to f \bar f$ channels when $f$ is a standard up-type quark, an
exotic down-type quark, or an exotic lepton.


title: Erratum for "Nucleosynthesis Constraints on Active-Sterile..."

abstract:
  The magnetization asymmetry given in eq. 3.6 of the above paper (ref. [1],
hep-ph/9402332) has a wrong relative sign between particle and anti-particle
contributions. Here we present the derivation of the correct sign and its
implications for the limits derived in [1]. This sign has also been recently
derived in a paper by Elmfors, Grasso and Raffelt, CERN-TH/96-88
[hep-ph/9605250] (ref. [2]) using a different method. While the sign error in
[1] does affect the nucleosynthesis bounds derived in [1], we would like to
stress that, in contrast to the criticism made in [2], it does not affect in
any way the conclusions reached in subsequent papers in S. Pastor, V. B.
Semikoz, J. W. F. Valle, Phys.Lett.B369 (1996) 301 and Astropart. Phys. 3
(1995) 87.


title: Salpeter amplitudes in a Wilson-loop context

abstract:
  The bound state problem for a gauge invariant quark-antiquark system is
considered in the instantaneous rest frame. Focus here is on the long range
non-perturbative interaction. A two-time Green's function is constructed for
Salpeter amplitudes. The corresponding Schr\"{o}dinger equation is found to be
in the Salpeter form with a Wilson-loop term as the instantaneous kernel.


title: Froissart boundary for deep inelastic structure functions

abstract:
  In this letter we derive the Froissart boundary in QCD for the deep inelastic
structure function in low $x$ kinematic region. We show that the comparison of
the Froissart boundary with the new HERA experimental data gives rise to a
challenge for QCD to explain the matching between the deep inelastic scattering
and real photoproduction process.


title:
Revisiting the Eichten - Feinberg - Gromes Q \bar{Q} Spin-Orbit
  Interaction

abstract:
  Invariant and covariant forms of the quark-antiquark interaction derived by
the method of Eichten and Feinberg are considered. Relations between the
various terms imposed by Lorentz transformation constraints, here called Gromes
relations, are found to exist in neither case. Details of the Gromes relation
proper are reconsidered and inconsistencies found that lead to a violation of
covariance.


title: Evidence for the Observation of a Glueball

abstract:
  I briefly review lattice QCD, the valence (quenched) approximation, and the
application of both to the determination of the mass and two-body decay
couplings of the lightest scalar glueball. Results in agreement with the
observed properties of $f_J(1710)$ strongly suggest this resonance is largely a
scalar glueball.


title: Low-Scale Technicolor at the Tevatron

abstract:
  In multiscale models of walking technicolor, relatively light color-singlet
technipions are produced in $q \ol q$ annihilation in association with
longitudinal $W$ and $Z$ bosons and with each other. The technipions decay as
$\tpiz \ra b \ol b$ and $\tpip \ra c \ol b$. Their production rates are
resonantly enhanced by isovector technirho vector mesons with mass $M_W +
M_{\tpi} \simle M_{\tro} \simle 2 M_{\tpi}$. At the Tevatron, these associated
production rates are 1--10 picobarns for $M_{\tpi} \simeq 100\,\gev$. Such a
low mass technipion requires topcolor-assisted technicolor to suppress the
decay $t \ra \tpip b$. Searches for $\tpi\tpi$ production will also be
rewarding. Sizable rates are expected if $M_{\tro} \simge 2M_{\tpi} +
10\,\gev$. The isoscalar $\omega_T$ is nearly degenerate with $\tro$ and is
expected to be produced at roughly the same rate. The $\omega_T$ should have
the distinctive decay modes $\omega_T \ra \gamma \tpiz$ and $Z \tpiz$.


title: Three-Scale Factorization Theorem and Effective Field Theory

abstract:
  We develop a perturbative QCD factorization theorem which is compatible with
effective field theory. The factorization involves three scales: an infrared
cutoff of order $\Lambda_{\rm QCD}$, a hard scale of order the $B$ meson mass,
and an ultraviolet cutoff of order the $W$ boson mass. Our approach is
renormalization group invariant and moderates the scale-dependence problem in
effective field theory. Applying this formalism to exclusive nonleptonic $B$
meson decays, we clarify the controversy over the Bauer-Stech-Wirbel parameters
$a_2/a_1$ for charm and bottom decays. It is found that the nonfactorizable
contribution plays an important role in the explanation of the sign and
magnitude of $a_2/a_1$.


title:
Photon--meson transition form factors $\gamma\pi^0$, $\gamma\eta$ and
  $\gamma\eta'$ at low and moderately high $Q^2$

abstract:
  We study photon--meson transition form factors $\gamma^*(Q^2)\gamma \to
\pi^0,\eta,\eta'$ at low and moderately high virtualities $Q^2$ of one of the
photons, the second photon being real. For the description of the form factor
at low $Q^2$, a nontrivial quark--antiquark $(q\bar q)$ structure of the photon
in the soft region is assumed, i.e. the photon is treated much like an ordinary
vector meson. At large $Q^2$, along with a perturbative tail of the soft wave
function, as it is for a hadron, the photon wave function contains also a
standard QED point-like $q\bar q$ component. The latter provides the $1/Q^2$
behavior of the transition form factor at large $Q^2$ in accordance with
perturbative QCD. Using the experimental results on $\gamma\pi^0$ form factor,
we reconstruct the soft photon wave function which is found to have the
structure similar to pion's, which has been formerly determined from a study of
the elastic pion form factor. Assuming the universality of the ground--state
pseudoscalar meson wave functions we calculate the transition form factors
$\gamma\eta$, $\gamma\eta'$ and partial widths $\eta\to\gamma\gamma$,
$\eta'\to\gamma\gamma$, in a perfect agreement with data.


title: Form factors of meson decays in constituent quark model

abstract:
  Meson decays are considered within the constituent quark model, making use of
the dispersion formulation of the model: Starting with spacelike momentum
transfers $q$, meson transition form factors are expressed as relativistic
invariant double spectral representations over the invariant masses of the
initial and final $Q\bar Q$ pairs. The form factors at timelike momentum
transfers are obtained by performing the analytical continuation in $q^2$. As a
result, the form factors both in the scattering and decay regions are expressed
through the light--cone wave functions of the initial and final hadrons. The
constituent quark transition form factor is briefly discussed.


title: An exact sum rule for transversely polarized DIS

abstract:
  The Operator Product Expansion provides expressions for the $n^{th}$ moments
of $g_1(x)$ and $g_2(x)$ in terms of hadronic matrix elements of local
operators for $n =$ odd integer. In some cases these matrix elements are
expected to be small leading to approximate sum rules for the {\em odd\/}
moments of $g_{1,2}(x)$. We have shown how, working in a field-theoretic
framework, one can derive expressions for the {\em even\/} moments of the {\em
valence\/} parts of $g_{1,2}(x)$. These expressions cannot be written as matrix
elements of {\em local\/} operators and do not coincide with the analytic
continuation to $n=$ even integer of the OPE results.
  Just as for the OPE one can in some cases argue that the hadronic matrix
elements should be small, leading to approximate sum rules for the moments of
the valence parts of $g_{1,2}(x)$. But, most importantly, for the case $n=2$ we
have proved rigorously that the hadronic matrix element vanishes, yielding the
exact ELT sum rule \int^1_0 dx\, x\left[g^V_1(x)+2g^V_2(x)\right]=0.
  We have argued that the convergence properties of this sum rule are good and
have discussed how it can be used to get information about $g_2(x)$ and as a
further test of QCD.


title: High Precision Tests of QED and Physics beyond the Standard Model

abstract:
  We study the four most significant high precision observables of QED ---the
anomalous electron and muon magnetic moments, the hydrogen Lamb shift and
muonium hyperfine splitting--- in the context of SU(2) x U(1) gauge-invariant
effective Lagrangians. The agreement between the theoretical predictions for
these observables and the experimental data places bounds on the lowest
dimension operators of the effective Lagrangians. We also place bounds on such
effective operators using other experimental data. Comparison of the tow types
of bounds allows us to discuss the potential of each one of the four high
precision observables in the search for physics beyond the Standard Model. We
find that the anomalous electron and muon magnetic moments are sensitive to new
physics while the hydrogen Lamb shift and muonium hyperfine splitting are not.


title:
Phase transition and nucleon as soliton in the Nambu-Jona-Lasinio model
  at finite temperature and density

abstract:
  We study some bulk thermodynamical characteristics, meson properties and the
nucleon as a baryon number one soliton in a hot quark matter in the NJL model
as well as in a hot nucleon matter in a hybrid NJL model in which the Dirac sea
of quarks is combined with a Fermi sea of nucleons. In both cases, working in
mean-field approximation, we find a chiral phase transition from Goldstone to
Wigner phase. At finite density the chiral order parameter and the constituent
quark mass have a non-monotonic temperature dependence - at finite temperatures
not close to the critical one they are less affected than in the cold matter.
Whereas the quark matter is rather soft against thermal fluctuations and the
corresponding chiral phase transition is smooth, the nucleon matter is much
stiffer and the chiral phase transition is very sharp. The thermodynamical
variables show large discontinuities which is an indication for a first order
phase transition. We solve the B=1 solitonic sector of the NJL model in the
presence of an external hot quark and nucleon medium. In the hot medium at
intermediate temperature the soliton is more bound and less swelled than in the
case of a cold matter. At some critical temperature, which for the nucleon
matter coincides with the critical temperature for the chiral phase transition,
we find no more a localized solution. According to this model scenario one
should expect a sharp phase transition from the nucleon to the quark matter.


title: A supergravity explanation of the CDF $ee\gamma\gamma$ event

abstract:
  We present a unified no-scale supergravity model with a light gravitino that
can naturally explain the observed $ee\gamma\gamma$ event at CDF via
right-handed selectron pair-production. The full spectrum of our model can be
described in terms of a single parameter and can be distinguished from
alternative proposals in the literature. Ongoing and future runs at LEP 2
should be able to probe the full allowed parameter space via acoplanar diphoton
events from $e^+e^-\to\chi^0_1\chi^0_1$ production.


title: Introduction to Structure Functions

abstract:
  The theory of deep inelastic scattering structure functions is reviewed with
an emphasis put on the QCD expectations of their behaviour in the region of
small values of the Bjorken parameter $x$.


title: Resummation in Heavy Quark and Jet Cross Sections

abstract:
  We discuss corrections from the elastic limit (partonic threshold) in
hadronic hard-scattering cross sections. We show why these corrections can be
large at all orders in perturbation theory, and describe their resummation to
arbitrary logarithmic accuracy. In particular, we discuss the role of color
exchange in the hard scattering. This enables us to generalize the resummation
of the Drell-Yan cross section to QCD reactions.
  As an example, we give the explicit resummed hard-scattering cross section
for heavy-quark production through light quark annihilation, which takes into
account next-to-leading logarithms to all orders.


title: The Polarized Two-loop Splitting Functions

abstract:
  We present a brief description of the light-cone gauge calculation of the
spin-dependent next-to-leading order splitting functions.


title: Wavelet Perspective of a Disoriented Chiral Condensate

abstract:
  The possible chiral phase transition in high energy heavy-ion collisions may
lead to the formation of a disoriented chiral condensate (DCC). However, the
existence of many uncorrelated small domains in the rather large interaction
volume and the huge combinatorial background make the experimental search for
the DCC signal a rather difficult task. We present a novel method for studying
the formation of a DCC in high energy heavy-ion collisions utilizing a discrete
wavelet transformation. We find the wavelet power spectrum for a DCC to exhibit
a strong dependence on the scale while an equilibrium system and the standard
dynamical models such as HIJING have a flat spectrum.


title: Dark Matter in Theories of Gauge-Mediated Supersymmetry Breaking

abstract:
  In gauge-mediated theories supersymmetry breaking originates in a strongly
interacting sector and is communicated to the ordinary sparticles via
SU(3)$\times$SU(2)$\times$U(1) carrying ``messenger'' particles. Stable baryons
of the strongly interacting supersymmetry breaking sector naturally weigh
$\sim$ 100 TeV and are viable cold dark matter candidates. They interact too
weakly to be observed in dark matter detectors. The lightest messenger particle
is a viable cold dark matter candidate under particular assumptions. It weighs
less than 5 TeV, has zero spin and is easily observable in dark matter
detectors.


title: Supernova Neutrino Energy Spectra and the MSW Effect

abstract:
  The distortions in the thermal energy spectra for neutrinos produced in a
supernova when a resonant oscillation, MSW effect, occurs are determined. In
order to show this effect for some relevant and representative examples of
unified gauge models, we have chosen $SO(10)$, and $SU(5)_{SUSY}$,
$SO(10)_{SUSY}$ with a particular scheme for fermion masses (DHR model). The
analysis has been performed for two choices of neutrinos parameters, predicted
by the above models, and capable to explain the solar neutrino problem. In both
cases one observes a strong distortion in the electron neutrino energy
spectrum. This effect, computed for a wide range of $SO(10)_{SUSY}$ models has
produced the same results of the previous supersymmetric ones.


title:
Implications of m_t and R_b on zt\bar{t} couplings in standard ETC
  models

abstract:
  In standard ETC models the sideways and diagonal ETC interactions contribute
to $\delta R_b$ with opposite signs. The aim of this article is to study the
implications of the CDF value for m_t and the LEP value for R_b on $zt\bar{t}$
couplings where the LH sideways and diagonal ETC effects interfere
constructively. We find that for m_t=175 Gev, $\delta R_b =.0022$ and
m^2_s=m^2_d, F^t_v and F^t_a are modified by 19% and 7% respectively from their
SM values. The constrains implied by these deviations on diagonal ETC scenarios
and the feasibility of probing them at NLC through polarization and angular
distribution studies in $e^+e^- \to t\bar{t}$ are also considered.


title: Small-Angle Bhabha Scattering

abstract:
  We present the calculation of the elastic and inelastic high--energy
small--angle electron--positron scattering with a {\it per mille} accuracy.
PACS numbers 12.15.Lk, 12.20.--m, 12.20.Ds, 13.40.--f


title: Evolution equation for gluon Regge trajectory

abstract:
  Analysing the asymptotic behaviour of the quark-quark elastic scattering
amplitude at high energy and fixed transferred momentum and assuming that gluon
is reggeized, we obtain the evolution equation for the gluon Regge trajectory
in QCD. It is closely related to the renormalization properties of the Wilson
lines and it is in a complete agreement with the recent results of two-loop
calculations.


title:
End-Point Behavior of Exclusive Processes: The Twilight Regime of
  Perturbative QCD

abstract:
  A selected set of topics along the borderline between perturbative and
nonperturbative QCD in exclusive reactions are studied. Specific problems,
related to different mechanisms of momentum transfer to an intact hadron, are
discussed. Calculations of the space-like form factors of the pion and the
nucleon are reviewed within a convolution scheme of short-distance (hard) and
large-distance (soft) contributions which takes into account soft gluon
emission and the intrinsic transverse hadron size. The failure of this scheme
to reproduce the existing experimental data signals sizeable higher-order
perturbative corrections (a K-factor of order two) and/or higher-twist
contributions.


title: String Unification and Leptophobic $Z'$ in Flipped SU(5)

abstract:
  We summarize recent developments in the prediction for $\alpha_s(M_Z)$,
self-consistent string unification and the dynamical determination of mass
scales, and leptophobic $Z'$ gauge bosons in the context of stringy flipped
SU(5). [To appear in Proceedings of Fourth International Conference on
Supersymmetry (SUSY96), University of Maryland (May 1996).]


title: The asymptotic behaviour of $F_{L}$ in the double scaling limit

abstract:
  In the kinematic region of small $x$ and large $Q^2$ in deep inelastic
scattering, presently being explored by HERA, we present an analysis of the
evolution of the longitudinal structure function $F_L^{p}(x, Q^2)$ in the
double scaling limit of Ball and Forte. We fit the evolution to a $1/x^\lambda$
behaviour and extract the value of $\lambda$. We also study the behaviour of
$R=F_2/2xF_1 -1$. We present comparisons of both $F_L$ and $R$ with the
corresponding MRS fits in this region of $x$ and $Q^2$.


title: Spectator Effects in the Heavy Quark Effective Theory

abstract:
  We present a complete analysis of the Heavy Quark Effective Theory Lagrangian
at order $1/m^2$ in the leading logarithmic approximation, including effects
induced by spectator quarks. At this order new correction terms appear in the
effective Lagrangian, as four-quark operators containing both heavy and light
quark fields. We compute the coefficients of these operators to one-loop order
and in the leading-logarithmic approximation. Two of them break the heavy quark
spin symmetry and we estimate their contribution to the hyperfine splitting of
the heavy mesons in the factorization approximation. We find that they make a
positive contribution to the hyperfine splitting of about 10% of the measured
splitting in the charm case and of up to 5% in the bottom case.


title:
Is the ee gamma gamma+ Missing E(T) Event an Evidence of the Light
  Axino?

abstract:
  We point out that if the Peccei-Quinn symmetry breaking scale $F_a$ is in a
range of the hadronic axion window ($F_a\sim 10^6$GeV), the
ee$\gamma\gamma+/\!\!\!\! E_T$ event in the CDF experiment can be naturally
explained by a no-scale supergravity model with a light axino. We also stress
that the hadronic axion window still survives the intergalactic photon search,
since a large entropy production due to the decay of Polonyi field yields a
substantial dilution of the cosmic axion density.


title: A Model-independent Way to Measure $|V_{ub}/V_{cb}|$

abstract:
  We propose a new model-independent method, to determine the ratio
$|V_{ub}/V_{cb}|$, which is theoretically described by the phase space factor
and the well-known perturbative QCD correction only. We explore the possible
experimental options: the measurement of inclusive hadronic invariant mass
distributions. We also discuss the relevant experimental backgrounds.


title: Color-octet heavy quarkonium productions in Z0 decays at LEP

abstract:
  We consider the energy and the polar angle distributions of J/\psi's produced
via the color-singlet and the color-octet (^3S_1^{(8)}) mechanisms in Z^0 \to
J/\psi +X at LEP. Since both distributions of the J/\psi produced via
color-octet mechanism are significantly different from those via color-singlet
mechanism, these observables can be used as tests of color-octet production
mechanism for heavy quarkonia. We also discuss Z^0 \rightarrow \Upsilon + X and
W \to J/\psi ( or \Upsilon) + X in brief.


title: Indirect Neutralino Detection Rates in Neutrino Telescopes

abstract:
  Neutralinos annihilating in the center of the Sun or the Earth may give rise
to a detectable signal of neutrinos. We derive the indirect detection rates for
neutrino telescopes in the minimal supersymmetric extension of the standard
model. We show that even after imposing all phenomenological and experimental
constraints that make the theories viable, regions of parameter space exist
which can already be probed by existing neutrino telescopes. We compare with
the discovery potential of supersymmetry at LEP2 as well as direct detections
and point out the complementarity of the methods.


title: Tracing QCD-Instantons in Deep Inelastic Scattering

abstract:
  We present a brief status report of our broad and systematic study of
QCD-instantons at HERA.


title: Percolation approach to Quark Gluon Plasma and $J/\psi$ suppression

abstract:
  It is shown that the critical threshold for percolation of the overlapping
strings exchanged in heavy ion collisions can naturally explain the sharp
strong suppresion of $J/\psi$ shown by the experimental data on central Pb--Pb
collisions, which does not occur in central O--U and S--U collisions.


title: Electroweak Parameters in the $\bar{MS}$-Scheme

abstract:
  We study electroweak parameters sensitive to the radiative corrections, such
as $\rho$-ratio and $\hff$ decay rates in the $\ms$-scheme in the heavy
$t$-quark mass limit $m_{t} \gg m_{w}$. In $\ms$-scheme the two-loop
electroweak corrections $\sim m_{t}^{4}$ dominate over the QCD corrections
$\sim \as m_{t}^{2}$ in the $\rho$-ratio. The relation between the on-shell
coupling constants and $\ms$-parameters is found to be rather sensitive to the
Higgs boson mass.


title: Probing Higgs Couplings in e^+ e^- \to \gamma\gamma\gamma

abstract:
  We investigate the existence of anomalous Higgs boson couplings,
$H\gamma\gamma$ and $HZ\gamma$, through the analysis of the process $e^+ e^-
\to \gamma\gamma\gamma$ at LEP2 energies. We suggest some kinematical cuts to
improve the signal to background ratio and determine the capability of LEP2 to
impose bounds on those couplings by looking for a Higgs boson signal in this
reaction.


title: On supersymmetry at high temperature

abstract:
  While it is possible to find examples of field theories with a spontaneously
broken symmetry at high temperature, in renormalizable supersymmetric models
any internal symmetry gets always restored. Recently, a counterexample was
suggested in the context of nonrenormalizable supersymmetric theories. We show
that non negligible higher loop effects actually restore the symmetry, without
compromising the validity of perturbation theory. We give some arguments as to
why the proposed mechanism should not work in general.


title: $B \to \rho \ell \nu_\ell$ Form Factors

abstract:
  The bounds on the form factors for $B \to \rho \ell \nu_\ell$ decay are
studied. Constrained by lattice data and a constrained conformal mapping, the
more informations can be obtained for $A_1(q^2)$ form-factor which dominates
the decay rate at large $q^2$. Specifically, we confirm a moderately increasing
behavior of this form factor.


title: Mixed quark-gluon condensate from instantons

abstract:
  We calculate the vacuum expectation value of the dimension-5 "mixed"
quark-gluon operator, $O_\sigma = \bar\psi (\lambda^a /2) \sigma_{\mu\nu} \psi
F_{\mu\nu}^a$, in the instanton vacuum. Within the $1/N_c$--expansion the QCD
operator is replaced by an effective many-fermion operator, which is averaged
over the effective theory of massive quarks derived from instantons. We find
$m_0^2 \equiv \langle O_\sigma \rangle / \langle \bar\psi\psi \rangle \approx 4
\bar\rho^{-2} = 1.4 GeV^2$, somewhat larger than the estimate from QCD sum
rules for the nucleon.


title:
On the analysis of the pion--nucleon $\sigma$--term: The size of the
  remainder at the Cheng--Dashen point

abstract:
  We calculate the one--loop contributions of order $M_\pi^4$ to the difference
$\Delta_R$ between the on--shell pion--nucleon scattering amplitude
$\bar{D}^+(0,2M_\pi^2)$ at the Cheng--Dashen point $\nu =0$, $t=2M_\pi^2$ and
the scalar form factor $\sigma (2M_\pi^2)$ in the framework of heavy baryon
chiral perturbation theory. We proof that to this order $\Delta_R$ contains
$no$ chiral logarithms and therefore it vanishes simply as $M_\pi^4$ in the
chiral limit. Numerically, we find as an upper limit $\Delta_R \simeq 2\,$MeV.


title: Q^2 evolution studies of nuclear structure function F_2 at HERA

abstract:
  Q**2 dependence of nuclear structure functions is important for understanding
perturbative QCD in nuclear environment. However, current experimental data are
not sufficient for studying nuclear dependence in the Q**2 evolution because
the data are limited in the small Q**2 region at small x. The future HERA
program can study the evolution in the large Q**2 region, and it provides us
crucial information on recombination effects and on higher-order alpha_s
effects in the nuclear structure functions.


title: Infrared modified analysis for the $\tau$ lepton width

abstract:
  We argue that accounting for higher order corrections in QCD by integrating a
running coupling constant through an infrared region can be most easily done
with making use of a scheme without the Landau pole. Within this approach the
entire ambiguity of the answer is identical to that of the choice of
renormalization scheme. The uncertainties for the $\tau$ lepton width resulting
from such a technique are discussed.


title: The $^{51}$Cr neutrino source and Borexino: a desirable marriage

abstract:
  Exposure to a $^{51}$Cr neutrino source as that used in Gallex will provide
an excellent overall performance test of Borexino, which should collect about
1400 source induced events, with an initial rate of about 35 counts per day.
This will be particularly important if MSW-small-angle turns out to be the
solution of the solar neutrino problem. In addition, if an independent,
accurate calibration is available, one will have an interesting experiment on
neutrino properties: as an example, a neutrino magnetic moment of the order
$5\cdot10^{-11}\mu_B$could be detected/excluded at the 90\% C.L.


title:
Relativistic Coulomb Problem: Energy Levels at the Critical Coupling
  Constant Analytically

abstract:
  The Hamiltonian of the spinless relativistic Coulomb problem combines the
standard Coulomb interaction potential with the square-root operator of
relativistic kinematics. This Hamiltonian is known to be bounded from below up
to some well-defined critical coupling constant. At this critical coupling
constant, however, the differences between all analytically obtainable upper
bounds on the corresponding energy eigenvalues and their numerically determined
(approximate) values take their maxima. In view of this, an analytical
derivation of (not so bad) upper bounds on the lowest-lying energy levels at
the critical coupling constant is presented.


title: Fermion Masses and Anti-grand Unification

abstract:
  We present an extension of the Standard Model (SM) without supersymmetry,
which we use to calculate order of magnitude values for the elements of the
mass matrices in the SM. In our model we can fit the 9 quark and lepton masses
and 3 mixing angles using only 3 free parameters, with the overall mass scale
set by the electroweak interaction. The specific model described here has the
anti-grand unified gauge group SMG^3 x U(1)_f at high energies where SMG =
SU(3) x SU(2) x U(1) is the SM gauge group. The SM fermions are placed in
representations of the full gauge group so that they do not produce any
anomalies.It is pointed out that the same results can be obtained in an anomaly
free SMG x U(1)^3 model.


title: Three-flavor atmospheric neutrino anomaly

abstract:
  We investigate the indications of flavor oscillations that come from the
anomalous flavor composition of the atmospheric neutrino flux observed in some
underground experiments. We study the information coming from the
neutrino-induced $\mu$-like and $e$-like events both in the sub-GeV energy
range (Kamiokande, IMB, Fr{\'e}jus, and NUSEX experiments) and in the multi-GeV
energy range (Kamiokande experiment). First we analyze all the data in the
limits of pure $\nu_\mu\leftrightarrow\nu_\tau$ and
$\nu_\mu\leftrightarrow\nu_e$ oscillations. We obtain that
$\nu_\mu\leftrightarrow\nu_e$ oscillations provide a better fit, in particular
to the multi-GeV data. Then we perform a three-flavor analysis in the
hypothesis of dominance of one neutrino square mass difference, $m^2$, implying
that the neutrino mixing is parametrized by two angles,
$(\psi,\,\phi)\in[0,\,\pi/2]$. We explore the space $(m^2,\,\psi,\,\phi)$
exhaustively, and find the regions favored by the oscillation hypothesis. The
results are displayed in a form suited to the comparison with other flavor
oscillation searches at accelerator, reactor, and solar $\nu$ experiments. In
the analysis, we pay particular attention to the earth matter effects, to the
correlation of the uncertainties, and to the symmetry properties of the
oscillation probability.


title: On the flavour dependence of polarized sea in the nucleon

abstract:
  We performed a phenomenological fit in order to get quark parton polarized
distributions in the nucleon. All data on inclusive and semi-inclusive spin
asymmetries measured on nucleon targets were used. We present the results for
the flavour dependence of polarized sea inside a nucleon. An excellent
agreement between inclusive and semi-inclusive data on polarized structure
functions was found in our model.


title: Analysis of the Z^0 Resonant Amplitude in General R_\xi Gauges

abstract:
  The Z^0 resonant amplitude is discussed in general R_\xi gauges. When the
original on-shell definition of the Z^0 mass M is employed, a gauge dependence
of M emerges in the next-to-leading approximation which, although small, is of
the same magnitude as the current experimental error. In the following order of
expansion, these unphysical effects are unbounded. The gauge dependence of M
disappears when modified, previously proposed definitions of mass or
self-energies, are used. The relevance of these considerations to the concept
of the mass of unstable particles is pointed out.


title: Status of the Proton Spin Problem

abstract:
  The proton spin problem triggered by the EMC experiment and its present
status are closely examined. Recent experimental and theoretical progresses and
their implications are reviewed. It is pointed out that the sign of the
sea-quark polarization generated perturbatively by hard gluons via the anomaly
mechanism is predictable: It is negative if the gluon spin component is
positive. We stress that the polarized nucleon structure function $g_1(x)$ is
independent of the $k_\perp$-factorization scheme chosen in defining the quark
spin density and the hard photon-gluon scattering cross section. Consequently,
the anomalous gluon and sea-quark interpretations for $\Gamma_1$, the first
moment of $g_1(x)$, are equivalent. It is the axial anomaly that accounts for
the observed suppression of $\Gamma_1^p$.


title: Dispersion Relations in Loop Calculations

abstract:
  These lecture notes give a pedagogical introduction to the use of dispersion
relations in loop calculations. We first derive dispersion relations which
allow us to recover the real part of a physical amplitude from the knowledge of
its absorptive part along the branch cut. In perturbative calculations, the
latter may be constructed by means of Cutkosky's rule, which is briefly
discussed. For illustration, we apply this procedure at one loop to the photon
vacuum-polarization function induced by leptons as well as to the $\gamma f\bar
f$ vertex form factor generated by the exchange of a massive vector boson
between the two fermion legs. We also show how the hadronic contribution to the
photon vacuum polarization may be extracted from the total cross section of
hadron production in $e^+e^-$ annihilation measured as a function of energy.
Finally, we outline the application of dispersive techniques at the two-loop
level, considering as an example the bosonic decay width of a high-mass Higgs
boson.


title: Resummation at Large $Q$ and at Small $x$

abstract:
  We propose a unified and simple viewpoint to various evolution equations
appropriate in different kinematic regions. We show that the resummation
technique reduces to the Altarelli-Parisi equation, if the transverse degrees
of freedom of a parton are ignored, to the Balitskii-Fadin-Kuraev-Lipatov
equation, if the momentum fraction of a parton vanishes, and to the
Gribov-Levin-Ryskin equation, if the recombination of gluons is included.


title: Multiparticle density matrix for the QCD-cascade in DLA approximation

abstract:
  The multiparton density matrices of the QCD gluon cascade are investigated.
The generating functional and master equation for momentum space multiparton
density in the double logarithmic approximation (DLA) are proposed.


title: Lattice Study of the Pomeron

abstract:
  We investigate the phenomenology of the Landshoff-Nachtmann
two-gluon-exchange model of the Pomeron using gluon propagators computed in the
Landau gauge within quenched lattice QCD simulations. As the propagators have
been evaluated entirely from QCD first principles, our results provide a
consistency check of the model. Finally, we report a proposal to investigate
the structure of the Pomeron-quark vertex, using a colour-singlet Pomeron
source constructed from the gauge fields.


title:
Higher-Order Hadronic Contributions to the Anomalous Magnetic Moment of
  Leptons

abstract:
  Higher-order hadronic contributions to the anomalous magnetic moment of the
electron, muon, and $\tau$ lepton are considered in detail. As a main result we
find a reduction by $-11 \times 10^{-11}$ for the g-2 of the muon as compared
to previous calculations. Analytical expressions for the kernel functions of
higher-order hadronic effects are presented. We employ the method of asymptotic
expansions to calculate kernel functions analytically in terms of a series
expansion in the lepton mass.


title: Coherent $\rho$ Production from Polarized Deuterium

abstract:
  We discuss the coherent leptoproduction of vector mesons from polarized
deuterium as a tool to investigate the evolution of small size quark-gluon
configurations. Kinematic regions are determined where the final state
interaction of the initially produced quark-gluon wave packet contributes
dominantly to the production cross section. Two methods for an investigation of
color coherence effects, which are appropriate for future experiments at
HERMES, are suggested.


title: A New Mechanism to Solve the Small Scale Problem of Local Supersymmetry

abstract:
  We extend the Standard Model gauge group by a a gauged $U(1)_R$ R-Symmetry or
a gauged $U(1)'$. The requirement of cancellation of anomalies is very
constraining but can be achieved by adding three or four hidden-sector fields
which are Standrad Model singlets. The $U(1)_R$ or $U(1)'$ quantum numbers of
these singlets are usually large producing a non-renormalisable superpotential
with a high power in the singelt fields. We have minimized the supergravity
scalar potential and have found solutions where the vacuum expectation values
of all hidden-sector singlet fields are less than the Planck mass
$<{z_m}>=O(M_{Pl}/10)$. This produces the small supersymmetry scale of order
the weak scale from only the Planck scale. The mu problem is simultaneously
solved in this manner.


title: On the twist-2 contributions to polarized structure functions

abstract:
  The twist--2 contributions to the polarized structure functions in deep
inelastic lepton--hadron scattering are calculated including the exchange of
weak bosons and using both the operator product expansion and the covariant
parton model. A new relation between two structure functions leading to a
sequence of new sum rules is found. The light quark mass corrections to the
structure functions are derived in lowest order QCD.


title:
Elastic Scattering and Transport Coefficients for a Quark Plasma in
  $SU_f(3)$ at Finite Temperatures

abstract:
  The temperature dependence of the elastic scattering processes $qq'\to qq'$
and $q\bar q'\to q\bar q'$, with $q, q' = u, d, s$ is studied as a function of
the scattering angle and the center of mass energy of the collision within the
framework of the $SU_f(3)$ Nambu--Jona--Lasinio model. Critical scattering at
threshold is observed in the $q\bar q'\to q\bar q'$ process, leading to an
enhancement of the cross section as occurs in the phenomenon of critical
opalescence. Transport properties such as viscosity, mean free paths and
thermal relaxation times are calculated. Strangeness enhancement is
investigated via the chemical relaxation times, which are found to be
considerably higher than those calculated via perturbative QCD. A comparison
with the experimental values for the strangeness enhancement in $S+S$
collisions leads to an upper limit of 4~fm/$c$ for the lifetime of the plasma.


title: What is the Brightest Source for Dilepton Emissions at RHIC?

abstract:
  We calculate the dilepton emissions as the decay product of the charm and
bottom quarks produced in heavy-ion collisions at RHIC energy. We take into
account the next-to-leading-order radiative corrections in perturbative QCD to
the heavy quark production from both an initial hard parton-parton scattering
and an ideal quark-gluon plasma. We find that the thermal charm decay dominates
the dilepton production in the low dilepton mass region ($<2$ GeV), while the
heavy quark production from the initial scattering takes over the intermediate
and high mass regions ($> 2$ GeV). Our result also indicates the importance of
the bottom quark in the high mass region ($>4 $ GeV ) due to its large mass and
cascade decay. If the initial scattering produced charm suffers a significant
energy loss due to the secondary interaction, the bottom decay constitutes the
major background for the thermal dileptons.


title: $J/\Psi$ and $\Psi '$ Suppression in Heavy Ion Collisions

abstract:
  We study the combined effect of nuclear absorption and final state
interaction with co-moving hadrons on the $J/\Psi$ and $\Psi '$ suppression in
proton-nucleus and nucleus-nucleus collisions. We show that reasonable
description of the experimental data can be achieved with theoretically
meaningful values of the cross-sections involved and without introducing any
dicontinuity in the $J/\Psi$ or $\Psi '$ survival probabilities.


title: Chiral poles and zeros and the role of the left hand cut

abstract:
  It has been recently claimed that the Inverse Amplitude Method provides a
reliable unitarisation of Chiral Perturbation Theory allowing resonance poles
to be accurately uncovered. We illustrate the sensitivity of these claims to
the treatment of the Adler zero and to assumptions about the left hand cut (and
hence about the underlying exchange forces). Previously favoured methods are
shown to mistreat the Adler zeros and violate crossing symmetry casting doubt
on the precision of their phenomenology. A more reliable solution is proposed.


title: Color Transparency Physics: A New Domain of Strong Interactions

abstract:
  The concept of color transparency is introduced. This new feature of QCD is
characteristic of a gauge theory. It enables strong interactions to be studied
in a new domain: scattering amplitudes of transversally small color singlet
objects. Experimental data are still few and somehow inconclusive. Future
prospects are briefly discussed. This is a frontier problem of QCD which
deserves much attention from both theorists and experimentalists in the coming
years.


title: Two Higgs Doublet Models

abstract:
  Present data do not rule out the light neutral Higgs particle $h$ or $A$ in
the framework of the general 2HDM. The discovery reach/exclusion limits of the
Yukawa process $Z\rightarrow f {\bar f} h/A$, ($f= b$ quark or $\tau$ lepton)
at LEP I and of the gluon-gluon fusion at HERA is discussed. In addition the
possible search for very light Higgs particle in $\gamma \gamma$ fusion at low
energy NLC is described.


title: CP-Violating Phases in the MSSM

abstract:
  We combine experimental bounds on the electric dipole moments of the neutron
and electron with cosmological limits on the relic density of a gaugino-type
LSP neutralino to constrain certain CP-violating phases appearing in the MSSM.
We find that in the Constrained MSSM, the phase |\theta_\mu | < \pi/10, while
the phase \theta_A remains essentially unconstrained.


title: Non-abelian Eikonals

abstract:
  A functional formulation and partial solution is given of the non-abelian
eikonal problem associated with the exchange of non-interacting, charged or
colored bosons between a pair of fermions, in the large $s$/small $t$ limit. A
simple, functional ``contiguity" prescription is devised for extracting those
terms which exponentiate, and appear to generate the leading, high-energy
behavior of each perturbative order of this simplest non-abelian eikonal
function; the lowest non-trivial order agrees with the corresponding SU(N)
perturbative amplitude, while higher-order contributions to this eikonal
generate an ``effective Reggeization" of the exchanged bosons, resembling
previous results for the perturbative amplitude. One exact and several
approximate examples are given, including an application to self-energy
radiative corrections. In particular, for this class of graphs and to all
orders in the coupling, we calculate the leading-log eikonal for SU(2). Based
on this result, we conjecture the form of the eikonal scattering amplitude for
SU(N).


title: Light Neutral Higgs Bosons at the Low Energy $\gamma \gamma $ Collider

abstract:
  A light neutral Higgs boson in the framework of the general two Higgs doublet
model (2HDM) is not excluded by existing data. We point out that it can be
looked for at the proposed low energy $\gamma \gamma$ collider. Failure to
detect one may lead to important limits on the parameters of the general 2HDM.


title:
Renormalizing the heavy quark effective field theory Lagrangian to order
  1/m^2

abstract:
  The heavy quark effective field theory Lagrangian is renormalized to order
1/m^2. Our technique eliminates operators that vanish by the equation of motion
by continuously redefining the heavy quark fields during renormalization. It is
consequently only necessary to calculate the running of the operators that do
not vanish by the equation of motion. Our results are found to be consistent
with reparameterization invariance.


title: Gravitino Warm Dark Matter Motivated by the CDF $ee\gamma\gamma $ Event

abstract:
  The $ee\gamma\gamma +\rlap/E_T$ event observed by the CDF at Fermilab is
naturally explained by dynamically supersymmetry breaking models and suggests
the presence of the light gravitino which can be a warm dark matter. We
consider large scale structure of the universe in the worm dark matter model
and find that the warm dark matter plays almost the same role in the formation
of the large scale structure as a cold dark matter if its mass is about
$0.5$keV. We also study the Ly~$\alpha$ absorption systems which are presumed
to be galaxies at high redshifts and show that the baryon density in the damped
Ly~$\alpha$ absorption systems predicted by the warm dark matter model is quite
consistent with the present observation.


title:
Dilepton asymmetries at $B$ factories in search of $\Delta B =- \Delta
  Q$ transitions

abstract:
  In order to detect the possible presence of $\Delta B = - \Delta Q$
amplitudes in neutral $B$ meson decays, we consider the measurement of decay
time asymmetries involving like-sign dilepton events at the $B$ factories.


title: QCD analysis of the CCFR data for $xF_3$ and Higher--Twist Contribution

abstract:
  The QCD analysis of the $xF_3$ structure function measured in deep-inelastic
scattering of neutrinos and antineutrinos on an iron target at the Fermilab
Tevatron is done in 1--, 2-- and 3--loop order of QCD. The x dependence of the
higher--twist contribution is evaluated. The experimental value of
higher--twist corrections to the Gross--Llewellyn Smith sum rule is discussed.


title: An Extension of the Electroweak Model with Decoupling at Low Energy

abstract:
  We present a renormalizable model of electroweak interactions containing an
extra $SU(2)'_L\otimes SU(2)'_R$ symmetry. The masses of the corresponding
gauge bosons and of the associated Higgs particles can be made heavy by tuning
a convenient vacuum expectation value. According to the way in which the heavy
mass limit is taken we obtain a previously considered non-linear model
(degenerate BESS) which, in this limit, decouples giving rise to the Higgsless
Standard Model (SM). Otherwise we can get a model which decouples giving the
full SM. In this paper we argue that in the second limit the decoupling holds
true also at the level of radiative corrections. Therefore the model discussed
here is not distinguishable from the SM at low energy. Of course the two models
differ deeply at higher energies.


title: Diquark model predictions for photon induced exclusive reactions

abstract:
  The present status of the diquark model for exclusive reactions at moderately
large momentum transfer is reviewed. That model is a variant of the
Brodsky-Lepage approach in which diquarks are considered as quasi-elementary
constituents of baryons. Recent applications of the diquark model, relevant to
high energy physics with electromagnetic probes, are discussed: electromagnetic
form factors of baryons in both the space-like and the time-like region,
photoproduction of mesons, two-photon annihilations into proton-antiproton
pairs as well as real and virtual Compton scattering on which the main emphasis
is laid.


title:
Gauge Couplings calculated from Multiple Point Criticality yield
  $\alpha^{-1}=136._8\pm 9$: At Last the Elusive Case of $U(1)$

abstract:
  We calculate the $U(1)$ continuum gauge coupling using the values of action
parameters at the multiple point in the phase diagram of a lattice gauge
theory. The multiple point is where a maximum number of phases convene. We
obtain for the running inverse finestructure constant the values
$\alpha_1^{-1}=56\pm 5$ and $\alpha_1^{-1}=99\pm 5$ at respectively the Planck
scale and the $M_Z$ scale. The gauge group underlying the phase diagram in
which we seek multiple point values of action parameters is what we call the
Anti Grand Unified Theory (AGUT) gauge group $SMG^3$ which is the Cartesian
product of 3 standard model groups (SMGs). There is one SMG factor for each of
the $N_{gen}=3$ generations of quarks and leptons. In our model, this gauge
group $SMG^3$ is the predecessor to the usual standard model group. The latter
arises as the diagonal subgroup surviving the Planck scale breakdown of $SMG^3.
This breakdown leads to a weakening of the $U(1)$ coupling by a
$N_{gen}$-related factor. The most important correction obtained from using
multiple point parameter values (in a multi-parameter phase diagram instead of
the single critical parameter value obtained say in the 1-dimensional phase
diagram of a Wilson action) comes from including the influence of having phases
confined solely w.r.t. discrete subgroups. In particular, what matters is that
the degree of first-orderness is taken into account in making the transition
from these latter phases at the multiple point to the totally Coulomb-like
phase. Combined with the results of earlier work on the non-Abelian gauge
couplings, the results presented here lead to our prediction of
$\alpha^{-1}=136._8\pm 9$ as the value for the fine-structure constant at low
energies.


title: Atmospheric neutrinos with three flavor mixing

abstract:
  We analyze the atmospheric neutrino data in the context of three flavor
neutrino oscillations taking account of the matter effects in the earth. With
the hierarchy among the vacuum mass eigenvalues $\mu_3^2 \gg \mu_2^2 \geq
\mu_1^2$, the solution of the atmospheric neutrino problem depends on
$\delta_{31}=\mu_3^2 - \mu_1^2$ and the $13$ and $23$ mixing angles $\phi$ and
$\psi$. Whereas the sub-GeV atmospheric neutrino data imposes only a lower
limit on $\delta_{31} > 10^{-3} eV^2$, the zenith angle dependent suppression
observed in the multi-GeV data limits $\delta_{31}$ from above also. The
allowed regions of the parameter space are strongly constrained by the
multi-GeV data. Combined with our earlier solution to the solar neutrino
problem which depends on $\delta_{21}= \mu_2^2-\mu_1^2$ and the $12$ and $13$
mixing angles $\omega$ and $\phi$, we have obtained the ranges of values of the
five neutrino parameters which solve both the solar and the atmospheric
neutrino problems simultaneously.


title: Quarkonia in Hamiltonian Light-Front QCD

abstract:
  A constituent parton picture of hadrons with logarithmic confinement
naturally arises in weak coupling light-front QCD. Confinement provides a mass
gap that allows the constituent picture to emerge. The effective renormalized
Hamiltonian is computed to ${\cal O}(g^2)$, and used to study charmonium and
bottomonium. Radial and angular excitations can be used to fix the coupling
$\alpha$, the quark mass $M$, and the cutoff $\Lambda$. The resultant hyperfine
structure is very close to experiment.


title: Non-decoupling and lepton number violation in left-right models

abstract:
  We argue that large non-decoupling effects of heavy neutrinos can appear
naturally in manifestly left-right symmetric models due to the minimization
conditions of the scalar potential and the structure of vev's imposed by
phenomenology. We derive constraints on off-diagonal light-heavy and
heavy-heavy neutrino mixings from the searches for lepton violating decays
$\mu\rightarrow e\gamma,$ $\mu\rightarrow e e^-e^+$ and $\mu-e$ conversion in
nuclei. The most stringent limits come from the latter process because its
amplitude shows a quadratic non-decoupling dependence on the heavy neutrino
mass. Due to the suppression of right-handed currents by large $W_R$ mass the
present experiments are not sensitive to the intergenerational mixings between
heavy neutrinos if $M_{W_R}>200$ TeV.


title: Corrections of Order $\alpha^6m$ to $S$-Levels of Helium

abstract:
  Several new corrections of order $m\alpha^6$ to the energy levels of $S$
states in helium are obtained from radiative corrections to the Breit potential
and from the polarization insertions in the two photon exchange graphs. While
individual gauge invariant contributions are comparable to current experimental
errors, the sum of these corrections is an order of magnitude smaller due to
mutual cancellations.


title: MS bar Perturbation Theory and the Higgs Boson Mass

abstract:
  We show that MS bar perturbation theory develops tachyonic singularities for
some value of the dimensional regularization scale mu unless the physical Higgs
mass exceeds some (cutoff dependent) minimum value.


title:
Form factor relations for heavy-to-heavy and heavy-to-light meson
  transitions

abstract:
  Relations between the form factors that parametrize the hadronic matrix
elements, in spectator decays of heavy mesons, have been derived by Stech
within the constituent quark model. In here, we examine these relations using a
slightly modified description of the meson states. We find new and very general
relations for some of the form factors. For the other form factors, we obtain
small modifications to the relations previously derived by Stech, in the case
of heavy-to-light transitions.


title:
Suppression of J/psi and Psi' Production in High-Energy Pb on Pb
  Collisions

abstract:
  The anomalous J/psi suppression in Pb-Pb collisions at 158A GeV observed
recently by NA50 can be explained as due to the transition to a new phase of
strong J/psi absorption, which sets in when the local energy density exceeds
about 3.4 GeV/fm**3.


title: Global Fits of the SM and MSSM to Electroweak Precision Data

abstract:
  The Minimal supersymmetric extension of the Standard Model (MSSM) with light
stops, charginos or pseudoscalar Higgs bosons has been suggested as an
explanation of the too high value of the branching ratio of the Z0 boson into b
quarks (Rb anomaly). A program including all radiative corrections to the MSSM
at the same level as the radiative corrections to the SM has been developed and
used to perform global fits to all electroweak data from LEP, SLC and the
Tevatron. The probability of the global fit improves from 8% in the SM to 18%
in the MSSM. Including the b->s gamma rate, as measured by CLEO, reduces the
probability from 18% to 15%. In the constrained MSSM requiring unification and
electroweak symmetry breaking no improvement of Rb is possible.


title: Color and charge breaking minima in the MSSM

abstract:
  The scalar potential of theories with broken supersymmetry can have a number
of local minima characterized by different gauge groups. Symmetry properties of
the physical vacuum constrain the parameters of the MSSM. We discuss these
constraints, in particular those that result from the vacuum stability with
respect to quantum tunneling.


title:
$b \bar b W^+ W^-$ production at hadron colliders. Top signal and
  irreducible backgrounds

abstract:
  We compute complete tree level matrix elements for $gg , q \bar q \rightarrow
b \bar b W^+W^-$. We analyze the irreducible backgrounds to top signal at the
Tevatron and at the LHC. Their contribution to the total cross section is about
$5 \%$ at the LHC, due to single resonant channels. Several distributions with
contributions from signal and backgrounds are presented.


title: Inclusive Measurement of the Strong Coupling at HERA

abstract:
  We describe the measurement of the strong coupling alpha_s from data on
inclusive DIS at high energies. We present new results using the 1994 data from
H1, and confirm directly the expected running of alpha_s.


title: Gluon Radiation in Diffractive Electroproduction

abstract:
  Order $\alpha_s$-corrections to the diffractive structure functions $F_L^D$
and $F_2^D$ at large $Q^2$ and small $x$ are evaluated in the semiclassical
approach, where the initial proton is treated as a classical colour field. The
diffractive final state contains a fast gluon in addition to a quark-antiquark
pair. Two of these partons may have large transverse momentum. Our calculations
lead to an intuitive picture of deep-inelastic diffractive processes which is
very similar to Bjorken's aligned-jet model. Both diffractive structure
functions contain leading twist contributions from high-$p_{\perp}$ jets.


title: Double scaling violations

abstract:
  We discuss the theoretical implications of the scaling properties of F_2^p at
small x observed in recent HERA experiments. We show that low Q^2 data display
double scaling violations which are adequately described by NL ln Q^2
corrections. Scaling violations due to summations of leading and subleading ln
1/x beyond NLO in ln Q^2 are however disfavoured by the data.


title: Supersymmetric Dark Matter in the Light of LEP 1.5

abstract:
  We discuss the lower limit on the mass of the neutralino $\chi$ that can be
obtained by combining data from $e^+e^-$ annihilation at LEP and elsewhere with
astrophysical and theoretical considerations. Loopholes in the purely
experimental analysis of ALEPH data from the Z peak and LEP 1.5, which appear
when $\mu<0$ for certain values of the sneutrino mass $m_{\tilde\nu}$ and the
ratio $\tan\beta$ of supersymmetric Higgs vacuum expectation values, may be
largely or totally excluded by data from lower-energy $e^+e^-$ data, the
hypothesis that most of the cosmological dark matter consists of $\chi$
particles, and the assumption that electroweak symmetry breaking is triggered
by radiative corrections due to a heavy top quark. The combination of these
inputs imposes $m_{\chi} \ge 21.4~\gev$, if soft supersymmetry-breaking masses
are assumed to be universal at the grand-unification scale.


title: Decay constants of P and D-wave heavy-light mesons

abstract:
  We investigate decay constants of P and D-wave heavy-light mesons within the
mock-meson approach. Numerical estimates are obtained using the relativistic
quark model. We also comment on recent calculations of heavy-light
pseudo-scalar and vector decay constants.


title: What is the Scale of Supersymmetry Breaking

abstract:
  For a long time, it has been widely assumed that if the underlying laws of
nature are supersymmetric, supersymmetry is broken at a scale intermediate
between the weak scale and the Planck mass. The construction of realistic
models of dynamical supersymmetry breaking in which supersymmetry is broken at
a much lower scale, as well as a growing appreciation of the supersymmetric
flavor problem has reopened this question. After reviewing some ideas for
understanding the microscopic origin of the soft breaking parameters in the
context of string theory, I turn to low energy breaking. Independent of the
details of the underlying theory, events with photons and missing energy, like
the CDF $e^+e^-\gamma \gamma \not{E}_T$ event, are likely signals of low energy
breaking. I briefly review the predictions of the simplest model of low energy
supersymmetry breaking for the soft breaking parameters (MGM), and then ask
what sorts of generalizations are possible. It turns out that if all couplings
are weak, there are only a limited number of ways to modify the model.


title:
Combining exclusive semi-leptonic and hadronic B decays to measure
  |V_ub|

abstract:
  The Cabibbo-Kobayashi-Maskawa matrix element |V_ub| can be extracted from the
rate for the semi-leptonic decay B -> pi + l + antineutrino_l, with little
theoretical uncertainty, provided the hadronic form factor for the B -> pi
transition can be measured from some other B decay. In here, we suggest using
the decay B -> pi J\psi. This is a color suppressed decay, and it cannot be
properly described within the usual factorization approximation; we use instead
a simple and very general phenomenological model for the b d J\psi vertex. In
order to relate the hadronic form factors in the B -> pi J\psi and B -> pi + l
+ antineutrino_l decays, we use form factor relations that hold for
heavy-to-light transitions at large recoil.


title:
A low energy dynamical SUSY breaking scenario motivated from superstring
  derived unification

abstract:
  Recently there has been a resurgence of interest in gauge mediated dynamical
supersymmetry breaking scenarios. I investigate how low energy dynamical SUSY
breaking may arise from superstring models. In a three generation string
derived model I propose that the unbroken hidden non--Abelian gauge group at
the string scale is $SU(3)_H$ with matter multiplets. Due to the small gauge
content of the hidden gauge group the supersymmetry breaking scale may be
consistent with the dynamical SUSY breaking scenarios. The messenger states are
obtained in the superstring model from sectors which arise due to the
``Wilson--line'' breaking of the unifying non--Abelian gauge symmetry. An
important property of the string motivated messenger states is the absence of
superpotential terms with the Standard Model states. The stringy symmetries
therefore forbid the flavor changing processes which may arise due to couplings
between the messenger sector states and the Standard Model states. Motivated
from the problem of string gauge coupling unification I contemplate a scenario
in which the messenger sector consists solely of color triplets. This
hypothesis predicts a chargino mass below the $W$--boson mass. Imposing the
current limits from the LEP1 and LEP1.5 experiments the lightest supersymmetric
particles predicted by this hypothesis are in the mass ranges
$M_{\chi^\pm}\approx55-65$ GeV, $M_{\chi^0}\approx35-50$ GeV and
$M_{\tilde\nu}\approx45-60$ GeV which will be tested in the forthcoming LEP2
experiments.


title:
Mass and width of sigma(750) scalar meson from measurements of
  piN->pi(-)pi(+)N on polarized targets

abstract:
  The measurements of reactions $\pi^- p_\uparrow \to \pi^- \pi^+ n$ at 17.2
GeV/c and $\pi^+ n_\uparrow \to \pi^+ \pi^- p$ at 5.98 and 11.85 GeV/c made at
CERN with polarized targets provide a model-independent and
solution-independent evidence for a narrow scalar state sigma(750). The
original chi^2 minimization method and the recent Monte Carlo method for
amplitude analysis of data at 17.2 GeV/c are in excellent agreement. Both
methods find that the mass distribution of the measured amplitude $|\overline S
|^2\Sigma$ with recoil transversity ``up'' resonates near 750 MeV while the
amplitude $|S|^2\Sigma$ with recoil transversity ``down'' is large and
nonresonating. The amplitude $|S|^2\Sigma$ contributes as a strong background
to S-wave intensity I_S = (|S|^2 + |\overline S |^2)\Sigma$ and distorts the
determinations of $\sigma$ resonance parameters from $I_S$. To avoid this
problem we perform a series of Breit-Wigner fits directly to the measured
distribution $|\overline S |^2\Sigma$. The inclusion of various backgrounds
causes the width of sigma(750) to become very narrow. Our best fit with
$t$-averaged coherent background yields $m_\sigma = 753 \pm 19$ MeV and
$\Gamma_\sigma = 108 \pm 53$ MeV. These values are in excellent agreement with
Ellis-Lanik theorem for the width of scalar gluonium. The gluonium
interpretation of $\sigma(750)$ is also supported by the absence of
$\sigma(750)$ in reactions $\gamma\gamma \to \pi\pi$. We also show how data on
polarized target invalidate essential assumptions of past determinations of
$\pi\pi$ phase shifts .


title: Supersymmetric Framework for a Dynamical Fermion Mass Hierarchy

abstract:
  We propose a new framework for constructing supersymmetric theories of
flavor, in which flavor symmetry breaking is triggered by the dynamical
breakdown of supersymmetry at low energies. All mass scales in our scheme are
generated from the supersymmetry breaking scale $\Lambda_{SSB} \approx 10^7$
GeV through radiative corrections. We assume a spontaneously broken flavor
symmetry and the Froggatt-Nielsen mechanism for generating the fermion Yukawa
couplings. Supersymmetry breaking radiatively induces a vacuum expectation
value for a scalar field, which generates invariant masses for the
Froggatt-Nielsen fields at $M_F \approx 10^4$ GeV. `Flavon' fields $\varphi$,
which spontaneously break the flavor symmetry, naturally acquire negative
squared masses due to two-loop diagrams involving the Froggatt-Nielsen fields,
and acquire vacuum expectation values of order $\langle \varphi \rangle \approx
M_F/16\pi^2$. The fermion mass hierarchy arises in our framework as a power
series in the ratio $\langle \varphi \rangle / M_F \approx 1/16\pi^2$.


title: Effective Theory for Heavy Quarkonia Decays

abstract:
  An effective theory approach to heavy quarkonia decays based on the $1/m_Q$
expansion is introduced. Its application to decays in which the two heavy
quarks annihilate is discussed.