November 1993 arXiv papers — page 4

J. Baumgartner, A. Hajnal. S. Todorcevic

We establish a variety of extensions to the Erdos-Rado Theorem, particularly involving ordinal numbers, and always involving ordinary partition relations. Most of the results can be regarded as consequences of the Ramification Principle, interpreted appropriately. Some of these problems have been open for a long time. There is a detailed summary at the begin

I. Ya. Aref'eva

We study the Regge regime of QCD as a special regime of lattice gauge theory on an asymmetric lattice. This lattice has a spacing $a_0 $ in the longitudinal direction and a spacing $a_t $ in the transversal direction. The limit $\frac{a_{0}}{a_{t}} \to 0$ corresponds to correlation functions with small longitudinal and large transversal coordinates, i.e. lar

T. Heinzl, E. Werner

In the light front quantisation scheme initial conditions are usually provided on a single lightlike hyperplane. This, however, is insufficient to yield a unique solution of the field equations. We investigate under which additional conditions the problem of solving the field equations becomes well posed. The consequences for quantisation are studied within

Shau-Jin Chang, R. Rajaraman

We study chiral vertex operators in the sine-Gordon [SG] theory, viewed as an off-conformal system. We find that these operators, which would have been primary fields in the conformal limit, have interesting and, in some ways, unexpected properties in the SG model. Some of them continue to have scale- invariant dynamics even in the presence of the non-confor

S. C. S. Silva, P. C. R. C. Mello, M. C. Nemes

In the present contribution we show that the introduction of a conserved axial current in electrodynamics can explain the quantization of electric charge, preserving parity conservation, and introduces a dynamical discreteness into space-time.

J. Gonzalez, F. Guinea, M. A. H. Vozmediano

A system of electrons in the two-dimensional honeycomb lattice with Coulomb interactions is described by a renormalizable quantum field theory similar but not equal to QED_3. Renormalization group techniques are used to investigate the infrared behaviour of the system that flows to a fixed point with non-Fermi liquid characteristics. There are anomalous dime

J. -B. Zuber

After a short review of the algebraic setting of N=2 superconformal field theories, their chiral ring and their perturbations, I present some recent results on curious relations between the integrability of their perturbations and algebraic properties of their deformed chiral ring. (Lecture given at Hang-zhou, China, Sept 1993)

Alberto Sirlin

The evidence for electroweak radiative corrections not contained in $α(m_Z)$ is examined. At low energies there is very strong evidence in the analysis of the unitarity of the CKM matrix. At LEP and collider experiments the current direct signals are not strong, but there is substantial indirect evidence, which will likely become sharper when $m_t$ is determ

Alon E. Faraggi

I discuss the correspondence between realistic four dimensional free fermionic models and $Z_2\times Z_2$ orbifold compactification. %I illustrate this correspondence for one particular example. I discuss the properties of the $Z_2\times Z_2$ orbifold that are reflected in the realistic free fermionic models. I argue that the properties of the realistic free

L. McLerran

I discuss the problem of computing the structure functions for very heavy nuclei at small Bjorken x. The approximations used in this description are physically motivated, and recent computations reviewed.

Stefano Ranfone

In the context of the supersymmetric flipped $SU(5)\otimes U(1)$ GUT model, we have studied in detail the neutrino mass spectrum, obtaining an approximate formula for the corresponding effective three-generation mass matrix. It is found that at least two neutrinos are expected to have extremely small masses of no particular interest. The third neutrino, on t

Michael Luke, Martin J. Savage, Mark B. Wise

We compute the differential momentum correlation function for hadrons produced in the decay of $B$-mesons. This measure of hadronic event shapes tests the free $b$-quark decay picture for nonleptonic and semileptonic decays of $B$-mesons. Our results can also be applied to $B_s$ and $Λ_b$ decay.

A. Kusenko, R. Shrock

We construct new invariants and give several theorems which determine in general (i) the number of physically meaningful phases in charged lepton and neutrino mass matrices and (ii) which elements of these matrices can be rendered real by rephasings. We illustrate our results with simple models.

K. M. Bitar, P. Vranas

The main results of our analysis of the two flavor Nambu--Jona-Lasinio model with $SU(2) \times SU(2)$ chiral symmetry on the four--dimensional hypercubic lattice with naive and Wilson fermions are presented. Large $N$ techniques and numerical simulations are used to study various properties of the model. The scalar and pseudoscalar spectrum, the approach to

Martin Grabenstein, Bernhard Mikeska

We pose two questions about the dynamical critical behavior of multigrid Monte Carlo: Will a multigrid Monte Carlo simulation of the two dimensional Sine Gordon model exhibit critical slowing down, as expected by a theoretical analysis of Metropolis acceptance rates? Can we reduce critical slowing down caused by decreasing acceptance rates on large blocks by

R. Altmeyer, M. Goeckeler, R. Horsley, E. Laermann

A lattice calculation of the pi-N sigma term is described using dynamical staggered fermions. Preliminary results give a sea term comparable in magnitude to the valence term.

A. Patrascioiu, E. Seiler

In dimension $D\leq 2$ the low temperature behavior of systems enjoying a continuous symmetry is dominated by super-instantons: classical configurations of arbitrarily low energy. Perturbation theory in the background of a super-instanton produces thermodynamic answers for the invariant Green's functions that differ from the standard ones, but only in no

E. Brézin, École Normale Superieure, A. Zee

We study the correlation between the energy spectra of two disordered Hamiltonians of the form $H_a=H_{0a}+s_{a}φ$ ($a=1,2$) with $H_{0a}$ and $φ$ drawn from random distributions. We calculate this correlation function explicitly and show that it has a simple universal form for a broad class of random distributions.

A. V. Chubukov, T. Senthil, S. Sachdev

We present a theory of frustrated, two-dimensional, quantum antiferromagnets in the vicinity of a quantum transition from a non-collinear, magnetically-ordered ground state to a quantum-disordered phase. Using a sigma-model for bosonic, spin-1/2, spinon fields, we obtain universal scaling forms for a variety of observables. Our results are compared with nume

J. Gonzalez, F. Guinea, M. A. H. Vozmediano

We study the Coulomb interactions in fullerene molecules within a continuum formalism. The model gives rise to a renormalizable field theory, which has many similarities to standard quantum electrodynamics. The effective electric charge at low energies is reduced by screening processes. The associated renormalization of the one electron Green's function

A. Kashlinsky

We review how the various large-scale data constrain cosmological parameters and, consequently, theories for the origin of large-scale structure in the Universe. We discuss the form of the power spectrum implied by the correlation data of galaxies and argue by comparing the velocity field implied by the distribution of light with the observed velocity flows

R. J. Nemiroff, J. P. Norris, C. Kouveliotou, G. J. Fishman

A simple test for time-asymmetry is devised and carried out on the brightest gamma-ray bursts detected by the Burst and Transient Source Experiment (BATSE) on board the {\it Compton} Gamma Ray Observatory. We show evidence that individual bursts are time-asymmetric on all time scales tested, from a time scale shorter than that of pulses which compose GRBs to

D. E. Di Gregorio, A. Gattone, H. Huck, A. O. Macchiavelli

Contains a summary, current status and prospects for the direct detection of cold dark matter using diurnal modulation effects as presented at the ELAF 93, Mar del Plata Argentina. The potential advantages of using the Earth as an absorber to produce diurnal modulation effects in cold dark matter searches are given along with some estimates of counting rates

Biman B. Nath, Peter L. Biermann

We consider a cosmic ray spectrum that is a power law in momentum down to a cutoff and derive a lower cutoff corresponding to $E_{kin} \sim (30-60)$ MeV from the observed ionization rates in nearby diffuse clouds. While the real spectra of cosmic rays may not be so simple, we argue that one expects a substantial change in the spectra at such energies and tha

D. Pfenniger, F. Combes

Gas cloud models taking into account the recently disclosed fractal structure of cold gas are set up, showing that large errors in the classical gas mass determination based on smooth cloud models can easily follow if the gas is in reality fractal. Fractal clouds must present both optically thin and optically thick clumps in any single wavelength observation

D. Pfenniger, F. Combes, L. Martinet

Based on dynamical constraints about the Hubble sequence evolution, observational data and a number of "conspiracies", we propose that the dark matter around spiral galaxies is in the form of cold gas, essentially in molecular form and rotationally supported. (full A&A paper (in press) available by anonymous ftp at obssd8.unige.ch in /pub/fractal as

P. I. Krastev, S. T. Petcov

Two-neutrino oscillations in vacuum are studied as a possible solution of the solar neutrino problem. New constraints on the parameter sn2, characterizing the mixing of the electron neutrino with another active or sterile neutrino, as well as on the mass--squared difference, dm2, of their massive neutrino components, are derived using the latest results from

Peter Cho, Sandip P. Trivedi

Goldstone boson decays of P-wave $D_s^{**}$ mesons are studied within the framework of Heavy Hadron Chiral Perturbation Theory. We first analyze the simplest single kaon decays of these strange charmed mesons. We derive a model independent prediction for the width of $D_{s2}$ and use experimental information on $D_{s1}$ to constrain the S-wave contribution t

Volodymyr Lyubashenko, A. Sudbery

We introduce and study the Koszul complex for a Hecke $R$-matrix. Its cohomologies, called the Berezinian, are used to define quantum superdeterminant for a Hecke $R$-matrix. Their behaviour with respect to Hecke sum of $R$-matrices is studied. Given a Hecke $R$-matrix in $n$-dimensional vector space, we construct a Hecke $R$-matrix in $2n$-dimensional vecto

G. E. Arutyunov, P. B. Medvedev

We show that the external algebra $\cal M$ on $GL(N)$ can be equipped with the graded Poisson brackets compatible with the group action. We prove that there are only two graded Poisson-Lie structures (brackets) on $\cal M$ and we obtain their explicit description. We realize that just these two structures appear as the quasiclassical limit of the bicovariant

Claudio Emmrich, Alan Weinstein

B. Fedosov has given a simple and very natural construction of a deformation quantization for any symplectic manifold, using a flat connection on the bundle of formal Weyl algebras associated to the tangent bundle of a symplectic manifold. The connection is obtained by affinizing, nonlinearizing, and iteratively flattening a given torsion free symplectic con

C. Ciofi degli Atti, S. Scopetta, E. Pace, G. Salmè

A comprehensive treatement of the theoretical approach for describing nuclear effects in inclusive scattering of polarized electrons by polarized $^3$He is presented.

Arieh Iserles

The main difference between certain spectral problems for linear Schrödinger operators, e.g. the almost Mathieu equation, and three-term recurrence relations for orthogonal polynomials is that in the former the index ranges across $\ZZ$ and in the latter only across $\Zp$. We present a technique that, by a mixture of Dirichlet and Taylor expansions, translat

Stephen J. Dilworth, Alexander Koldobsky

We present a formula for the Fourier transforms of order statistics in $\Bbb R^n$ showing that all these Fourier transforms are equal up to a constant multiple outside the coordinate planes in $\Bbb R^n.$ For $a_1\geq ... \geq a_n\ge0$ and $q>0,$ denote by $\ell_{w,q}^n$ the $n$-dimensional Lorentz space with the norm $\|(x_1,...,x_n)\| = (a_1 (x_1^{*})^q +.

Anuradha Misra

Light front field theories are known to have the usual infra-red divergences of the equal time theories, as wellas new `spurious' infra-red divergences. The formar kind of IR divergences are usually treated by giving a small mass to the gauge particle. An alternative method to deal with these divergences is to calculate the transition matrix elements in

Ki-Myeong Lee

We introduce selfdual Maxwell-Higgs systems with uniform background electric charge density and show that the selfdual equations satisfied by topological vortices can be reduced to the original Bogomol'nyi equations without any background. These vortices are shown to carry no spin but to feel the Magnus force due to the shielding charge carried by the Hi

K. Scharnhorst

The Letter reconsiders a result obtained by Chrétien and Peierls in 1954 within nonlocal QED in 4D [Proc. Roy. Soc. London A 223, 468]. Starting from secondly quantized fermions subject to a nonlocal action with the kernel $[ i\not\partial_x a(x) - m b(x)]$ and gauge covariantly coupled to an external U(1) gauge field they found that for $a = b$ the induced

G. W. Gibbons, Alan R. Steif

Cosmological solutions with a homogeneous Yang-Mills field which oscillates and passes between topologically distinct vacua are discussed. These solutions are used to model the collapsing Bartnik-McKinnon gravitational sphaleron and the associated anomalous production of fermions. The Dirac equation is analyzed in these backgrounds. It is shown explicitly th

C. M. Becchi, R. Collina, C. Imbimbo

We provide a simple lagrangian interpretation of the meaning of the $b_0^-$ semi-relative condition in closed string theory. Namely, we show how the semi-relative condition is equivalent to the requirement that physical operators be cohomology classes of the BRS operators acting on the space of local fields {\it covariant} under world-sheet reparametrization

Konstadinos Sfetsos

We formulate WZW models based on a centrally extended version of the Euclidean group in $d$-dimensions. We obtain string backgrounds corresponding to conformal $\s$-models in $D=d^2$ space-time dimensions with exact central charge $c=d^2$ and $d(d-1)/2$ null Killing vectors. By identifying the corresponding conformal field theory we show that the one loop re

Curtis G. Callan, Igor R. Klebanov

We present a solution of the problem of a free massless scalar field on the half line interacting through a periodic potential on the boundary. For a critical value of the period, this system is a conformal field theory with a non-trivial and explicitly calculable S-matrix for scattering from the boundary. Unlike all other exactly solvable conformal field th

Chihong Chou

In this letter, we discuss the extension of Feynman's derivation of the equation of motion to the case of spinning particles. We show that a spinning particle interacts only with the electromagnetic and gravitational fields. In the absence of the electromagnetic interactions, we rederive Papapetrou's equations for spinning particles in the background

John Dixon

The supersymmetric standard model (SSM) contains a wealth of potential supersymmetry anomalies, all of which occur in the renormalization of composite operators of the theory. The coefficients of the weak-E.M. superanomalies should be related to the Witten indices of the neutrino and photon superfields, and the coefficients of the strong superanomalies shoul

A. Ballestrero, E. Maina

Heavy quark production in five jet events at $e^+e^-$ colliders is studied at tree level using helicity amplitudes. Total production rates for $2b3j$ and $4bj$ are given and compared with the corresponding results for massless quarks. The process $e^+e^-\rightarrow q\bar q ggγ$ which is the dominant contribution to $4jγ$ production is briefly discussed.

Yue Shen

We study a $U(N)\times U(N)$ symmetric scalar field model in four and three dimensions. First, using our data in four dimensions in the weak coupling region, we demonstrate explicitly that the observed first order phase transition is induced by quantum fluctuations. Next, based on the renormalization group and our new simulation results in three dimensions w

Stephen P. Braham

The Kuchař canonical transformation for vacuum geometrodynamics in the presence of cylindrical symmetry is applied to a general non-vacuum case. The resulting constraints are highly non-linear and non-local in the momenta conjugate to the Kuchař embedding variables. However, it is demonstrated that the constraints can be solved for these momenta and thus the

J. E. Nelson, T. Regge

In [1,2] we established and discussed the algebra of observables for $2+1$ gravity at both the classical and quantum level, and gave a systematic discussion of the reduction of the expected number of independent observables to $6g - 6 (g > 1)$. In this paper the algebra of observables for the case $g=2$ is reduced to a very simple form. A Hilbert space of st

M. R. Norman

In a recent Letter, Shen et al have detected a large anisotropy of the superconducting gap in Bi2212, consistent with d-wave symmetry, from photoemission spectroscopy. Moreover, they claim that the change in their spectra as a function of aging is also consistent with such an intrepretation. In this Comment, I show that the latter statement is not entirely c

Matthew P. A. Fisher

Transport through a tunnel junction connecting a superconductor to a spin-aligned quantum Hall fluid at filling $ν$ is studied theoretically. The dominant transport channel at low temperatures is the tunnelling of Cooper pairs into edge states of the quantum Hall fluid. This process, which is greatly suppressed at low energies due to both Coulomb and Pauli e

D. F. Wang, C. Gruber

In this work, we have studied the invariants of motion of two SU(N) supersymmetric t-J model of $1/r^2$ hopping and exchange in one dimension. The first model is defined on a lattice of equal spaced sites, and the second on a non-equal spacing lattice. Using the ``exchange operator formalism'', we are able to construct all the invariants for the mode

August E. Evrard

The abundance and internal characteristics of rich clusters of galaxies can provide useful constraints on models of large--scale structure formation. This article will review some recent three dimensional, multi--fluid simulations of cluster dynamics and discuss their impact on issues raised from optical and X-ray observations of clusters. In `bottom--up&#39

Ruth Durrer

After an introduction to the problem of cosmological structure formation, we develop gauge invariant cosmological perturbation theory. We derive the first order perturbation equations of Einstein's equations and energy momentum ``conservation''. Furthermore, the perturbations of Liouville's equation for collisionless particles and Boltzmann&#

R. Durrer, A. Howard, Z. -H. Zhou

The cosmic microwave anisotropies in a scenario of large scale structure formation with cold dark matter and texture are discussed and compared with recent observational results of the COBE satellite. A couple of important statistical parameters are determined. The fluctuations are slightly non gaussian. The quadrupole anisotropy is $1.5\pm 1.2\times 10^{-5}

Ruth Durrer

The cosmic microwave background (CMB) anisotropies have turned out to represent one of the most stringent 'bottle necks' for scenarios of large scale structure formation. As a possibility to relax this constraint, it has been proposed that early reionization can damp CMB fluctuations on small scales due to photon diffusion in the ionized plasma. As a

Ph. Blanchard, A. Jadczyk

Model interactions between classical and quantum systems are briefly reviewed. These include: general measurement - like couplings, Stern-Gerlach experiment, model of a counter, quantum Zeno effect, piecewise deterministic Markov processes and meaning of the wave function.

L. Bonora, C. S. Xiong

We show how to calculate correlation functions of two matrix models. Our method consists in making full use of the integrable hierarchies and their reductions, which were shown in previous papers to naturally appear in multi--matrix models. The second ingredient we use are the $W$--constraints. In fact an explicit solution of the relevant hierarchy, satisfyi

Xiao-Gang Wen, Yong-Shi Wu, Yasuhiro Hatsugai

In this paper we study the spectrum of low-energy edge excitations of a fractional quantum Hall (FQH) droplet. We show how to generate, by conformal field theory (CFT) techniques, the many-electron wave functions for the edge states. And we propose to classify the spectrum of the edge states by the same chiral operator product algebra (OPA) that appears in t

A. Wirzba, M. Kirchbach, D. O. Riska

We determine the $N_c$--dependence of the resonance contributions to the Adler--Weisberger sum rule for the inverse square $1/g_A^2$ of the axial charge coupling constant and show that in the large $N_c$ limit the contributions of the Roper-like excitations scale as $O(1/N_c)$. Consistency with the $1/N_c^2$ scaling of the $1/g_A^2$ term in the sum rule requ

D. V. Boulatov

I argue that the complete partition function of 3D quantum gravity is given by a path integral over gauge-inequivalent manifolds times the Chern-Simons partition function. In a discrete version, it gives a sum over simplicial complexes weighted with the Turaev-Viro invariant. Then, I discuss how this invariant can be included in the general framework of latt

E. Elizalde, S. D. Odintsov

A method for finding the renormalization group (RG) improved effective Lagrangian for a massive interacting field theory in curved spacetime is presented. As a particular example, the $λφ^4$-theory is considered and the RG improved effective Lagrangian is explicitly found up to second order in the curvature tensors. As a further application, the curvature-in

J. Alfaro

We derive the loop equations for the d-dimensional n-Hermitian matrix model. These are a consequence of the Schwinger-Dyson equations of the model. Moreover we show that in leading order of large $N$ the loop equations form a closed set. In particular we derive the loop equations for the $n=2^k$ matrix model recently proposed to describe the coupling of Two-

A. L. Larsen

We investigate the connection between curved spacetime and the emergence of string-instabilities, following the approach developed by Loustó and Sánchez for de Sitter and black hole spacetimes. We analyse the linearised equations determining the comoving physical (transverse) perturbations on circular strings embedded in Schwarzschild, Reissner-Nordström and

H. Lu, C. N. Pope, X. J. Wang, S. C. Zhao

Nilpotent BRST operators for higher-spin $W_{2,s}$ strings, with currents of spins 2 and $s$, have recently been constructed for $s=4$, 5 and 6. In the case of $W_{2,4}$, this operator can be understood as being the BRST operator for the critical $W\!B_2$ string. In this paper, we construct a generalised BRST operator that can be associated with a non-critic

Frank Wilczek

I have been asked to discuss the status of QCD. It seems to me that there are three main points to be made about the present status of QCD: $\bullet$ QCD is right, and we can do many beautiful things with it. $\bullet$ There are several important concrete problems that lie just beyond the edge of our current understanding. $\bullet$ There are some foundation

S. Hegyi

The relation of combinants to various statistics characterizing the fluctuation pattern of multihadron final states is discussed. Scaling laws are derived for count probabilities and combinants in the presence of homogeneous and clustered monofractal density fluctuations. It is argued that both types of scaling rules are well suited to signal Quark-Gluon Pla

Edi Halyo

We examine the light quark masses in a standard--like superstring model in the four dimensional free fermionic formulation. We find that the supersymmetry constraints in the observable and hidden sectors eliminate all large contributions to $m_u$ and $m_d$ and force them to be much smaller than the other quark masses. The requirement for an acceptable Higgs

Naoyuki Haba, Chuichiro Hattori, Masahisa Matsuda, Takeo Matsuoka

In Calabi-Yau superstring models it is found that two large intermediate energy scales of symmetry breaking can be induced for special types of the nonrenormalizable interactions. In the models one set of $SO(10)$-singlet, right-handed neutrino and their mirror chiral superfields is needed. Through the study of the minimization of the scalarpotential, the co

A. D. Kennedy, K. M. Bitar

We introduce a new Monte Carlo method for pure gauge theories. It is not intended for use with dynamical fermions. It belongs to the class of Local Hybrid Monte Carlo (LHMC) algorithms, which make use of the locality of the action by updating individual sites or links by following a classical mechanics trajectory in fictitious time. We choose to update a one

W. Bietenholz, U. -J. Wiese

The fixed point actions for Wilson and staggered lattice fermions are determined by iterating renormalization group transformations. In both cases a line of fixed points is found. Some points have very local fixed point actions. They can be used to construct perfect lattice actions for asymptotically free fermionic theories like QCD or the Gross-Neveu model.

Matt Visser

It is a deceptively simple question to ask how acoustic disturbances propagate in a non--homogeneous flowing fluid. If the fluid is barotropic and inviscid, and the flow is irrotational (though it may have an arbitrary time dependence), then the equation of motion for the velocity potential describing a sound wave can be put in the (3+1)--dimensional form: d

Jaegu Kim

The gravitational field of a moving point particle is obtained in a Lorentz covariant form for both uncharged and charged cases. It is shown that the general relativistic proper time interval at the location of the particle is the same as the special relativistic one and the gravitational and electromagnetic self forces are zero.

Eugene Wong, Ian Affleck

Tunneling through a localized barrier in a one-dimensional interacting electron gas has been studied recently using Luttinger liquid techniques. Stable phases with zero or unit transmission occur, as well as critical points with universal fractional transmission whose properties have only been calculated approximately, using a type of ``$ε$-expansion'&#3

Lizeng Zhang, Geoff Canright, Ted Barnes

We present a new quantum Monte Carlo algorithm suitable for generically complex problems, such as systems coupled to external magnetic fields or anyons in two spatial dimensions. We find that the choice of gauge plays a nontrivial role, and can be used to reduce statistical noise in the simulation. Furthermore, it is found that noise can be greatly reduced b

Subir Sachdev

We examine phases of the Shraiman-Siggia model of lightly-doped, square lattice quantum antiferromagnets in a self-consistent, two-loop, interacting magnon analysis. We find magnetically-ordered and quantum-disordered phases both with and without incommensurate spin correlations. The quantum disordered phases have a pseudo-gap in the spin excitation spectrum

Joshua Wilkie, Paul Brumer

A generalized approach to the quantization of a large class of maps on a torus, i.e. quantization via the von Neumann Equation, is described and a number of issues related to the quantization of model systems are discussed. The approach yields well behaved mixed quantum states for tori for which the corresponding Schrodinger equation has no solutions, as wel

G. B. Dalton, G. Efstathiou, S. J. Maddox, W. J. Sutherland

We present redshifts for a sample of 229 clusters selected from the APM Galaxy Survey, 189 of which are new redshift determinations. Non-cluster galaxy redshifts have been rejected from this sample using a likelihood ratio test based on the projected and apparent magnitude distributions of the cluster fields. We test this technique using cluster fields in wh

Sorin Popescu, Kristian Ranestad

The paper discusses the classification of surfaces of degree 10 and sectional genus 9 and 10. The surfaces of degree at most 9 are described through classical work dating from the last century up to recent years, while surfaces of degree 10 and other sectional genera are studied elsewhere. We use relations between multisecants, linear systems, syzygies and l

Charles Walter

Let $S$ be a birationally ruled surface. We show that the moduli schemes $M_S(r,c_1,c_2)$ of semistable sheaves on $S$ of rank $r$ and Chern classes $c_1$ and $c_2$ are irreducible for all $(r,c_1,c_2)$ provided the polarization of $S$ used satisfies a simple numerical condition. This is accomplished by proving that the stacks of prioritary sheaves on $S$ of

M. A. R. Osorio, M. A. Vazquez-Mozo

We study the cosmological meaning of duality symmetry by considering a two dimensional model of string cosmology. We find that as seen by an internal observer in this universe, the scale factor rebounds at the self-dual length. This rebound is a consequence of the adiabatic expansion. Furthermore, in this situation there are four mathematically different sce

G. P. Korchemsky

We consider elastic quark-quark scattering at high energy and fixed transferred momentum. Performing factorization of soft gluon exchanges into Wilson lines vacuum expectation values and studying their properties, we find that the asymptotics of the scattering amplitude is controlled by the renormalization properties of the so called cross singularities of W

D. I. Olive, E. Rabinovici, A. Schwimmer

A class of string backgrounds associated with non semi-simple groups is obtained as a special large level limit of ordinary WZW models. The models have an integer Virasoro central charge and they include the background recently studied by Nappi and Witten.

Nobuyuki Sakai, Kei-ichi Maeda

We complete a classification of junctions of two Friedmann-Robertson-Walker space-times bounded by a spherical thin wall. Our analysis covers super-horizon bubbles and thus complements the previous work of Berezin, Kuzumin and Tkachev. Contrary to sub-horizon bubbles, various topology types for super-horizon bubbles are possible, regardless of the sign of th

Ken-ichiro Arita, Kenichi Matsuyanagi

An oscillatory pattern in the smoothed quantum spectrum, which is unique for single-particle motions in a reflection-asymmetric superdeformed oscillator potential, is investigated by means of the semiclassical theory of shell structure. Clear correspondence between the oscillating components of the smoothed level density and the classical periodic orbits is

Martin Goldstern, Miroslav Repicky, Saharon Shelah, Otmar Spinas

Let l^0 and m^0 be the ideals associated with Laver and Miller forcing, respectively. We show that add (l^0) < cov(l^0) and add (m^0) < cov(m^0) are consistent. We also show that both Laver and Miller forcing collapse the continuum to a cardinal <= h .

Bradd Hart, Claude Laflamme, Saharon Shelah

We present a general framework for carrying out some constructions. The unifying factor is a combinatorial principle which we present in terms of a game in which the first player challenges the second player to carry out constructions which would be much easier in a generic extension of the universe, and the second player cheats with the aid of Diamond. Sect

James E. Baumgartner

A variety of classes of naturally arising ultrafilters on omega is discussed, and the question is raised whether it is consistent that the classes are empty. Since all the classes contain the P-point ultrafilters, a negative answer would greatly extend the famous theorem of Shelah.

Daniel Talayco

We explore an application of homological algebra to set theoretic objects by developing a cohomology theory for Hausdorff gaps. The cohomology theory is introduced with enough generality to be applicable to other questions in set theory. For gaps, this leads to a natural equivalence notion about which we answer questions by constructing many simultaneous gap

R. C. Myers, V. Periwal

Recent advances in non-critical string theory allow a unique continuation of critical Polyakov string amplitudes to off-shell momenta, while preserving conformal invariance. These continuations possess unusual, apparently stringy, characteristics, as we illustrate with our results for three-point functions. (Talk by R.C.M. at Strings &#39;93)

David N. Yetter

Motivated by suggestions of Paolo Cotta-Ramusino&#39;s work at the physical level of rigor relating BF theory to the Donaldson polynomials, we provide a construction applicable to the Turaev/Viro and Crane/Yetter invariants of *a priori* finer invariants dependent on a choice of (co)homology class on the manifold

E. Elizalde, S. Naftulin, S. D. Odintsov

A theory of higher-derivative 2D dilaton gravity which has its roots in the massive higher-spin mode dynamics of string theory is suggested. The divergences of the effective action to one-loop are calculated, both in the covariant and in the conformal gauge. Some technical problems which appear in the calculations are discussed. An interpretation of the theo

Giovanni Modanese

In the weak field expansion of euclidean quantum gravity, an analysis of the Wilson loops in terms of the gauge group, $SO(4)$, shows that the correspondent statistical system does not develope any configuration with localized curvature at low temperature. Such a ``non-local&#39;&#39; behavior contrasts strongly with that of usual gauge fields. We point out

J. E. Cieza Montalvo, O. J. P. Eboli

We analyze systematically the signatures of vector leptoquarks in hadronic collisions. We examine their single and pair productions, as well as their effects on the production of lepton pairs. Our results indicate that a machine like the CERN Large Hadron Collider (LHC) will be able to unravel the existence of vector leptoquarks with masses up to the range o

Alejandro Ayala, Jamal Jalilian--Marian, Larry McLerran, Axel P. Vischer

We investigate the motion of fermions in the presence of an electro\-weak phase transition bubble wall. We derive and solve the Dirac equation for such fer\-mions, and compute the transmission and reflection coefficients for fermions traveling from the symmetric to the asymmetric phases separated by the domain wall.

A. A. Bel&#39;kov, G. Bohm, F. Matthäi, A. V. Lanyov

We give a simple expression in linear and quadratic Dalitz--plot slopes which does not depend on the charge combination of the $3π$ state $(K^\pm \to π^{\pm}π^{+}π^{-}$ or $π^{\pm}π^{0}π^{0}$ and $K_L^{0} \to π^{+}π^{-}π^{0}$ or $π^{0}π^{0}π^{0})$, if all phases between final states are negligible. After investigating the influence of radiative corrections,

S. Bertolini, F. Vissani

We consider a class of N=1 supersymmetric extensions of the Standard Model in which the soft breaking sector is CP conserving at the GUT scale. We study the question of whether the presence of explicit CP violation in the Yukawa sector of the theory induces through renormalization effects CP violating phases in the soft terms, which could lead to observable

F. M. Steffens, V. E. Herscovitz

We treat the Skyrme model with the breathing mode in a situation involving two quartic terms. It is seen that there is a new limit for large $e$ due to the breathing mode not found in the usual rotating hedgehog.

Thomas M. Gould, Stephen D. H. Hsu

We examine the spacetime symmetries of forward $2 \rightarrow 2$ scattering. These symmetries have non-trivial consequences for any class of configurations which might dominate the amplitude in the semiclassical approximation. We derive some dynamical results regarding the stability of configurations which arise solely from reflection symmetry and positivity

R. Narayanan, H. Neuberger

An expression for the lattice effective action induced by chiral fermions in any even dimensions in terms of an overlap of two states is shown to have promising properties in two and four dimensions: The correct abelian anomaly is reproduced and gauge field configurations with non-zero topological charge are completely suppressed.

Rajamani Narayanan

I present the recent developments in a specific sub-field of chiral gauge theories on the lattice. This sub-field pertains to the use of infinitely many fermi fields to describe a single chiral field. In this approach, both anomalous and anomaly free theories can be discussed in equal footing. It produces the correct anomaly in the continuum limit. It has th

R. Altmeyer, M. Goeckeler, R. Horsley, E. Laermann

We will discuss here an indirect lattice evaluation of the baryon axial singlet current matrix element. This quantity may be related to the fraction of nucleon spin carried by the quarks. The appropriate structure function has recently been measured (EMC experiment). As in this experiment, we find that the quarks do not appear to carry a large component of t