May 1994 arXiv papers — page 6

Felix Schlumpf

We demonstrate that a relativistic constituent quark model can give nucleon form factors that agree well with recent, accurate measurements. The relativistic features of the model and the specific form of the wave function are essential for the result. (Talk given at 14th International Conference on Few-Body Problems in Physics, Williamsburg, Virginia, USA,

P. H. Chankowski, R. Hempfling, S. Pokorski

The leptonic $τ$ decays are calculated at the 1-loop level in the Minimal Supersymmetric Standard Model. The deviation from the $τ- μ- e$ universality is studied as a function of the supersymmetric parameters and discussed in the context of the expected improvement of the experimental accuracy.

The SLD Collaboration

Using an impact parameter tag to select an enriched sample of $Z \rightarrow b \overline{b}$ events, we have measured the difference between the average charged multiplicity of $Z \rightarrow b \overline{b}$ and $Z^0 \rightarrow hadrons$ to be $\overline{n}_{b} - \overline{n}_{had} = 2.24\pm 0.30(\rm{stat.}) \pm 0.33(\rm{syst.})$ tracks per event. {}From thi

J. Barrette

Event shapes for Au + Au collisions at 11.4 GeV/c per nucleon were studied over nearly the full solid angle with the E877 apparatus. The analysis was performed by Fourier expansion of azimuthal distributions of the transverse energy (E_T) measured in different pseudorapidity intervals. For semicentral collisions a pronounced event anisotropy is identified be

D. Korotkin, H. Nicolai

The Ernst equation is formulated on an arbitrary Riemann surface. Analytically, the problem reduces to finding solutions of the ordinary Ernst equation which are periodic along the symmetry axis. The family of (punctured) Riemann surfaces admitting a non-trivial Ernst field constitutes a ``partially discretized'' subspace of the usual moduli space. T

Th. M. Nieuwenhuizen, M. C. W. van Rossum

The distributions of the angular transmission coefficient and of the total transmission are calculated for multiple scattered waves. The calculation is based on a mapping to the distribution of eigenvalues of the transmission matrix. The distributions depend on the profile of the incoming beam. The distribution function of the angular transmission has a stre

N. Provatas, T. Ala-Nissila, Martin Grant, K. R. Elder

We introduce a phase-field model to describe the dynamics of a self-sustaining propagating combustion front within a medium of randomly distributed reactants. Numerical simulations of this model show that a flame front exists for reactant concentration $c > c^* > 0$, while its vanishing at $c^*$ is consistent with mean-field percolation theory. For $c > c^*$

Elmar S. Heeb, T. Maurice Rice

By combining a generalized Lanczos scheme with the variational Monte Carlo method we can optimize the short- and long-range properties of the groundstate separately. This allows us to measure the long-range order of the groundstate of the $t$-$J$ model as a function of the coupling constant $J/t$, and identify a region of finite d-wave superconducting long-r

Holger Frahm, Vladimir I. Inozemtsev

Starting from a Calogero--Sutherland model with hyperbolic interaction confined by an external field with Morse potential we construct a Heisenberg spin chain with exchange interaction $\propto 1/\sinh^2 x$ on a lattice given in terms of the zeroes of Laguerre polynomials. Varying the strength of the Morse potential the Haldane--Shastry and harmonic spin cha

Tomo Munehisa, Yasuko Munehisa

We present detailed discussions on a new approach we proposed in a previous paper to numerically study quantum spin systems. This method, which we will call re-structuring method hereafter, is based on rearrangement of intermediate states in the path integral formulation. We observed our approach brings remarkable improvement in the negative sign problem whe

J. I. Katz

The delayed hard (up to 25 GeV) photons observed more than an hour following a gamma-ray burst on February 17, 1994 may result from the collisions of relativistic nucleons with a dense cloud, producing $π^0$. The required cloud density is $\sim 2 \times 10^{11}$ cm$^{-3}$. This cloud may be the remains of the disrupted envelope of a neutron star, and may sur

M. G. Haehnelt

Supermassive black holes are investigated as possible sources for low-frequency bursts of gravity waves. The event rate for `known' supermassive black holes at intermediate and high redshifts, inferred from the quasar luminosity function, is low $\sim 0.1 \yr^{-1}$. A space-based interferometer could therefore only see several events per year from superm

S. Antonelli, M. Bellacci, L. A. Fernández, A. Muñoz-Sudupe

The polarization of Polyakov type loops is responsible for the difference between quenched and unquenched finite size effects on the QCD mass spectrum. With a numerical simulation, using different sea quarks boundary conditions, we show that we can align the spatial Polyakov loops in a predefined direction. Starting from these results, we propose a procedure

David Kaiser

Recent experimental determinations of the spectral index describing the scalar mode spectrum of density perturbations encourage comparison with predictions from models of the very early universe. Unlike extended inflation, Induced-gravity Inflation predicts a power spectrum with $0.98 \leq n_s \leq 1.00$, in close agreement with the experimental measurements

Stephan Kehrein, Andreas Mielke

Using a continuous unitary transformation recently proposed by Wegner \cite{Wegner} together with an approximation that neglects irrelevant contributions, we obtain flow equations for Hamiltonians. These flow equations yield a diagonal or almost diagonal Hamiltonian. As an example we investigate the Anderson Hamiltonian for dilute magnetic alloys. We study t

F. J. Botella, S. Noguera, J. Portoles

Non--resonant decays of charmed mesons into three pseudoscalars are analyzed in a weak gauged $U(4)_L \otimes U(4)_R$ chiral lagrangian model. The calculation is free of unknown parameters and only requires the masses of pseudoscalar mesons as hadronic inputs. When comparison with experimental data is possible we find that in some processes we have good agre

Tonatiuh Matos

We give a methodology for solving the chiral equations $(\alpha g_{,z} g^{-1})_{,\overline z} + (\alpha g_{,\overline z} g^{-1})_{,z} \ = \ 0 $ where $g$ belongs to some Lie group $G$. The solutions are writing in terms of Harmonic maps. The method could be used even for some infinite Lie groups. (Preprint CIEA-gr-94/06)

H. Garcia-Compean, J. F. Plebanski, M. Przanowski

We generalize the geometric structures generated by Witten's ground ring. It is shown that these generalized structures involve in a natural way some geometric constructions from Self-dual gravity [1,12]. The formal twistor construction on full quantum ground ring manifold is also given.

Ben Dorman, Robert W. O'Connell, Robert T. Rood

We present an analysis of the far-ultraviolet upturn phenomenon (UVX) observed in elliptical galaxies and spiral galaxy bulges. Our premise is that the UV radiation from these systems emanates primarily from extreme horizontal branch (EHB) stars and their progeny. We re-derive the broad-band UV colors $1500-V$ and $2500-V$ for globular clusters and elliptica

P. Kondratowicz, P. Podles

Irreducible representations of quantum groups $SL_q(2)$ (in Woronowicz' approach) were classified in J.Wang, B.Parshall, Memoirs AMS 439 in the~case of $q$ being an~odd root of unity. Here we find the~irreducible representations for all roots of unity (also of an~even degree), as well as describe "the~diagonal part" of tensor product of any two i

H. B. O'Connell, B. C. Pearce, A. W. Thomas, A. G. Williams

Within a broad class of models we show that the amplitude for rho^0-omega mixing must vanish at the transition from timelike to spacelike four momentum. Hence in such models the mixing is either zero everywhere or is necessarily momentum-dependent. This lends support to the conclusions of other studies of rho-omega mixing and calls into question standard ass

Juris Steprāns

This is a revision (and partial retraction) of my previous abstarct. Let $λ(X)$ denote Lebesgue measure. If $X\subseteq [0,1]$ and $r \in (0,1)$ then the $r$-Hausdorff capacity of $X$ is denoted by $H^r(X)$ and is defined to be the infimum of all $\sum_{i=0}^\infty λ(I_i)^r$ where $\{I_i\}_{i\inω}$ is a cover of $X$ by intervals. The $r$ Hausdorff capacity h

J. Harnad, P. Winternitz

The relation between solutions to Helmholtz's equation on the sphere $S^{n-1}$ and the $[{\gr sl}(2)]^n$ Gaudin spin chain is clarified. The joint eigenfuctions of the Laplacian and a complete set of commuting second order operators suggested by the $R$--matrix approach to integrable systems, based on the loop algebra $\wt{sl}(2)_R$, are found in terms o

Silvio J. Rabello, Carlos Farina

Using a gauge covariant operator technique we deduce the path integral for a charged particle in a stationary magnetic field, verifying the "midpoint rule" for the discrete form of the interaction term with the vector potential.

K. Zarembo

The lattice model of principal chiral field interacting with the gauge fields, which have no kinetic term, is considered. This model can be regarded as a strong coupling limit of lattice gauge theory at finite temperature. The complete set of equations for collective field variables is derived in the large N limit and the phase structure of the model is stud

J. F. Plebański, H. García-Compeán

\noindent It is find a non-linear partial differential equation which we show contains the first Heavenly equation of Self-dual gravity and generalize the second one. This differential equation we call "Weak Heavenly Equation" (${\cal WH}$-equation). For the two-dimensional case the ${\cal WH}$-equation is brought into the evolution form (Cauchy-Kova

Patrick Huet

I report a recent study done in collaboration with M.E. Peskin, on the time dependence of a kaon beam propagating according to a generalization of quantum mechanics due to Ellis, Hagelin, Nanopoulos and Srednicki, in which CP- and CPT-violating signatures arise from the evolution of pure states to mixed states. Constraints on the magnitude of its parameters

Yuval Kluger

We study the dynamics of the chiral phase transition expected during the expansion of the quark-gluon plasma produced in a high energy hadron or heavy ion collision in the $O(4)$ linear sigma model to leading order in a large $N$ expansion for strong coupling constants. Starting from an approximate equilibrium configuration at an initial proper time $τ$ in t

J. Lopez

In these lectures I review the progress made over the last few years in the subject of string and string-inspired phenomenology. I take a practical approach, thereby concentrating more on explicit examples rather than on formal developments. Topics covered include: introduction to string theory, the free-fermionic formulation and its general features, generi

Douglas O. Carlson, Ehab Malkawi, C. --P. Yuan

We parameterize the non-universal couplings of t-t-Z and t-b-W in the electroweak chiral lagrangian approach, and examine the constraints on these parameters from the LEP data. We also study how the SLC, Tevatron, LHC and NLC can improve the measurement of these couplings. Different symmetry breaking scenarios imply different correlations among these couplin

Ravi Kuchimanchi

We propose that the physics beyond the standard Weinberg-Salam model is such that matter and the CP conjugate anti-matter fields have the same set of charges with respect to the various force groups (upto ordering). We show that this CP-like symmetry leads to an understanding of family replication. We use anomaly constraints to infer the fermion spectra that

R. Sekhar Chivukula, Vassillis Koulovassilopoulos

The one-Higgs-doublet standard model is necessarily incomplete because of the triviality of the scalar symmetry-breaking sector. If the Higgs mass is approximately 600 GeV or higher, there must be additional dynamics at a scale $Λ$ which is less than a few TeV. In this case the properties of the Higgs resonance can differ substantially from those predicted b

Markus A. Luty, John March-Russell, Martin White

We consider the baryon octet and decuplet magnetic moments in a simultaneous expansion in $m_s$ and $1/N$ taking $N_F / N \sim 1$, where $N$ is the number of QCD colors and $N_F$ is the number of light quark flavors. At leading order in this expansion, the magnetic moments obey the non-relativistic quark-model relations. We compute corrections to these relat

Markus A. Luty

Using recently-developed diagrammatic techniques, I derive some general results concerning baryons in the $1/N$ expansion, where $N$ is the number of QCD colors. I show that the spin-flavor relations which hold for baryons in the large-$N$ limit, as well as the form of the corrections to these relations at higher orders in $1/N$, hold even if $N_F / N \sim 1

Jin Dai

We propose a new method of extracting $V_{bu}$ from measurements of Semi-leptonic B decay which has much less theoretical uncertainties than conventional methods.

D. Allouani, H. Kröger

We consider a fractal Wilson loop $<F_{P}>$ and present physical arguments why this should be a relevant observable in nature. We show for non-compact SU(2) lattice gauge theory in the next to leading order of strong coupling expansion that $<F_{P}>$ obeys an area law behavior and is gauge invariant.

A. Ashtekar, R. Loll

Since the gauge group underlying 2+1-dimensional general relativity is non-compact, certain difficulties arise in the passage from the connection to the loop representations. It is shown that these problems can be handled by appropriately choosing the measure that features in the definition of the loop transform. Thus, ``old-fashioned&#39;&#39; loop represen

Jan de Boer, Vladimir E. Korepin, Andreas Schadschneider

We consider extended versions of the Hubbard model which contain additional interactions between nearest neighbours. In this letter we show that a large class of these models has a superconducting ground state in arbitrary dimensions. In some special cases we are able to find the complete phase diagram. The superconducting phase exist even for moderate repul

Dean Prichard, James Theiler

We propose an extension to multivariate time series of the phase-randomized Fourier-transform algorithm for generating surrogate data. Such surrogate data sets must mimic not only the autocorrelations of each of the variables in the original data set, they must mimic the cross-correlations {\em between} all the variables as well. The method is applied both t

Frederick H. Willeboordse, Kunihiko Kaneko

A novel type of self-organized lattice in which chaotic defects are arranged periodically is reported for a coupled map model of open flow. We find that temporally chaotic defects are followed by spatial relaxation to an almost periodic state when suddenly a next defect appears. The distance between successive defects is found to be generally predetermined a

E. E. Fenimore, J. G. Laros, A. Ulmer

Soft Gamma Repeaters (SGRs) are a class of rare, high-energy galactic transients that have episodes of short (~0.1 sec), soft (~30 keV), intense (~100 Crab), gamma-ray bursts. We report an analysis of the x-ray emission from 95 SGR1806-20 events observed by the International Cometary Explorer. The spectral shape remains remarkably constant for bursts that di

K. Strobl, T. J. Weiler

We present analytic solutions to the spatially homogeneous axion field equation, using a model potential which strongly resembles the standard anharmonic $(1-\cos Nθ)$ potential, but contains only a piece-wise second order term. Our exactly soluble model for $θ(t)$ spans the entire range $[-π/N,π/N]$. In particular, we are able to confirm (i) Turner&#39;s nu

Bernard J. Carr, Jonathan H. Gilbert, James E. Lidsey

Blue primordial power spectra have spectral index $n>1$ and arise naturally in the recently proposed hybrid inflationary scenario. An observational upper limit on {\em n} is derived by normalizing the spectrum at the quadrupole scale and considering the possible overproduction of Planck mass relics formed in the final stage of primordial black hole evaporati

J. F. L. Simmons, A. Newsam, M. A. Hendry

Although Potent purports to use only radial velocities in reconstructing the potential velocity field of galaxies, the derivation of transverse components is implicit in the smoothing procedures adopted. Thus the possibility arises of using nonradial line integrals to derive a smoothed velocity field. For an inhomogeneous galaxy distribution the optimal path

Yakov Karpishpan

In \cite{K} we introduced two variants of higher-order differentials of the period map and showed how to compute them for a variation of Hodge structure that comes from a deformation of a compact Kähler manifold. More recently there appeared several works (\cite{BG}, \cite{EV}, \cite{R}) defining higher tangent spaces to the moduli and the corresponding high

V. Gurarie

We apply the methods of Field Theory to study the turbulent regimes of statistical systems. First we show how one can find their probability densities. For the case of the theory of wave turbulence with four-wave interaction we calculate them explicitly and study their properties. Using those densities we show how one can in principle calculate any correlati

J. Sobczyk

A problem of constructing quantum groups from classical r-matrices is discussed.

P. Kosi{ń}ski, J. Lukierski, P. Ma{ś}lanka, J. Sobczyk

The classical $r$-matrix for $N=1$ superPoincar{\'e} algebra, given by Lukierski, Nowicki and Sobczyk is used to describe the graded Poisson structure on the $N=1$ Poincar{\'e} supergroup. The standard correspondence principle between the even (odd) Poisson brackets and (anti)commutators leads to the consistent quantum deformation of the superPoincar{\'e} gr

J. J. Lodder, H. J. de Blank

The newly published top mass prediction of 85.1 GeV conflicts with indirect limits on the top mass, based on precision measurements interpreted by calculations using dimensional regularization. The top quark contribution to part of the electroweak W and Z vacuum polarization tensor is recomputed using the symmetrical theory of generalised functions. The squa

U. Bleyer, A. Zhuk

Multidimensional cosmological models with $n (n > 1)$ spaces of constant curvature are discussed classically and with respect to canonical quantization. These models are integrable in the case of Ricci flat internal spaces. For positive curvature in the external space we find exact solutions modelling dynamical as well as spontaneous compactification of inte

Jerzy F. Plebanski, H. Garcia-Compean

Using a $q$-deformed Moyal algebra associated with the group of area preserving diffeomorphisms of th two-dimensional torus $T^2$, sdiff$_q (T^2)$, a $q$-deformed version for the Heavenly equations is given. Finally, the two-dimensional chiral version of Self-dual gravity in this $q$-deformed context is briefly discussed.

M. J. Musolf, R. Schiavilla, T. W. Donnelly

Meson-exchange current (MEC) contributions to the parity-violating (PV) asymmetry for elastic scattering of polarized electrons from $^4$He are calculated over a range of momentum transfer using Monte Carlo methods and a variational $^4$He ground state wavefunction. The results indicate that MEC&#39;s generate a negligible contribution to the asymmetry at lo

M. V. STOITSOV, P. RING, M. M. SHARMA

The breathing-mode giant monopole resonance (GMR) is studied within the framework of the relativistic mean-field theory using the Generator Coordinate Method (GCM). The constrained incompressibility and the excitation energy of isoscalar giant monopole states are obtained for finite nuclei with various sets of Lagrangian parameters. A comparison is made with

J. Bonet, Jari Taskinen

We construct a countable inductive limit of weighted Banach spaces of holomorphic functions, which is not a topological subspace of the corresponding weighted inductive limit of spaces of continuous functions. The main step of our construction, using a special sequence of outer holomorphic functions, shows that a certain sequence space is isomorphic to a com

P. Pasti, M. Tonin

The twistor--like formulation of the type IIA superstring $σ$--model in D=10 is obtained by performing a dimensional reduction of the recently proposed twistor--like action of the supermembrane in D=11. The superstring action is invariant under local, worldsheet $(n,n)$ supersymmetry where $3\leq n \leq 8$ and is classical equivalent to the standard Green--S

S. Kojima, N. Sakai, Y. Tanii

Quantum theory of dilaton gravity is studied in $2+ε$ dimensions. Divergences are computed and renormalized at one-loop order. The mixing between the Liouville field and the dilaton field eliminates $1/ε$ singularity in the Liouville-dilaton propagator. This smooth behavior of the dilaton gravity theory in the $ε\rightarrow 0$ limit solves the oversubtractio

Marcelo Gleiser

Electroweak baryogenesis may solve one of the most fundamental questions we can ask about the universe, that of the origin of matter. It has become clear in the past few years that it also poses a multi-faceted challenge. In order to compute the tiny primordial baryonic excess, we probably must invoke physics beyond the standard model (an exciting prospect f

Rudolph C. Hwa, Jicai Pan

The problem of hadronic cluster production in heavy-ion collisions is studied in search for an observable signature of first-order quark-hadron phase transition. The study is carried out by cellular automata in a two-dimensional model of the mixed phase at midrapidity. The clusters are allowed to grow as well as to coalesce upon collision. The distribution o

J. Kroll, B. Schwesinger

In the SU3 Skyrme model the electric quadrupole moments of $\frac{3}{2}^+$ baryons show a strong sensitivity with respect to flavor distortions in baryon wavefunctions. SU3 symmetric wavefunctions lead to quadrupole moments proportional to the charge of the baryon whereas for strongly broken flavor symmetry a proportionality to baryonic isospin emerges. Sinc

Dieter Schildknecht

We reemphasize the importance of discriminating fermion-loop and bosonic electroweak corrections in the analysis of electroweak precision data. Most recent data are indeed precise enough to require corrections beyond (trivial) fermion loops. An analysis of these data in terms of the observables $Δx \equiv ε_{N1} - ε_{N2}$, $Δy \equiv - ε_{N2}$ and $ε\equiv -

J. J. Lodder

The bosonic contributions to the photon mass are shown to be of the same form as the fermionic contributions, but of opposite sign. A mass sum rule for bosons and fermions follows from gauge invariance. Assuming completeness of the standard model the top quark mass can be predicted. Effectively only the W-bosons contribute, giving a lowest order prediction o

O. K. Kalashnikov

It is shown that the fictitious infrared pole is eliminated from the hot gauge theory which acquires a new vacuum after the global gauge symmetry spontaneously breaking. The nonzero W-condensate is generated and leads to the screening of the chromomagnetic forces through the scenario with the standard magnetic mass.

J. Ambjorn, J. Jurkiewicz

Simplicial quantum gravity has been proposed as a regularization for four dimensional quantum gravity. The partition function is constructed by performing a weighted sum over all triangulations of the 4-sphere. The model is well-defined only if the number of such triangulations consisting of $N$ simplexes is exponentially bounded. Numerical simulations seem

Nichol C. Brummer

Parity violation at LEP or SLC can be measured through the charge asymmetry. An optimal method of moments is developed here to measure this asymmetry, as well as similar asymmetries. This method is equivalent to the likelihood fit. It is simpler in use, as it gives analytical formulas for both the asymmetry and its statistical error. These formulas give the

Nichol. C. Brummer

Experimental data on the shape of hadronic momentum spectra are compared with theoretical predictions in the context of calculations in the Modified Leading Log Approximation (MLLA), under the assumption of Local Parton Hadron Duality (LPHD). Considered are experimental measurements at $e^+e^-$-colliders of $ξ_p^*$, the position of the maximum in the distrib

J. N. Goldberg, D. C. Robinson

Newman and Rovelli have used singular Hamilton-Jacobi transformations to reduce the phase space of general relativity in terms of the Ashtekar variables. Their solution of the gauge constraint cannot be inverted and indeed has no Minkowski space limit. Nonetheless, we exhibit an explicit Hamilton-Jacobi solution of all the linearized constraints. The result

Chris Isham, Noah Linden

We analyse and develop the recent suggestion that a temporal form of quantum logic provides the natural mathematical framework within which to discuss the proposal by Gell-Mann and Hartle for a generalised form of quantum theory based on the ideas of histories and decoherence functionals. Particular stress is placed on properties of the space of decoherence

Daniel Koller, Michael C. Martin, Laszlo Mihaly

Optical measurements on doped C$_{60}$ films provide evidence for a transition from a high temperature conducting phase to a low temperature insulating phase in quenched Rb$_1$C$_{60}$ and K$_1$C$_{60}$ compounds, while Cs$_1$C$_{60}$ did not exhibit this behavior. For slow cooled samples our study confirms earlier results indicating phase separation of K$_1

Michael N. Kiselev

In the framework of the two-band model of a doped semiconductor the self-consistent equations describing the transition into the excitonic insulator state are obtained for the 2D case. It is found that due to the exciton-electron interactions the excitonic phase may arise with doping in a semiconductor stable initially with respect to excitonic transition in

Silvio R. Dahmen

The master equation of one-dimensional three-species reaction-diffusion processes is mapped onto an imaginary-time Schrödinger equation. In many cases the Hamiltonian obtained is that of an integrable quantum chain. Within this approach we search for all $3$-state integrable quantum chains whose spectra are known and which are related to diffusive-reactive s

E. Aurell, G. Boffetta, A. Crisanti, P. Frick

We study shell models that conserve the analogues of energy and enstrophy, hence designed to mimic fluid turbulence in 2D. The main result is that the observed state is well described as a formal statistical equilibrium, closely analogous to the approach to two-dimensional ideal hydrodynamics of Onsager, Hopf and Lee. In the presence of forcing and dissipati

Bruce W. Roberts, Eberhard Bodenschatz, James P. Sethna

We present a calculation of defect--defect correlation functions in the defect turbulence regime of the complex Ginzburg--Landau equation. Our results do not agree with the predictions of generic scale invariance. Using the topological nature of the defects, we prove that defect--defect correlations cannot decay as slowly as predicted by generic scale invari

Brian Fields, Keith Olive, David Schramm

To understand better the early galactic production of Li, Be, and B by cosmic ray spallation and fusion reactions, the dependence of these production rates on cosmic ray models and model parameters is examined. The sensitivity of elemental and isotopic production to the cosmic ray pathlength magnitude and energy dependence, source spectrum, spallation kinema

A. Kashlinsky, I. I. Tkachev, J. Frieman

We study the microwave background anisotropy due to superhorizon-size perturbations (the Grischuk-Zel&#39;dovich effect) in open universes with negative spatial curvature. Using COBE results on the low-order temperature multipole moments, we find that if the homogeneity of the observable Universe arises from an early epoch of inflation, the present density p

Ian Smail, Warrick J. Couch, Richard S. Ellis, Ray M. Sharples

Deep Hubble Space Telescope images of superlative resolution obtained for the distant rich cluster AC114 (z=0.31) reveal a variety of gravitational lensing phenomena for which ground-based spectroscopy is available. We present a luminous arc which is clearly resolved by HST and appears to be a lensed z=0.64 sub-L star spiral galaxy with a detected rotation c

Keith A. Olive, Gary Steigman

We have used recent observations of helium-4, nitrogen and oxygen from some four dozen, low metallicity, extra-galactic HII regions to define mean $N$ versus $O$, $^4He$ versus $N$ and $^4He$ versus $O$ relations which are extrapolated to zero metallicity to determine the primordial $^4He$ mass fraction $Y_P$. The data and various subsets of the data, select

V. P. Gusynin, V. A. Miransky, I. A. Shovkovy

It is shown that in $2+1$ dimensions, a constant magnetic field is a strong catalyst of dynamical flavor symmetry breaking, leading to generating a fermion dynamical mass even at the weakest attractive interaction between fermions. The effect is illustrated in the Nambu-Jona-Lasinio model in a magnetic field. The low-energy effective action in this model is

A. D. Dolgov, M. B. Einhorn, V. I. Zakharov

To resolve infrared problems with the de~Sitter invariant vacuum, we argue that the history of the de~Sitter phase is crucial. We illustrate how either (1)~the diagonalization of the Hamiltonian for long-wavelength modes or (2)~an explicit modification of the metric in the distant past leads to natural infrared cutoffs. The former case resembles a bosonic su

C. Gomez, E. Lopez

The special geometry ($(t,{\bar t})$-equations) for twisted $N=2$ strings are derived as consistency conditions of a new contact term algebra. The dilaton appears in the contact terms of topological and antitopological operators. The holomorphic anomaly, which can be interpreted as measuring the background dependence, is obtained from the contact algebra rel

A. Kempf

A noncommutative geometric generalisation of the quantum field theoretical framework is developed by generalising the Heisenberg commutation relations. There appear nonzero minimal uncertainties in positions and in momenta. As the main result it is shown with the example of a quadratically ultraviolet divergent graph in $ϕ^4$ theory that nonzero minimal unce

R. Kleiss, R. Pittau

We discuss the improvement in the accuracy of a Monte Carlo integration that can be obtained by optimization of the `a-priori weights&#39; of the various channels. These channels may be either the strata in a stratified-sampling approach, or the several `approximate&#39; distributions such as are used in event generators for particle phenomenology. The optim

Vortex String, Tomoko Ota, Ichiro Tsukada, Ichiro Terasaki

Current-voltage ($I-V$) characteristics and the increase of superconducting transition temperature $T_c$ as a function of the number of half-unit-cell layers $n$ are studied on Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+δ}$ thin films grown by molecular beam epitaxy. These observations are interpreted in terms of Kosterlitz-Thouless (KT) transition associated with vo

Andreas Stolcke, Jonathan Segal

We present an algorithm for computing n-gram probabilities from stochastic context-free grammars, a procedure that can alleviate some of the standard problems associated with n-grams (estimation from sparse data, lack of linguistic structure, among others). The method operates via the computation of substring expectations, which in turn is accomplished by so

Bumsig Kim

As a generalization of our previous paper [GK], we formulate a residue formula and some simple behaviors of equivariant quantum cohomology applying to compute the quantum cohomology of partial flag manifolds $F_{k_1,\cdots , k_l} $with a try to give a rigorous definition of equivariant quantum cohomology.

J. K. Freericks, Mark Jarrell

A strictly truncated (weak-coupling) perturbation theory is applied to the attractive Holstein and Hubbard models in infinite dimensions. These results are qualified by comparison with essentially exact Monte Carlo results. The second order iterated perturbation theory is shown to be quite accurate in calculating transition temperatures for retarded interact

T. Engeland, M. Hjorth-Jensen, A. Holt, E. Osnes

We comment upon a recent work by Zheng, Barrett, Jaqua, Vary and McCarthy, concerning calculations of spectra of light nuclei with no core. It is demonstrated that the omission of particle-particle ladder diagrams in their calculations, explains the large differences between results obtained with various model spaces.

K. Saito, A. W. Thomas

The quark-meson coupling model which we have developed previously is extended to incorporate the $\delta$ meson. It is then used to study the Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter. We find that, in combination with the {\it u-d\/} mass difference, the difference between quark scalar densities in protons and neutrons generates

Dean L. Welch

Several stationary solutions of the low energy string equations are dualized with respect to their timelike symmetry. Many of the duals have simple physical interpretations. Those of the nonextremal three dimensional black hole and black string are negative mass black strings. The extremal cases of these, and extremal higher dimensional black strings also, g

Charles B. Thorn

We argue that string theory should have a formulation for which stability and causality are evident. Rather than regard strings as fundamental objects, we suggest they should be regarded as composite systems of more fundamental point-like objects. A tentative scheme for such a reinterpretation is described along the lines of &#39;t Hooft&#39;s $1/N$ expansio

C. Bachas, C. de Calan, P. M. S. Petropoulos

Spin models on quenched random graphs are related to many important optimization problems. We give a new derivation of their mean-field equations that elucidates the role of the natural order parameter in these models.

R. Brustein

Superstring theory predicts the existence of a scalar field, the dilaton. I review some basic features of the dilaton interactions and explain their possible consequences in cosmology and particle physics.

Sergio Ferrara

A recollection of some theoretical developments that preceded and followed the first formulation of supergravity theory is presented. Special emphasis is placed on the impact of supergravity on the search for a unified theory of fundamental interactions.

Friedemann Brandt

It is shown that Bäcklund transformations (BTs) and zero-curvature representations (ZCRs) of systems of partial differential equations (PDEs) are closely related. The connection is established by nonlinear representations of the symmetry group underlying the ZCR which induce gauge transformations relating different BTs. This connection is used to construct B

G. H. Gadiyar

It is well known that magnetic monopoles are related to the first Chern class. In this note electric charge is used to construct an analogous characteristic class: the charge class.

Hideaki Hiro-Oka, Hisakazu Minakata

We examine one-dimensional Bose gas interacting with delta-function potential using the large-$N$ collective field theory. We show that in the case of attractive potential the uniform ground state is unstable to small perturbations and the instability is cured by formation of a collective ground state, \lq\lq bright soliton&#39;&#39; configuration in corresp

G. H. Gadiyar

The possibility of control of phenomena at microscopic level compatible with quantum mechanics and quantum field theory is outlined. The theory could be used in nanotechnology.

N. Shtykov

We compute the one-loop potential (the Casimir energy) for scalar, spinor and vectors fields on the spaces $\,R^{m+1}\, \times\,Y$ with $\,Y=\,S^N\,,CP^2$. As a physical model we consider spinor electrodynamics on four-dimensional product manifolds. We examine the cancelation of a divergent part of the Casimir energy on even-dimensional spaces by means of in

Jun Nishimura, Shinya Tamura, Asato Tsuchiya

We study $R^2$ gravity in $(2+ε)$--dimensional quantum gravity. Taking care of the oversubtraction problem in the conformal mode dynamics, we perform a full order calculation of string susceptibility in the $ε\rightarrow 0$ limit. The result is consistent with that obtained through Liouville approach.

O. Foda, K. Iohara, M. Jimbo, R. Kedem

We discuss a construction of highest weight modules for the recently defined elliptic algebra ${\cal A}_{q,p}(\widehat{sl}_2)$, and make several conjectures concerning them. The modules are generated by the action of the components of the operator $L$ on the highest weight vectors. We introduce the vertex operators $Φ$ and $Ψ^*$ through their commutation rel

Kingman Cheung, Tzu Chiang Yuan

We calculate the process-independent fragmentation functions for a $\bar b$ antiquark to fragment into longitudinally and transversely polarized $B_c^*$ ($^3S_1$) mesons to leading order in the QCD strong coupling constant. In the special case of equal quark mass we recover previous results for the fragmentation of $c\to ψ$ and $b\toΥ$. Various spin asymmetr