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In the minimal supersymmetric standard model (MSSM), when radiative
corrections are included, the mass of the $CP=+1$ lightest Higgs boson is
bounded by $\sim 110\ GeV$ for $m_t < 150\ GeV$ and a scale of supersymmetry
breaking $\sim\ 1\ TeV$. In non-minimal supersymmetric standard models (NMSSM)
upper bounds on the mass of the corresponding scalar Higgs boson arise if the
theory is required to remain perturbative up to scales $\gg G_F^{-1/2}$. We
have computed those bounds for two illustrative NMSSM: i) A model with an
arbitrary number of gauge singlets; ii) A model with three $SU(2)_L$ triplets
with $Y=0,\pm 1$. We have integrated numerically the corresponding
renormalization group equations (RGE), including the top and bottom quark
Yukawa couplings, and added one-loop radiative corrections. For $m_t > 91\ GeV$
the absolute bounds are $\sim 140\ GeV$ for both models.
|
hep-ph/9208226
| 727,424 |
We find the precise relationship between the loop gas method and the matrix
quantum mechanics approach to two-dimensional string theory. The two systems
are distinguished by different target spaces ($\Z$ and $\R$, respectively) as
far as {\it observables} are concerned. We argue that target space loop
correlators should coincide in the two models and demonstrate this for a number
of examples. As a consequence some interesting generic observations about the
structure of two-dimensional string theory may be made: Restricting to a
discrete target space leads to {\it factorization} of amplitudes and thus to
very simple sewing rules. It is also demonstrated that the restriction to the
discrete target space still allows to calculate the correlation functions of
tachyon operators in the unrestricted theory.
|
hep-th/9208042
| 727,424 |
We present a mechanism in which models with two Higgs fields can undergo a
two stage phase transition as the temperature falls. The first stage is a
conventional second order (or weakly first order) transition in which the
symmetry is broken. Shortly thereafter follows a first order transition with
barrier penetration, bubble production and loss of thermal equilibrium. For
Higgs potentials with CP violation, we show that the second stage of the
transition has all the features required for weak scale baryogenesis.
|
hep-ph/9208227
| 727,424 |
Conformal fields are a new class of $Vect(N)$ modules which are more general
than tensor fields. The corresponding diffeomorphism group action is
constructed. Conformal fields are thus invariantly defined.
|
hep-th/9208043
| 727,425 |
We propose a simple discrete model to study the nonequilibrium fluctuations
of two locally coupled 1+1 dimensional systems (interfaces). Measuring
numerically the tilt-dependent velocity we construct a set of stochastic
continuum equations describing the fluctuations in the model
The scaling predicted by the equations are studied analytically using dynamic
renormalization group and compared with simulation results. When the coupling
is symmetric, the well known KPZ exponents are recovered. If one of the systems
is fluctuating independently, an increase in the roughness exponent is observed
for the other one.
|
cond-mat/9208010
| 727,425 |
In some spin tunneling problems, there are several different but
symmetry-related tunneling paths that connect the same initial and final
configurations. The topological phase factors of the corresponding tunneling
amplitudes can lead to destructive interference between the different paths, so
that the total tunneling amplitude is zero. In the study of tunneling between
different ground state configurations of the Kagom\'{e}-lattice quantum
Heisenberg antiferromagnet, this occurs when the spin $s$ is half-odd-integer.
|
cond-mat/9208011
| 727,425 |
Recently, a method was proposed and tested to find saddle points of the
action in simulations of non-abelian lattice gauge theory. The idea, called
`extremization', is to minimize $\int(\dl S/\dl A_\mu)^2$. The method was
implemented in an explicitly gauge variant way, however, and gauge dependence
showed up in the results.
Here we show how extremization can be formulated in a way that preserves
gauge invariance on the lattice. The method applies to any gauge group and any
lattice action. The procedure is worked out in detail for the standard
plaquette action with gauge groups U(1) and SU(N).
|
hep-lat/9208013
| 727,426 |
We introduce {\it conformal multi-matrix models} (CMM) as an alternative to
conventional multi-matrix model description of two-dimensional gravity
interacting with $c < 1$ matter. We define CMM as solutions to (discrete)
extended Virasoro constraints. We argue that the so defined alternatives of
multi-matrix models represent the same universality classes in continuum limit,
while at the discrete level they provide explicit solutions to the
multi-component KP hierarchy and by definition satisfy the discrete
$W$-constraints. We prove that discrete CMM coincide with the $(p,q)$-series of
2d gravity models in a {\it well}-{\it defined} continuum limit, thus
demonstrating that they provide a proper generalization of Hermitian one-matrix
model.
|
hep-th/9208044
| 727,427 |
Right-handed neutrinos with large Majorana mass occur naturally in the
left-right symmetric model. We explore the prospect of such heavy Right-handed
Neutrino search Via $W_R$ decay in the Like Sign Dilepton channel at SSC/LHC.
The standard model background can be effectively eliminated by suitable lepton
$p_T$ and isolation cuts without affecting the signal cross section seriously.
In this way it seems possible to explore the bulk of the parameter space $0 <
M_{N_R} < M_{W_R}$, with $M_{W_R}$ going upto 3000 (2000) GeV at SSC (LHC)
energy.
|
hep-ph/9208228
| 727,427 |
Computations in Dynamical Triangulation Models of Four-Dimensional Quantum
Gravity involve weighted averaging over sets of all distinct triangulations of
compact four-dimensional manifolds. In order to be able to perform such
computations one needs an algorithm which for any given $N$ and a given compact
four-dimensional manifold $M$ constructs all possible triangulations of $M$
with $\leq N$ simplices. Our first result is that such algorithm does not
exist. Then we discuss recursion-theoretic limitations of any algorithm
designed to perform approximate calculations of sums over all possible
triangulations of a compact four-dimensional manifold.
|
hep-lat/9208014
| 727,428 |
We study the phenomenology and cosmology of the Majoron (flavon) models of
three active and one inert neutrino paying special attention to the possible
(almost) conserved generalization of the Zeldovich-Konopinski-Mahmoud lepton
charge. Using Planck scale physics effects which provide the breaking of the
lepton charge, we show how in this picture one can incorporate the solutions to
some of the central issues in neutrino physics such as the solar and
atmospheric neutrino puzzles, dark matter and a 17 keV neutrino. These
gravitational effects induce tiny Majorana mass terms for neutrinos and
considerable masses for flavons. The cosmological demand for the sufficiently
fast decay of flavons implies a lower limit on the electron neutrino mass in
the range of 0.1-1 eV.
|
hep-ph/9208230
| 727,428 |
We show that the BF theory in any space-time dimension, when quantized in a
certain linear covariant gauge, possesses a vector supersymmetry. The generator
of the latter together with those of the BRS transformations and of the
translations form the basis of a superalgebra of the Wess-Zumino type. We give
a general classification of all possible anomalies and invariant counterterms.
Their absence, which amounts to ultraviolet finiteness, follows from purely
algebraic arguments in the lower-dimensional cases.
|
hep-th/9208047
| 727,428 |
We examine the behavior of the standard-model electroweak phase transition in
the early Universe. We argue that close to the critical temperature it is
possible to estimate the {\it effective} infrared corrections to the 1-loop
potential using well known $\varepsilon$-expansion results from the theory of
critical phenomena in 3 spatial dimensions. The theory with the
$\varepsilon$-corrected potential exhibits much larger fluctuations in the
spatial correlations of the order parameter, considerably weakening the
strength of the transition.
|
hep-ph/9208231
| 727,429 |
Gravitational instantons, solutions to the euclidean Einstein equations, with
topology $R^3 XS^1$ arise naturally in any discussion of finite temperature
quantum gravity. This Letter shows that all such instantons (irrespective of
their interior behaviour) must have the same asymptotic structure as the
Schwarzschild instanton. Using this, it can be shown that if the Ricci tensor
of the manifold is non-negative it must be flat. One special case is when the
Ricci tensor vanishes; hence one can conclude that there is no nontrivial
vacuum gravitational instanton. This result has uses both in quantum and
classical gravity. It places a significant restriction on the instabilities of
hot flat space. It also can be used to show that any static vacuum Lorentzian
Kaluza-Klein solution is flat.
|
gr-qc/9208007
| 727,429 |
The effect of collective potentials on pion spectra in ultrarelativistic
heavy ion collisions is investigated. We find the effect of these potential to
be very small, too small to explain the observed enhancement at low transverse
momenta. (7 figures, bill be send on request)
|
hep-ph/9208232
| 727,429 |
Within a wide class of ferromagnetic and antiferromagnetic systems, quantum
tunneling of magnetization direction is spin-parity dependent: it vanishes for
magnetic particles with half-integer spin, but is allowed for integer spin. A
coherent-state path integral calculation shows that this topological effect
results from interference between tunneling paths.
|
cond-mat/9208012
| 727,429 |
We have observed the production of strings (disclination lines and loops) via
the Kibble mechanism of domain (bubble) formation in the isotropic to nematic
phase transition of a sample of uniaxial nematic liquid crystal. The probablity
of string formation per bubble is measured to be $0.33 \pm 0.01$. This is in
good agreement with the theoretical value $1/ \pi$ expected in two dimensions
for the order parameter space $S^2/{\bf Z}_2$ of a simple uniaxial nematic
liquid crystal.
|
hep-ph/9208233
| 727,429 |
This article gives necessary and sufficient conditions for the formation of
trapped surfaces in spherically symmetric initial data defined on a closed
manifold. Such trapped surfaces surround a region in which there occurs an
enhancement of matter over the average. The conditions are posed directly in
terms of physical variables and show that what one needs is a relatively large
amount of excess matter confined to a small volume. The expansion of the
universe and an outward flow of matter oppose the formation of trapped
surfaces; an inward flow of matter helps. The model can be regarded as a
Friedmann-Lema\^\i tre-Walker cosmology with localized spherical
inhomogeneities. We show that the total excess mass cannot be too large.
|
gr-qc/9208008
| 727,429 |
We study non-perturbatively, via the Schwinger-Dyson equations, the leading
infrared behavior of the pressure in the ladder approximation. This problem is
discussed firstly in the context of a thermal scalar field theory, and the
analysis is then extended to the Yang-Mills theory at high temperatures. Using
the Feynman gauge, we find a system of two coupled integral equations for the
gluon and ghost self-energies, which is solved analytically. The solutions of
these equations show that the contributions to the pressure, when calculated in
the ladder approximation, are finite in the infrared domain.
|
hep-ph/9208234
| 727,429 |
We present a superconformally invariant and integrable model based on the
twisted affine Kac-Moody superalgebra $\hat{osp(2|2)}^{(2)}$ which is the
supersymmetrization of the purely bosonic conformal affine Liouville theory
recently proposed by Babelon and Bonora. Our model reduces to the
super-Liouville or to the super sinh-Gordon theories under certain limit
conditions and can be obtained, via hamiltonian reduction, from a superspace
WZNW model with values in the corresponding affine KM supergroup. The
reconstruction formulae for classical solutions are given. The classical
$r$-matrices in the homogeneous grading and the exchange algebras are worked
out.
|
hep-th/9208048
| 727,429 |
A method is derived for calculating the pairing kernel in exchange mediated
superconductors including matrix element effects. Various models for the
interaction vertex are considered, including spin exchange, orbital exchange,
and quadrupolar exchange. As an example, this formalism is applied to $UPt_3$
using relativistic wavefunctions from a local density band calculation.
|
cond-mat/9208013
| 727,429 |
We consider the possibility of using the hierarchical approximation to
understand the continuum limit of a reformulation of the 3D Ising model
initiated by Polyakov. We introduce several new formulations of the
hierarchical model using dual or fermionic variables. We discuss several
aspects of the renormalization group transformation in terms of these new
variables. We mention a reformulation of the model closely related to string
models proposed by Zabrodin.
|
hep-th/9208050
| 727,430 |
It is proved that for a system of spins $\sigma _i = \pm 1$ having an
interaction energy $-\sum K_{ij} \sigma _i \sigma _j $ with all the $K_{ij}$
strictly positive,one can construct a dual formulation by associating a dual
spin $S_{ijk} = \pm 1$ to each triplet of distinct sites $i,j$ and $k$. The
dual interaction energy reads $-\sum _{(ij)} D_{ij} \prod _{k \neq i,j}
S_{ijk}$ with $tanh(K_{ij})\ = \ exp(-2D_{ij})$, and it is invariant under
local symmetries. We discuss the gauge-fixing procedure, identities relating
averages of order and disorder variables and representations of various
quantities as integrals over Grassmann variables. The relevance of these
results for Polyakov's approach of the 3D Ising model is briefly discussed.
|
hep-lat/9208015
| 727,430 |
We survey the present trends in theory of universal arrows to forgetful
functors from various categories of topological algebra and functional analysis
to categories of topology and topological algebra. Among them are free
topological groups, free locally convex spaces, free Banach-Lie algebras, and
much more. An accent is put on relationship of those constructions with other
areas of mathematics and their possible applications. A number of open problems
is discussed; some of them belong to universal arrow theory, and others may
hopefully become amenable to methods of this theory.
|
funct-an/9208001
| 727,430 |
We derive a formula for the nonequilibrium entropy of a classical stochastic
field in terms of correlation functions of this field. The formalism is then
applied to define the entropy of gravitational perturbations (both
gravitational waves and density fluctuations). We calculate this entropy in a
specific cosmological model (the inflationary Universe) and find that on scales
of interest in cosmology the entropy in both density perturbations and
gravitational waves exceeds the entropy of statistical fluctuations of the
microwave background. The nonequilibrium entropy discussed here is a measure of
loss of information about the system. We discuss the origin of the entropy in
our cosmological models and compare the definition of entropy in terms of
correlation functions with the microcanonical definition in quantum statistical
mechanics.
|
gr-qc/9208009
| 727,430 |
Let $X$ denote an integral, projective Gorenstein curve over an algebraically
closed field $k$. In the case when $k$ is of characteristic zero, C. Widland
and the second author have defined Weierstrass points of a line bundle on $X$.
In the first section, this definition is extended to linear systems in
arbitrary characteristic. This definition may be viewed as a generalization of
the definitions of Laksov and St\"ohr-Voloch to the Gorenstein case. In the
second section, an example is given to illustrate the definition. This example
is a plane curve of arithmetic genus 3 in characteristic 2 such that the gap
sequence at every smooth point (with respect to the dualizing bundle) is 1,2,5
and there are no smooth Weierstrass points. In the third section, the
Weierstrass weight of a unibranch singularity (on a not necessarily rational
curve) is computed in terms of its semigroup of values. In the final section,
the Weierstrass weight of a singularity with precisely two branches (again
assuming that the characteristic is zero) is computed.
AMS Classification: Primary 14H55, Secondary 14H20.
|
alg-geom/9208003
| 727,430 |
All experimental results concerning possible neutrino oscillations are
naturally and simultaneously accounted for in an $E_6$ GUT model. The fermionic
mass matrices are dictated by the symmetry breaking and specific radiative
corrections and not by the use of ``Ans\"atze'' or discrete symmetries.
|
hep-ph/9208235
| 727,430 |
We consider the design of a non-local MonteCarlo algorithm for $SU(3)$
lattice systems according to the idea of {\em embedding} the degrees of freedom
corresponding to the center of the group $Z(3)$. As a crucial ingredient to
reach this goal, we present a practical implementation of a cluster algorithm
for $Z(3)$ systems with general random pair interaction.
|
hep-lat/9208016
| 727,430 |
A new electron focusing effect has been discovered in small single and
coupled GaAs/AlGaAs rings. The focusing in the single ring is attributed solely
to internal orbits. The focusing effect allows the ring to be used as a small
mass spectrometer. The focusing causes peaks in the magnetoresistance at low
fields, and the peak positions were used to study the dispersion relation of
the one-dimensional magnetoelectric subbands. The electron effective mass
increases with the applied magnetic field by a factor of $50$, at a magnetic
field of $0.5T$. This is the first time this increase has been measured
directly. General agreement obtains between the experiment and the subband
calculations for straight channels.
|
cond-mat/9208014
| 727,430 |
Older lattice work exploring the Higgs mass triviality bound is briefly
reviewed. It indicates that a strongly interacting scalar sector in the minimal
standard model cannot exist; on the other hand low energy QCD phenomenology
might be interpreted as an indication that it could. We attack this puzzle
using the $1/N$ expansion and discover a simple criterion for selecting a
lattice action that is more likely to produce a heavy Higgs particle. Depending
on the precise form of the limitation put on the cutoff effects, our large $N$
calculations, when combined with old numerical data, suggest that the Higgs
mass bound might be around 750 $GeV$, which is higher than the $\sim 650~GeV$
previously obtained. Preliminary numerical work indicates that an increase of
at least 19\% takes place at $N=4$ on the $F_4$ lattice when the old simple
action is replaced with a new action (still containing only nearest neighbor
interactions) if one uses the lattice spacing as the physical cutoff for both
actions. It appears that, while a QCD like theory could produce $M_H / F ~ \sim
6$, a meaningful ``minimal elementary Higgs'' theory cannot have $M_H/ F~
\gtapprox 3$. Still, even at 750 $GeV$, the Higgs particle is so wide ($\sim
290~$GeV), that one cannot argue any more that the scalar sector is weakly
coupled.
|
hep-lat/9208017
| 727,430 |
We compute the hyperfine splitting $m_{J/\psi}-m_{\eta_c}$ on the lattice,
using both the Wilson and $O(a)$-improved (clover) actions for quenched quarks.
The computations are performed on a $24^3\times48$ lattice at $\beta = 6.2$,
using the same set of 18 gluon configurations for both fermion actions. We find
that the splitting is 1.83\err{13}{15} times larger with the clover action than
with the Wilson action, demonstrating the sensitivity of the spin-splitting to
the magnetic moment term which is present in the clover action. However, even
with the clover action the result is less than half of the physical
mass-splitting. We also compute the decay constants $f_{\eta_c}$ and
$f^{-1}_{J/\psi}$, both of which are considerably larger when computed using
the clover action than with the Wilson action. For example for the ratio
$f^{-1}_{J/\psi}/f^{-1}_{\rho}$ we find 0.32\err{1}{2} with the Wilson action
and $0.48\pm 3$ with the clover action (the physical value is 0.44(2)).
|
hep-lat/9208018
| 727,431 |
The reduced tension $\sigma_{cd}$ of the interface between the confined and
the deconfined phase of $SU(3)$ pure gauge theory is related to the finite size
effects of the first transfer matrix eigenvalues. A lattice simulation of the
transfer matrix spectrum at the critical temperature $T_c = 1/L_t$ yields
$\sigma_{cd} = 0.139(4) T_c^2$ for $L_t = 2$. We found numerical evidence that
the deconfined-deconfined domain walls are completely wet by the confined
phase, and that the confined-deconfined interfaces are rough.
|
hep-lat/9208020
| 727,431 |
An algoritm for the simulation of the 3--dimensional random field Ising model
with a binary distribution of the random fields is presented. It uses
multi-spin coding and simulates 64 physically different systems simultaneously.
On one processor of a Cray YMP it reaches a speed of 184 Million spin updates
per second. For smaller field strength we present a version of the algorithm
that can perform 242 Million spin updates per second on the same machine.
|
hep-lat/9208019
| 727,431 |
Non-compact lattice QED with two flavors of light dynamical quarks is
simulated on $16^4$ lattices, and the chiral condensate, monopole density and
susceptibility and the meson masses are measured. Data from relatively high
statistics runs at relatively small bare fermion masses of 0.005, 0.01, 0.02
and 0.03 (lattice units) are presented. Three independent methods of data
analysis indicate that the critical point occurs at $\beta =0.225(5)$ and that
the monopole condensation and chiral symmetry breaking transitions are
coincident. The monopole condensation data satisfies finite size scaling
hypotheses with critical indices compatible with four dimensional percolation.
The best chiral equation of state fit produces critical exponents
($\delta=2.31$, $\beta_{mag}=0.763$) which deviate significantly from mean
field expectations. Data for the ratio of the sigma to pion masses produces an
estimate of the critical index $\delta$ in good agreement with chiral
condensate measurements. In the strong coupling phase the ratio of the meson
masses are $M_\sigma^2/M_\rho^2\approx 0.35$, $M_{A_1}^2/M_\rho^2\approx 1.4$
and $M_\pi^2/M_\rho^2\approx 0.0$, while on the weak coupling side of the
transition $M_\pi^2/M_\rho^2\approx 1.0$, $M_{A_1}^2/M_\rho^2\approx 1.0$,
indicating the restoration of chiral symmetry.\footnote{$\,^{}$}{August 1992}
|
hep-lat/9208021
| 727,431 |
A free non-relativistic particle moving in two dimensions on a half-plane can
be described by self-adjoint Hamiltonians characterized by boundary conditions
imposed on the systems. The most general boundary condition is parameterized in
terms of the elements of an infinite-dimensional matrix. We construct the
Brownian functional integral for each of these self-adjoint Hamiltonians.
Non-local boundary conditions are implemented by allowing the paths striking
the boundary to jump to other locations on the boundary. Analytic continuation
in time results in the Green's functions of the Schrodinger equation satisfying
the boundary condition characterizing the self-adjoint Hamiltonian.
|
hep-th/9208052
| 727,431 |
Four-fermi models in dimensionality $2<d<4$ exhibit an ultra-violet stable
renormalization group fixed point at a strong value of the coupling constant
where chiral symmetry is spontaneously broken. The resulting field theory
describes relativistic fermions interacting non-trivially via exchange of
scalar bound states. We calculate the $O(1/N_f)$ corrections to this picture,
where $N_f$ is the number of fermion species, for a variety of models and
confirm their renormalizability to this order. A connection between
renormalizability and the hyperscaling relations between the theory's critical
exponents is made explicit. We present results of extensive numerical
simulations of the simplest model for $d=3$, performed using the hybrid Monte
Carlo algorithm on lattice sizes ranging from $8^3$ to $24^3$. For $N_f=12$
species of massless fermions we confirm the existence of a second order phase
transition where chiral symmetry is spontaneously broken. Using both direct
measurement and finite size scaling arguments we estimate the critical
exponents $\beta$, $\gamma$, $\nu$ and $\delta$. We also investigate symmetry
restoration at non-zero temperature, and the scalar two-point correlation
function in the vicinity of the bulk transition. All our results are in
excellent agreement with analytic predictions, and support the contention that
the $1/N_f$ expansion is accurate for this class of models.
|
hep-lat/9208022
| 727,431 |
In the context of the left-right symmetric gauge group [SU(6)]$^3\times$
Z$_3$ which unifies nongravitational forces with flavors, we analyze the
generational seesaw mechanism. At tree level we get
m$_{\nu_\tau}\sim$m$_{\nu_\mu}\sim$M$^2_L$/M$_H$, m$_{\nu_e}=0$, where
M$_L\sim10^2$ GeVs and M$_H\ge 100$ TeVs is the mass scale at which the
horizontal interactions get spontaneously broken. The right handed neutrinos
get a Majorana mass M$_R\gg $M$_H$ of the order of the scale where SU(2)$_R$ is
broken. An exotic neutral lepton with a mass of the order of M$^2_H$/M$_R$ is
predicted. First order radiative corrections will produce m$_{\nu_e}\neq0$
which is at least two orders of magnitude smaller than the other two neutrino
masses.
|
hep-ph/9208236
| 727,431 |
We investigate the renormalization of ``nonlocal" interactions which arise as
an infinite sum of higher derivative interactions in an effective field theory.
Using dimensional regularization with minimal subtraction in a general scalar
field theory, we write an integro-differential renormalization group equation
for the most general graph at one loop order.
|
hep-ph/9208237
| 727,431 |
The $\Sigma_c^*-\Sigma_c$ and $\Sigma_b^*-\Sigma_b$ hyperfine mass splittings
are computed in the Skyrme model. The hyperfine splittings are suppressed by
both $1/N_c$ and by $1/m_Q$, where $N_c$ is the number of colors and $m_Q$ is
the mass of the heavy quark. The $\Sigma_c$, $\Sigma_c^*$, $\Sigma_b$,
$\Sigma_b^*$, and $\Lambda_b$ masses are predicted in terms of the known values
of the $\Lambda_c$, $D$, $D^*$, $B$ and $B^*$ masses.
|
hep-ph/9208238
| 727,431 |
The models of triangulated random surfaces embedded in (extended) Dynkin
diagrams are formulated as a gauge-invariant matrix model of Weingarten type.
The double scaling limit of this model is described by a collective field
theory with nonpolynomial interaction.
The propagator in this field theory is essentially two-loop correlator in the
corresponding string theory.
|
hep-th/9208053
| 727,431 |
According to string/fivebrane duality, the Green-Schwarz factorization of the
$D=10$ spacetime anomaly polynomial $I_{12}$ into $X_4\, X_8$ means that just
as $X_4$ is the anomaly polynomial of the $d=2$ string worldsheet so $X_8$
should be the anomaly polynomial of the $d=6$ fivebrane worldvolume. To test
this idea we perform a fivebrane calculation of $X_8$ and find perfect
agreement with the string one--loop result.
|
hep-th/9208055
| 727,431 |
The cold dark matter (CDM) model of structure formation, normalized on large
scales, leads to excessive pairwise velocity dispersions on small scales. In an
attempt to circumvent this problem, we study three scenarios (all with
$\Omega=1$) which have more large-scale power and less small-scale power than
the CDM model: 1) an admixture of cold and hot dark matter; 2) cold dark matter
with a non-scale-invariant, power-law primordial power spectrum; and 3) cold
dark matter with coupling of dark matter to a long-range vector field. Despite
the {reduced} small-scale power, when such models are evolved in the nonlinear
regime to large amplitude, the velocities on small scales are actually {\it
increased} over CDM with the same value of $\sigma_8$. This `flip-over', in
disagreement with the expectation from linear perturbation theory, arises from
the nonlinear coupling of the extra power on large scales with shorter
wavelengths. However, due to the extra large-scale power, the recent COBE DMR
results indicate smaller amplitudes for these models, $\sigma_8 \sim 0.5 -
0.7$, than for CDM (for which $\sigma_8 \sim 1.2$). Therefore, when normalized
to COBE on large scales, such models do lead to reduced velocities on small
scales and they produce fewer halos compared with CDM. Quantitatively it seems,
however, that models that produce sufficiently low small-scale velocities fail
to produce an adequate distribution of halos.
|
hep-ph/9208239
| 727,431 |
Using dimensional regularization for both infrared and ultraviolet
divergences, we confirm that the QCD corrections to the decay width
$\Gamma(t\to H^+b)$ are equal to those to $\Gamma(t\to W^+b)$ in the limit of a
large $t$ quark mass.
|
hep-ph/9208240
| 727,431 |
Let S be a torsion section of an elliptic surface with only I_n fibers. This
article addresses the question: which components of singular fibers can S pass
through? We give necessary criteria for the "component numbers", and show an
equidistribution result for torsion sections of prime order.
|
alg-geom/9208004
| 727,431 |
We report tests of finite-size scaling ansatzes in the low temperature phase
of the two-dimensional Ising model. For moments of the magnetisation density,
we find good agreement with the new ansatz of Borgs and Koteck\'y, and clear
evi consequences of the convexity of the free energy are not adequately treated
in either of these approaches.\lb {\it Keywords}\/: Finite-size scaling, 2-d
Ising, pure-phase susceptibility.
|
hep-lat/9208024
| 727,432 |
Quantization of the dilaton gravity in two dimensions is discussed by a
semiclassical approximation. We compute the fixed-area partition function to
one-loop order and obtain the string susceptibility on Riemann surfaces of
arbitrary genus. Our result is consistent with the approach using techniques of
conformal field theories.
|
hep-th/9208056
| 727,433 |
Using Hirota's method, solitons are constructed for affine Toda field
theories based on the simply-laced affine algebras. By considering
automorphisms of the simply-laced Dynkin diagrams, solutions to the remaining
algebras, twisted as well as untwisted, are deduced.
|
hep-th/9208057
| 727,434 |
The tau-function formalism for a class of generalized ``zero-curvature''
integrable hierarchies of partial differential equations, is constructed. The
class includes the Drinfel'd-Sokolov hierarchies. A direct relation between the
variables of the zero-curvature formalism and the tau-functions is established.
The formalism also clarifies the connection between the zero-curvature
hierarchies and the Hirota-type hierarchies of Kac and Wakimoto.
|
hep-th/9208058
| 727,434 |
The 1-loop anomalies of a d-dimensional quantum field theory can be computed
by evaluating the trace of the regulated path integral jacobian matrix, as
shown by Fujikawa. In 1983, Alvarez-Gaum\'e and Witten observed that one can
simplify this evaluation by replacing the operators which appear in the
regulator and in the jacobian by quantum mechanical operators with the same
(anti)commutation relations. By rewriting this quantum mechanical trace as a
path integral with periodic boundary conditions for a one-dimensional
supersymmetric nonlinear sigma model, they obtained the chiral anomalies for
spin 1/2 and 3/2 fields and selfdual antisymmetric tensors in d dimensions. In
this article, we treat the case of trace anomalies for spin 0, 1/2 and 1 fields
in a gravitational and Yang-Mills background. We do not introduce a
supersymmetric sigma model, but keep the original Dirac matrices $\g^\m$ and
internal symmetry generators $T^a$ in the path integral. As a result, we get a
matrix-valued action. Gauge covariance of the path integral then requires a
definition of the exponential of the action by time-ordering. We exponentiate
the factors $\sqrt g$ in the path integral measure by using vector ghosts in
order to exhibit the cancellation of the sigma model divergences more clearly.
We compute the trace anomalies in d=2 and d=4.
|
hep-th/9208059
| 727,434 |
We study the signals for composite vector leptoquarks in $e^+ e^-$ colliders
(LEP II, NLC, and CLIC) through their effects on the production of jet pairs,
as well as their single and pair productions. We also analyze their production
in $\gamma e$ and $\gamma\gamma$ collisions.
|
hep-ph/9208242
| 727,434 |
A framework for predicting charged fermion masses in supersymmetric grand
unified theories is extended to make predictions in the neutrino sector. Eight
new predictions are made, and their relevance to neutrino oscillation
experiments and the solar neutrino problem are discussed.
|
hep-ph/9208243
| 727,434 |
We study representations of Temperley-Lieb algebras associated with the
transfer matrix formulation of statistical mechanics on arbitrary lattices. We
first discuss a new hyperfinite algebra, the Diagram algebra
$D_{\underline{n}}(Q)$, which is a quotient of the Temperley-Lieb algebra
appropriate for Potts models in the mean field case, and in which the algebras
appropriate for all transverse lattice shapes $G$ appear as subalgebras. We
give the complete structure of this subalgebra in the case ${\hat A}_n$ (Potts
model on a cylinder). The study of the Full Temperley Lieb algebra of graph $G$
reveals a vast number of infinite sets of inequivalent irreducible
representations characterized by one or more (complex) parameters associated to
topological effects such as links. We give a complete classification in the
${\hat A}_n$ case where the only such effects are loops and twists.
|
hep-th/9208061
| 727,434 |
The order-disorder duality structure is exploited in order to obtain a
quantum description of anyons and vortices in: a) the Maxwell theory; b) the
Abelian Higgs Model; c) the Maxwell-Chern-Simons theory; d) the
Maxwell-Chern-Simons-Higgs theory. A careful construction of a charge bearing
order operator($\sigma$) and a magnetic flux bearing disorder operator (vortex
operator) ($\mu$) is performed, paying attention to the necessary requirements
for locality. An anyon operator is obtained as the product $\varphi=\sigma\mu$.
A detailed and comprehensive study of the euclidean correlation functions of
$\sigma$, $\mu$ and $\varphi$ is carried on in the four theories above. The
exact correlation functions are obtained in cases $\underline{a}$ and
$\underline{c}$. The large distance behavior of them is obtained in cases
$\underline{b}$ and $\underline{d}$. The study of these correlation functions
allows one to draw conclusions about the condensation of charge and magnetic
flux, establishing thereby an analogy with the Ising model. The mass of vortex
and anyon excitations is explicitly obtained wherever these excitations are
present in the spectrum. The independence between the mechanisms of mass
generation for the vortices and for the vector field is clearly exposed.
|
hep-th/9208062
| 727,434 |
The formalism and applications of chiral perturbation theory for hadrons
containing a single heavy quark are discussed. We emphasize the utility of
working directly with the velocity dependent ``super'' fields which appear in
the chiral Lagrangian and whose interactions manifestly preserve heavy quark
spin symmetry rather than their individual spin components. Chiral logarithm
corrections to meson and baryon Isgur-Wise functions are found using these
fields.
We also identify a unique dimension-five operator which couples the axial
vector Goldstone current to the heavy antitriplet baryon field $T_\Q$. We then
compute the differential rate for the spin symmetry violating decay $T_b(v) \to
T_c(v') \ell \bar{\v}_\ell \pi$. The ratio of this decay rate to that for the
corresponding pure semileptonic transition can be studied away from the zero
recoil point.
|
hep-ph/9208244
| 727,434 |
The S-matrices for the scattering of two excitations in the XYZ model and in
all of its SU(n)-type generalizations are obtained from the asymptotic behavior
of Kerov's generalized Hall-Littlewood polynomials. These physical scattering
processes are all reduced to geometric s-wave scattering problems on certain
quantum-symmetric spaces, whose zonal spherical functions these
Hall-Littlewood-Kerov polynomials are. Mathematically, this involves a
generalization with an unlimited number of parameters of the Macdonald
polynomials. Physically, our results suggest that, of the (1+1)-dimensional
models, the integrable ones are those, for which the scattering of excitations
becomes geometric in the sense above.
|
hep-th/9208063
| 727,434 |
The action of Ashtekar gravity have been found by Cappovilla, Jacobson and
Dell. It does not depend on the metric nor the signature of the space-time. The
action has a similar structure as that of a massless relativistic particle. The
former is naturally generalized by adding a term analogous to a mass term of
the relativistic particle. The new action possesses a constant parameter
regarded as a kind of a cosmological constant. It is interesting to find a
covariant Einstein equation from the action. In order to do it we will examine
how the geometrical quantities are determined from the non-metric action and
how the Einstein equation follows from it.
|
gr-qc/9208010
| 727,435 |
Gravitational-wave interferometers are expected to monitor the last three
minutes of inspiral and final coalescence of neutron star and black hole
binaries at distances approaching cosmological, where the event rate may be
many per year. Because the binary's accumulated orbital phase can be measured
to a fractional accuracy $\ll 10^{-3}$ and relativistic effects are large, the
waveforms will be far more complex, carry more information, and be far harder
to model theoretically than has been expected. Theorists must begin now to lay
a foundation for extracting the waves' information.
|
astro-ph/9208005
| 727,435 |
The number $\langle N_s\rangle$ of solutions of the equations of Thouless,
Anderson and Palmer for p--spin interaction spin glass models is calculated.
Below a critical temperature $T_c$ this number becomes exponentially large, as
it is in the SK--model ($p=2$). But in contrast to this, for any $p>2$ the
factor $\alpha(T)=N^{-1} \ln\langle N_s\rangle$ jumps discontinuously at
$T_c(p)$, which is consistent with the discontinuity occuring within the
mean--field theory for these models. For zero temperature the results obtained
by Gross and M\'ezard are reproduced, and for $p\rightarrow\infty$ one gets the
result for the random energy model.
|
cond-mat/9208015
| 727,435 |
We investigate the stability of the electroweak Z-string at high
temperatures. Our results show that while finite temperature corrections can
improve the stability of the Z-string, their effect is not strong enough to
stabilize the Z-string in the standard electroweak model. Consequently, the
Z-string will be unstable even under the conditions present during the
electroweak phase transition. We then consider phenomenologically viable models
based on the gauge group $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ and show
that metastable strings exist and are stable to small perturbations for a large
region of the parameter space for these models. We also show that these strings
are superconducting with bosonic charge carriers. The string superconductivity
may be able to stabilize segments and loops against dynamical contraction.
Possible implications of these strings for cosmology are discussed.
|
hep-ph/9208245
| 727,435 |
Using a formalism developed by Polychronakos, we explicitly construct a set
of invariants of the motion for the Haldane-Shastry $SU(N)$ chain.
|
cond-mat/9208016
| 727,435 |
It is shown that quantum fluctuations due to a nontrivial gravitational
background in the flat radiation dominated universe can play an important
cosmological role generating nonvanishing cosmological global charge, e.g.
baryon number, asymmetry. The explicit form of the fluctuations at vacuum and
at finite temperature is given. Implications for particle physics are
discussed.
|
hep-ph/9208246
| 727,435 |
We construct a simple analytical model to study the effects of cosmic strings
on the microwave background radiation. Our model is based on counting random
multiple impulses inflicted on photon trajectories by the string network
between the time of recombination and today. We construct the temperature
auto-correlation function and use it to obtain the effective power spectrum
index n, the rms-quadrupole-normalized amplitude $Q_{rms-PS}$ and the rms
temperature variation smoothed on small angular scales. For the values of the
scaling solution parameters obtained in Refs.\cite{bb90},\cite{as90} we obtain
$n=1.14 \pm 0.5$, $Q_{rms-PS}=(4.5\pm 1.5) G\mu$ and $({{\Delta T}\over
T})_{rms}=5.5 G\mu$. Demanding consistency of these results with the COBE data
leads to $G\mu=(1.7 \pm 0.7)\times 10^{-6}$ (where $\mu$ is the string mass per
unit length), in good agreement with direct normalizations of $\mu$ from
observations.
|
hep-ph/9208247
| 727,435 |
We calculate the relic abundance of Higgsino-dominant lightest
superparticles, taking account of coannihilations with the superparticles which
are almost degenerate with the lightest one. We show that their relic abundance
is reduced drastically by the coannihilation processes and hence they are
cosmologically of no interest.
|
hep-ph/9208251
| 727,436 |
Simulations of vortex tube dynamics reveal that the non-Gaussian nature of
turbulent fluctuation originates in the effect of random advection. A similar
non-Gaussian distribution is found numerically in a simplified statistical
model of random advection. An analytical solution is obtained in the mean-field
case.
|
cond-mat/9208017
| 727,436 |
In the large $N_c$ limit, the $\Lambda_b$ and $\Lambda_c$ can be treated as
bound states of chiral solitons and mesons containing a heavy quark. We show
that the soliton and heavy meson are bound in an attractive harmonic oscillator
potential. The Isgur-Wise function for $\Lambda_b\rightarrow\Lambda_c\,
e^-\,\bar\nu_e$ decay is computed in the large $N_c$ limit. Corrections to the
form factor which depend on $m_N/ m_Q$ can be summed exactly ($m_N$ and $m_Q$
are the nucleon and heavy quark masses). We find that this symmetry breaking
correction at zero recoil is only $1\%$.
|
hep-ph/9208248
| 727,436 |
Fully developed turbulence is analised with the lattice model employing
vortex tube representation which is introduced recently by the authors. Several
characteric features observed in experiments and direct numeric integrations
are reproduced. Not only Kolmogorov's inertial range is observed, but also
several local probability distribution functions are obtained as well. Those of
the local velocities are close to the Gaussian and exponential-like
distributions appear in local vorticity, relative velocities and local velocity
consisting of only higher wave number components. Coherent structure of vortex
tubes is seen, too. Moreover required cpu-time and memory-size are very little
comparing with the conventional pseudo-spectral method. keywords : fluid
turbulence, vortex tube, lattice model, numerical technic.
|
cond-mat/9208018
| 727,436 |
Possible dimerization patterns and electronic structures in fullerene tubules
as the \pi-conjugated systems are studied with the extended Su-Schrieffer-
Heeger model. We assume various lattice geometries, including helical and
nonhelical tubules, and tubules with end caps. The model is solved for the
half-filling case of \pi-electrons. (1) When the undimerized systems do not
have a gap, the Kekul\'{e} structures tend to occur. These structures are
commensurate with the boundary condition in the direction perpendicular to the
tubular axis. The energy gap is of the order of the room temperatures at most.
Thus, the nearly metallic properties would be expected. (2) If the undimerized
systems have a large gap (\sim 1eV), the most stable structures are the
chain-like distortions where the direction of the arranged {\sl
trans}-polyacetylene chains is along almost the tubular axis. When we try to
obtain the Kekul\'{e} structures, the mismatch of the boundary condition occurs
and they are energetically unfavorable. The electronic structures are of
semiconductors due to the large gap.
|
cond-mat/9208019
| 727,436 |
In this article, I discuss W.Kohn's criterion for a metal insulator
transition, within the framework of a one band Hubbard model. This and related
ideas are applied to 1-dimensional Hubbard systems, and some intersting
miscellaneous results discussed. The Jordan Wigner transformation converting
the two species of fermions to two species of hardcore bosons is performed in
detail, and the ``extra phases'' arising from odd-even effects are explicitly
derived. Bosons are shown to prefer zero flux (i.e. diamagnetism), and the
corresponding ``happy fluxes'' for the fermions identified. A curious result
following from the interplay between orbital diamagnetism and spin polarization
is highlighted.
A ``spin-statistics'' like theorem, showing that the anticommutation
relations between fermions of opposite spin are crucial to obtain the SU(2)
invariance is pointed out.
|
cond-mat/9208021
| 727,436 |
We examine the spin-dependence of standard model Higgs boson production at
large transverse momentum via the processes $gg \rightarrow gH^0$, $qg
\rightarrow qH^0$, and $q\overline{q} \rightarrow gH^0$. The partonic level
spin-spin asymmetries ($\hat{a}_{LL}$) for these processes are large at SSC/LHC
energies.
|
hep-ph/9208250
| 727,436 |
Results from the study of hadronic jets in hadron-hadron collisions at order
$\alpha_s^3$ in perturbation theory are presented. The focus is on various
features of the internal structure of jets. The numerical results of the
calculation are compared with data where possible and exhibit reasonable
agreement.
|
hep-ph/9208249
| 727,436 |
This paper is relevant to the recent optical transmission experiments of
Karrai et al. for vortices in high Tc superconductors. We begin with a
substantial review and introduction. The microscopic response of vortices is
calculated from the Bogoliubov-deGennes equation, including an equation of
motion and conductivity. We find that the expected resonant dipole transtition
is not present because of translation invariance. We consider the effect of
pinning and show that in the presence of pinning one recovers the dipole
resonance. Thus we conclude that pinning may play an important role in the
experiment.
|
cond-mat/9208020
| 727,436 |
Nonminimal substitution terms in electroweak currents are studied in
effective chiral soliton models. It is found that the terms describing the
structure of the pion lead to sizable effects in form factors and
polarizabilities of the nucleon.
|
hep-ph/9208252
| 727,436 |
Hedgehog model predictions for the leading nonanalytic behavior (in
$m^{2}_{\pi }$) of certain observables are shown to agree with the predictions
of chiral perturbation theory up to an overall factor which depends on the
operator. This factor can be understood in terms of contributions of the
$\Delta$ isobar in chiral loops. These physically motivated contributions are
analyzed in an expansion in which both $m_{\pi}$ and $M_{\Delta}-M_N$ are taken
as small parameters, and are shown to yield large corrections to both hedgehog
models and chiral perturbation theory.
|
hep-ph/9208253
| 727,436 |
We show directly in the Lax operator approach how the Virasoro and
W-constraints on the $\tau$-function arise in the $p$-reduced KP hierarchy or
generalized KdV hierarchy. In partiacular, we consider the KdV and Boussinesq
hierarchy to show that the Virasoro and W-constraints follow from the string
equation by expanding the ``additional symmetry" operator in terms of the Lax
operator. We also mention how this method could be generalized for higher KdV
hierarchies.
|
hep-th/9208065
| 727,436 |
We calculate the decay rates of $B$ mesons into P-wave charmonium states
using new factorization formulas that are valid to leading order in the
relative velocity of the charmed quark and antiquark and to all orders in the
running coupling constant of QCD. We express the production rates for all four
P states in terms of two nonperturbative parameters, the derivative of the
wavefunction at the origin and another parameter related to the probability for
a charmed-quark-antiquark pair in a color-octet S-wave state to radiate a soft
gluon and form a P-wave bound state. Using existing data on $B$ meson decays
into $\chi_{c1}$ to estimate the color-octet parameter, we find that the
color-octet mechanism may account for a significant fraction of the $\chi_{c1}$
production rate and that $B$ mesons should decay into $\chi_{c2}$ at a similar
rate.
|
hep-ph/9208254
| 727,436 |
The electromagnetic properties of the SU(3)-flavor baryon decuplet are
examined within a lattice simulation of quenched QCD. Electric charge radii,
magnetic moments, and magnetic radii are extracted from the E0 and M1 form
factors. Preliminary results for the E2 and M3 moments are presented giving the
first model independent insight to the shape of the quark distribution in the
baryon ground state. As in our octet baryon analysis, the lattice results give
evidence of spin-dependent forces and mass effects in the electromagnetic
properties. The quark charge distribution radii indicate these effects act in
opposing directions. Some baryon dependence of the effective quark magnetic
moments is seen. However, this dependence in decuplet baryons is more subtle
than that for octet baryons. Of particular interest are the lattice predictions
for the magnetic moments of $\Omega^-$ and $\Delta^{++}$ for which new recent
experimental measurements are available. The lattice prediction of the
$\Delta^{++}/p$ ratio appears larger than the experimental ratio, while the
lattice prediction for the $\Omega^-/p$ magnetic moment ratio is in good
agreement with the experimental ratio.
|
hep-lat/9208025
| 727,436 |
We study the higher spin anologs of the six vertex model on the basis of its
symmetry under the quantum affine algebra $U_q(\slth)$. Using the method
developed recently for the XXZ spin chain, we formulate the space of states,
transfer matrix, vacuum, creation/annihilation operators of particles, and
local operators, purely in the language of representation theory. We find that,
regardless of the level of the representation involved, the particles have spin
$1/2$, and that the $n$-particle space has an RSOS-type structure rather than a
simple tensor product of the $1$-particle space. This agrees with the picture
proposed earlier by Reshetikhin.
|
hep-th/9208066
| 727,437 |
The restricted solid-on-solid models in the anti-ferromagnetic regime is
studied in the framework of quantum affine algebras. Following the line
developed recently for vertex models, a representation theoretical picture is
presented for the structure of the space of states. The local operators and the
creation/annihilation operators of quasi-particles are defined using vertex
operators, and their commutation relations are calculated.
|
hep-th/9208067
| 727,437 |
We show that under certain astrophysical conditions a binary system
consisting of two compact objects can be stabilized against indefinite
shrinking of orbits due to the emission of gravitational radiation. In this
case, the lighter binary companion settles down to a stable orbit when the loss
of the angular momentum due to gravitational radiation becomes equal to its
gain from the accreting matter from the disk around the more massive primary.
We claim that such systems can be stable against small perturbations and can be
regarded as steady emitters of gravitational waves of constant frequency and
amplitude. Furthermore, X-rays emitted by the secondary can also produce
astrophysically interesting situations when coupled with gravitational lensing
and Doppler effects.
|
astro-ph/9208006
| 727,437 |
We investigate extensions of the N=2 super Virasoro algebra by one additional
super primary field and its charge conjugate. Using a supersymmetric covariant
formalism we construct all N=2 super W-algebras up to spin 5/2 of the
additional generator. Led by these first examples we close with some
conjectures on the classification of N=2 ${\cal SW}(1,\Dt)$ algebras.
|
hep-th/9208069
| 727,437 |
In this contribution to the proceedings we will describe some of the details
for constructing the Gribov horizon and the boundary of the fundamental modular
domain, when restricting to some low energy modes of pure SU(2) gauge theory in
a spherical spatial geometry. The fundamental domain is a one-to-one
representation of the set of gauge invariant degrees of freedom, in terms of
transverse gauge fields. Boundary identifications are the only remnants of the
Gribov copies.
|
hep-lat/9208027
| 727,437 |
We present new results on the static qq-potential from high statistics
simulations on 32^4 and smaller lattices, using the standard Wilson beta = 6.0,
6.4, and 6.8. Within our statistical errors we do not observe any finite size
effects affecting the potential values, on varying the spatial lattice extent
from 0.9fm up to 3.3fm. We are able to see and quantify the running of the
coupling from the Coulomb behaviour of the interquark force. From this we
extract the ratio \sqrt{sigma}/Lambda_L. We demonstrate that scaling violations
on the string tension can be considerably reduced by introducing effective
coupling schemes, which allow for a safe extrapolation of \Lambda_L to its
continuum value. Both methods yield consistent values for Lambda: Lambda_MSbar
= 0.558_{-0.007}^{+0.017}\sqrt{sigma} = 246_{-3}^{+7}MeV. At the highest energy
scale attainable to us we find alpha(5 GeV) = 0.150(3)
|
hep-lat/9208028
| 727,437 |
There is a growing interest in the possibility that dark matter could be
formed of weakly interacting particles with a mass in the 100 GeV - 2 TeV
range, and supersymmetric particles are favorite candidates. If they constitute
the dark halo of our Galaxy, their mutual annihilations produce energetic gamma
rays that could be detected using existing atmospheric \u{C}erenkov techniques.
|
hep-ph/9208255
| 727,437 |
We study $D$-dimensional polymerized membranes embedded in $d$ dimensions
using a self-consistent screening approximation. It is exact for large $d$ to
order $1/d$, for any $d$ to order $\epsilon=4-D$ and for $d=D$. For flat
physical membranes ($D=2,d=3$) it predicts a roughness exponent $\zeta=0.590$.
For phantom membranes at the crumpling transition the size exponent is
$\nu=0.732$. It yields identical lower critical dimension for the flat phase
and crumpling transition $D_{lc}(d)={2 d \over {d+1}}$ ($D_{lc}={\sqrt{2}}$ for
codimension 1). For physical membranes with ${\it random}$ quenched curvature
$\zeta=0.775$ in the new $T=0$ flat phase in good agreement with simulations.
|
cond-mat/9208023
| 727,437 |
The structural and electronic properties of cubic GaN are studied within the
local density approximation by the full-potential linear muffin-tin orbitals
method. The Ga $3d$ electrons are treated as band states, and no shape
approximation is made to the potential and charge density. The influence of $d$
electrons on the band structure, charge density, and bonding properties is
analyzed. It is found that due to the energy resonance of the Ga 3$d$ states
with nitrogen 2$s$ states, the cation $d$ bands are not inert, and features
unusual for a III-V compound are found in the lower part of the valence band
and in the valence charge density and density of states. To clarify the
influence of the Ga $d$ states on the cohesive properties, additional full and
frozen--overlapped-core calculations were performed for GaN, cubic ZnS, GaAs,
and Si. The results show, in addition to the known importance of non-linear
core-valence exchange-correlation corrections, that an explicit description of
closed-shell repulsion effects is necessary to obtain accurate results for GaN
and similar systems. In summary, GaN appears to be somewhat exceptional among
the III-V compounds and reminiscent of II-VI materials, in that its band
structure and cohesive properties are sensitive to a proper treatment of the
cation $d$ bands, as a result of the presence of the latter in the valence band
range.
|
cond-mat/9208022
| 727,437 |
We extend the considerations of a previous paper on black hole statistical
mechanics to the case of black extended objects such as black strings and black
membranes in 10-dimensional space-time. We obtain a general expression for the
Euclidean action of quantum black p-branes and derive their corresponding
degeneracy of states. The statistical mechanics of a gas of black p-branes is
then analyzed in the microcanonical ensemble. As in the case of black holes,
the equilibrium state is not thermal and the stable configuration is the one
for which a single black object carries most of the energy. Again, neutral
black p-branes obey the bootstrap condition and it is then possible to argue
that their scattering amplitudes satisfy crossing symmetry. Finally, arguments
identifying quantum black p-branes with ordinary quantum branes of different
dimensionality are presented.
|
hep-th/9208070
| 727,437 |
We study numerically the SU(2) Kazakov-Migdal model of `induced QCD'. In
contrast to our earlier work on the subject we have chosen here {\it not} to
integrate out the gauge fields but to keep them in the Monte Carlo simulation.
This allows us to measure observables associated with the gauge fields and
thereby address the problem of the local $Z_2$ symmetry present in the model.
We confirm our previous result that the model has a line of first order phase
transitions terminating in a critical point. The adjoint plaquette has a clear
discontinuity across the phase transition, whereas the plaquette in the
fundamental representation is always zero in accordance with Elitzur's theorem.
The density of small $Z_2$ monopoles shows very little variation and is always
large. We also find that the model has extra local U(1) symmetries which do not
exist in the case of the standard adjoint theory. As a result, we are able to
show that two of the angles parameterizing the gauge field completely decouple
from the theory and the continuum limit defined around the critical point can
therefore not be `QCD'.
|
hep-lat/9208029
| 727,437 |
Electromagnetic polarizabilities of the nucleon are analyzed in a hedgehog
model with quark and meson degrees of freedom.
|
hep-ph/9208256
| 727,437 |
Linear response theory for SU(2) hedgehog soliton models is developed.
|
hep-ph/9208257
| 727,437 |
Affine transformations (dilatations and translations) are used to define a
deformation of one-dimensional $N=2$ supersymmetric quantum mechanics.
Resulting physical systems do not have conserved charges and degeneracies in
the spectra. Instead, superpartner Hamiltonians are $q$-isospectral, i.e. the
spectrum of one can be obtained from another (with possible exception of the
lowest level) by $q^2$-factor scaling. This construction allows easily to
rederive a special self-similar potential found by Shabat and to show that for
the latter a $q$-deformed harmonic oscillator algebra of Biedenharn and
Macfarlane serves as the spectrum generating algebra. A general class of
potentials related to the quantum conformal algebra $su_q(1,1)$ is described.
Further possibilities for $q$-deformation of known solvable potentials are
outlined.
Talk presented at the workshop on Harmonic Oscillators, College Park, 25-28
March 1992.
|
hep-th/9208073
| 727,437 |
We study superdifferential operators of order $2n+1$ which are covariant with
respect to superconformal changes of coordinates on a compact super Riemann
surface. We show that all such operators arise from super M\"obius covariant
ones. A canonical matrix representation is presented and applications to
classical super W algebras are discussed.
|
hep-th/9208072
| 727,437 |
We study non-linear sigma models with N local supersymmetries in three
space-time dimensions. For N=1 and 2 the target space of these models is
Riemannian or Kahler, respectively. All N>2 theories are associated with
Einstein spaces. For N=3 the target space is quaternionic, while for N=4 it
generally decomposes into two separate quaternionic spaces, associated with
inequivalent supermultiplets. For N=5,6,8 there is a unique (symmetric) space
for any given number of supermultiplets. Beyond that there are only theories
based on a single supermultiplet for N=9,10,12 and 16, associated with coset
spaces with the exceptional isometry groups $F_{4(-20)}$, $E_{6(-14)}$,
$E_{7(-5)}$ and $E_{16(+8)}$, respectively. For $N=3$ and $N\geq5$ the $D=2$
theories obtained by dimensional reduction are two-loop finite.
|
hep-th/9208074
| 727,438 |
The first exploratory calculations of QCD vacuum correlation functions on a
lattice are reported. Qualitative agreement with phenomenological results is
obtained in channels for which experimental data are available, and these
correlation functions are shown to be useful in exploring approximations based
on sum rules and interacting instantons.
|
hep-lat/9208030
| 727,438 |
Extended technicolor theories generate potentially large corrections to the
$\Zbb$ vertex. These can be observed in current experiments at LEP.
|
hep-ph/9208259
| 727,438 |
A consequence of non-Gaussian perturbations on the Sachs-Wolfe effect is
studied. For a particular power spectrum, predicted Sachs-Wolfe effects are
calculated for two cases: Gaussian (random phase) configuration, and a specific
kind of non-Gaussian configuration. We obtain a result that the Sachs-Wolfe
effect for the latter case is smaller when each temperature fluctuation is
properly normalized with respect to the corresponding mass fluctuation ${\delta
M\over M}(R)$. The physical explanation and the generality of the result are
discussed.
|
gr-qc/9208011
| 727,438 |
A large class of cosmological solutions (of the Einstein equations) in string
theory, in the presence of Maxwell fields, is obtained by $O(d,d)$
transformations of simple backgrounds with $d$ toroidal isometries. In all the
examples in which we find a (closed) expanding universe, such that the universe
admits a smooth, complete initial value hypersurface, a naked singularity may
form only at the time when the universe collapses. The discrete symmetry group
$O(d,d,Z)$ identifies different cosmological solutions with a background
corresponding to a (relatively) simple CFT, and therefore, may be useful in
understanding the properties of naked singularities in string theory.
|
hep-th/9208076
| 727,438 |
The magnetic field effects on lattice wavefunctions of Hofstadter electrons
strongly localized at boundaries are studied analytically and numerically. The
exponential decay of the wavefunction is modulated by a field dependent
amplitude J(t) which depends sensitively on the value of alpha (the magnetic
flux per plaquette in units of a flux quantum, t is the distance from the
boundary). While for rational values p/q, the envelope of J(t) increases as
2**t/q, the behavior for irrational alpha is erratic with an aperiodic
structure which changes drastically with alpha. For algebraic alpha it is found
that J(t) increases as a power law t**b(alpha) while it grows faster for
transcendental alpha. This is very different from the growth rate exp{sqrt(t)}
typical for random phases. The theoretical analysis is extended to lattices in
which the distances between adjacent layers increase as r**n with n>0.
Different behavior of J(t;n) is found in various regimes of n. It changes from
periodic for small n to random like for large n.
|
cond-mat/9208024
| 727,439 |
We study the interfacial adsorption phenomena of the three-state
ferromagnetic Potts model on the simple cubic lattice by the Monte Carlo
method. Finite-size scaling analyses of the net-adsorption yield the evidence
of the phase transition being of first-order and $k_{\rm B} T_{\rm C} / J =
1.8166 (2)$.
|
cond-mat/9208025
| 727,441 |
We present a generalization of the $U(1)^{2}$ charged dilaton black holes
family whose main feature is that both $U(1)$ fields have electric and magnetic
charges, the axion field still being trivial. We show the supersymmetry of
these solutions in the extreme case, in which the corresponding generalization
of the Bogomolnyi bound is saturated and a naked singularity is on the verge of
being visible to external observers. Then we study the action of a subset of
the $SL(2,R)$ group of electric-magnetic duality rotations that generates a
non-trivial axion field on those solutions. This group of transformations is an
exact symmetry of the $N=4$ $d=4$ ungauged supergravity equations of motion. It
has been argued recently that it could be an exact symmetry of the full
effective string theory. The generalization of the Bogomolnyi bound is
invariant under the full $SL(2,R)$ and the solutions explicitly rotated are
shown to be supersymmetric if the originals are. We conjecture that any
$SL(2,R)$ transformation will preserve supersymmetry.
|
hep-th/9208078
| 727,441 |
In the minimal Standard Model (MSM) with three generations of quarks and
leptons, neutrinos can have tiny charges consistent with electromagnetic gauge
invariance. There are three types of non-standard electric charge, given by
$Q_{st} + \epsilon(L_i - L_j)$, where $i, j = e, \mu, \tau$ $(i \neq j)$,
$Q_{st}$ is standard electric charge, $L_i$ is a family-lepton--number, and
$\epsilon$ is an arbitrary parameter which is put equal to zero in the usual
incarnation of the MSM. These three non-standard electric charges are of
considerable theoretical interest because they are compatible with the MSM
Lagrangian and $SU(3)_c \otimes SU(2)_L \otimes U(1)_Y$ gauge anomaly
cancellation. The two most conspicuous implications of such non-standard
electric charges are the presence of two generations of massless charged
neutrinos and a breakdown in electromagnetic universality for $e$, $\mu$ and
$\tau$. We use results from (i) charge conservation in $\beta$-decay, (ii)
physical consequences of charged atoms in various contexts, (iii) the anomalous
magnetic moments of charged leptons, (iv) neutrino-electron scattering, (v)
energy loss in red giant and white dwarf stars, and (vi) limits on a
cosmologically induced thermal photon mass, to place bounds on $\epsilon$.
While the constraints derived for $\epsilon$ 10^{-21}$), the $L_{\mu}-L_{\tau}$
case allows $\epsilon$ to be as large as $10^{-14}$.
|
hep-ph/9208260
| 727,441 |
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