March 1998 arXiv papers — page 18

Eric J. Korpela, Stuart Bowyer

We present the results of searches for EUV emission from neutron stars conducted with the EUVE Deep Survey and Scanner Telescopes. To date, 21 fields containing known neutron stars have been observed in the Lexan/Boron (40--190 angstrom) band. Of these, 11 fields were simultaneously observed in the Aluminum/Carbon (160-385 angstrom) band. Five neutron stars

Konstadinos Sfetsos

In order to study quantum aspects of $\s$-models related by Poisson--Lie T-duality, we construct three- and two-dimensional models that correspond, in one of the dual faces, to deformations of $S^3$ and $S^2$. Their classical canonical equivalence is demonstrated by means of a generating functional, which we explicitly compute. We examine how they behave und

Randy Lewis, R. M. Woloshyn

The masses of spin-singlet and spin-triplet S-wave mesons containing a single heavy quark are computed in the quenched approximation. The light quark action and gauge field action are both classically-improved and tadpole-improved, and the couplings to the heavy quark are organized by the 1/M expansion of tadpole-improved NRQCD. At each of two lattice spacin

Alessandra Buonanno, Thibault Damour

We derive the effective action for classical strings coupled to dilatonic, gravitational, and axionic fields. We show how to use this effective action for: (i) renormalizing the string tension, (ii) linking ultraviolet divergences to the infrared (long-range) interaction between strings, (iii) bringing additional light on the special cancellations that occur

N. Furukawa, T. M. Rice

We examine a two-dimensional Fermi liquid with a Fermi surface which touches the Umklapp surface first at the 4 points $(\pm π/2, \pm π/2)$ as the electron density is increased. Umklapp processes at the 4 patches near $(\pm π/2, \pmπ/2)$ lead the renormalization group equations to scale to strong coupling resembling the behavior of a 2-leg ladder at half-fil

A. A. Andrianov, D. Espriu, R. Tarrach

We consider the low energy effective action of QCD below the chiral symmetry breaking scale, including, in Wilson's spirit, all operators of dimensionality less or equal to 6 which can be built with quark and chiral fields. The effect of the residual gluon interactions is contained in a number of coupling constants, whose running is studied. The resultin

Steven S. Gubser, Akikazu Hashimoto, Igor R. Klebanov, Michael Krasnitz

We investigate a version of fixed scalars for non-dilatonic branes which correspond to dilatations of the brane world-volume. We obtain a cross-section whose world-volume interpretation falls out naturally from an investigation of the breaking of conformal invariance by the irrelevant Born-Infeld corrections to Yang-Mills theory. From the same irrelevant wor

E. P. Esposito, I. A. Shovkovy, L. C. R. Wijewardhana

The finite temperature effective potential in the 2+1 dimensional Nambu-Jona-Lasinio model is constructed up to the next to leading order in the large $N$ expansion, where $N$ is the number of flavors in the model. The distinctive feature of the analysis is an inclusion of an additional scalar field, which allows us to circumvent the well known, and otherwis

Giancarlo Franzese, Antonio Coniglio

To understand the origin of the dynamical transition, between high temperature exponential relaxation and low temperature nonexponential relaxation, that occurs well above the static transition in glassy systems, a frustrated spin model, with and without disorder, is considered. The model has two phase transitions, the lower being a standard spin glass trans

H. Nordborg, G. Blatter

We present an extensive numerical study of vortex matter using the mapping to 2D bosons and Path-Integral Monte Carlo simulations. We find a first-order vortex lattice melting transition into an entangled vortex liquid. The jumps in entropy and density are consistent with experimental results on YBCO. The liquid is denser than the lattice and has a correlati

W. Peters, H. Lenske, U. Mosel

A relativistic and non-local model for the coherent photoproduction of pions on spin-zero nuclei is presented. The production operator is derived from an effective Lagrangian model that contains all the degrees of freedom known to contribute to the elementary process. Using the framework of DWIA, the matrix elements of this operator are evaluated using relat

Jose Caro

Stable recursive relations are presented for the numerical computation of the integrals $$\int d{\bf r}_1 d{\bf r}_2 r_1^{l-1} r_2^{m-1} r_{12}^{n-1} \exp{\{-αr_1 -βr_2 -γr_{12}\}}$$ ($l$, $m$ and $n$ integer, $α$, $β$ and $γ$ real) when the indices $l$, $m$ or $n$ are negative. Useful formulas are given for particular values of the parameters $α$, $β$ and $

C. Bourrely, F. Buccella, O. Pisanti, P. Santorelli

We perform a NLO analysis of polarized deep inelastic scattering data to test two different solutions to the so called spin crisis: one of them based on the axial gluon anomaly and consistent with the Bjorken sum rule and another one, where the defects in the spin sum rules and in the Gottfried sum rule are related. In this case a defect is also expected for

S. Chiku, T. Hatsuda

An optimized perturbation theory (OPT) at finite temperature T, which resums higher order terms in the naive perturbation, is developed in O(N) phi^4 theory. It is proved that (i) the renormalization of the ultra-violet divergences can be carried out systematically in any given order of OPT, and (ii) the Nambu-Goldstone theorem is fulfilled for arbitrary N a

Martin Lustig, Yoav Moriah

Non-isotopic Heegaard splittings of non-minimal genus were known previously only for very special 3-manifolds. We show in this paper that they are in fact a wide spread phenomenon in 3-manifold theory: We exhibit a large class of knots and manifolds obtained by Dehn surgery on these knots which admit such splittings. Many of the manifolds have irreducible He

Iain W. Stewart

The decays D^* -> Dπand D^* -> Dγare well described by heavy meson chiral perturbation theory. With the recent measurement of Br(D^{*+} -> D^+ γ), the D^{*0}, D^{*+}, and D_s^* branching fractions can be used to extract the D^*Dπand D^*Dγcouplings $g$ and $β$. The D^* -> Dγdecays receive important corrections at order $\sqrt{m_q}$ and, from the heavy quark m

Esther M. Hu, Lennox L. Cowie, Richard G. McMahon

We describe narrowband and spectroscopic searches for emission-line star forming galaxies in the redshift range 3 to 6 with the 10 m Keck II Telescope. These searches yield a substantial population of objects with only a single strong (equivalent width >> 100 Angstrom) emission line, lying in the 4000 - 10,000 Angstrom range. Spectra of the objects found in

Monica Borunda, M. Ruiz-Altaba

We compute the amount of inflation required to solve the horizon problem of cosmology in the pre-big-bang scenario. First we give a quick overview of string cosmology as developed by Veneziano and collaborators. Then we show that the amount of inflation in this background solves the horizon problem. We discuss fine-tuning.

Hoi-Kwong Lo, H. F. Chau

Quantum key distribution is widely thought to offer unconditional security in communication between two users. Unfortunately, a widely accepted proof of its security in the presence of source, device and channel noises has been missing. This long-standing problem is solved here by showing that, given fault-tolerant quantum computers, quantum key distribution

Pijushpani Bhattacharjee

It is pointed out that the observed extremely high energy cosmic rays (EHECR) above $10^{11}$ GeV and the observed baryon asymmetry of the Universe (BAU), both may have a common origin in baryon number violating decays of supermassive ``X'' particles released from cosmic topological defects (TDs) such as cosmic strings and monopoles. The X particles

Wen-Xiu MA

Two models of candidates for hereditary symmetry operators are proposed and thus many nonlinear systems of evolution equations possessing infinitely many commutative symmetries may be generated. Some concrete structures of hereditary symmetry operators are carefully analyzed on the base of the resulting general conditions and several corresponding nonlinear

J. Geiss, C. Greiner, E. L. Bratkovskaya, W. Cassing

We study the production of cc~ pairs in nuclear reactions at SPS energies within the covariant transport approach HSD. The production of cc~ is treated perturbatively employing experimental cross sections while the interactions of cc~ pairs with baryons are included by conventional cascade-type two-body collisions. Adopting 6 mb for the cc~-baryon cross sect

Valeriy N. Tolstoy

We construct two-parameter deformation of an universal enveloping algebra $U(g[u])$ of a polynomial loop algebra $g[u]$, where $g$ is a finite-dimensional complex simple Lie algebra (or superalgebra). This new quantum Hopf algebra called the Drinfeldian $D_{qη}(g)$ can be considered as a quantization of $U(g[u])$ in the direction of a classical r-matrix whic

Francesco Antonuccio, Oleg Lunin, Stephen S. Pinsky

We consider the dimensional reduction of N=1 {SYM}_{2+1} to 1+1 dimensions. The gauge groups we consider are U(N) and SU(N), where N is finite. We formulate the continuum bound state problem in the light-cone formalism, and show that any normalizable SU(N) bound state must be a superposition of an infinite number of Fock states. We also discuss how massless

P. Bowcock, M. Hayes, A. Taormina

The four fermionic currents of the affine superalgebra $sl(2/1)$ at fractional level $k=1/u-1$, u positive integer, are shown to be realised in terms of a free scalar field, an $sl(2)$ doublet field and a primary field of the parafermionic algebra $Z_{u-1}$.

M. Hayes, A. Taormina

The branching functions of the affine superalgebra $sl(2/1)$ characters into characters of the affine subalgebra $sl(2)$ are calculated for fractional levels $k=1/u-1$, u positive integer. They involve rational torus $A_{u(u-1)}$ and $Z_{u-1}$ parafermion characters.

F. Jegerlehner

We discuss a scenario of ``the path to physics at the Planck scale'' where todays theory of the interactions of elementary particles, the so called Standard Model (SM), emerges as a low energy effective theory describing the long distance properties of a sub--observable medium existing at the Planck scale, which we call ``ether''. Properties

R. Brustein, M. Gasperini, G. Veneziano

Cosmological perturbation equations derived from low-energy effective actions are shown to be invariant under a duality transformation reminiscent of electric-magnetic, strong-weak coupling, S-duality. A manifestly duality-invariant approximation for perturbations far outside the horizon is introduced, and it is argued to be useful even during a high curvatu

M. I. Caicedo, A. Restuccia

$BF$ theories defined over non trivial line bundles are studied. It is shown that such theories describe a realization of a non trivial higher order bundle. The partition function differs from the usual one -in terms of the Ray Singer Torsion- by a factor that arises from the non triviality of the line bundles.

Seiji Terashima, Sung-Kil Yang

We propose Seiberg-Witten geometry for N=2 gauge theory with gauge group $E_6$ with massive $N_f$ fundamental hypermultiplets. The relevant manifold is described as a fibration of the ALE space of $E_6$ type. It is observed that the fibering data over the base ${\bf CP}^1$ has an intricate dependence on hypermultiplet bare masses.

C. M. Maekawa, M. R. Robilotta

The scalar-isoscalar field of an effective chiral Lagrangian transforms differently in either linear or non-linear frameworks: in the former case it is the counterpart of the pion whereas in the latter it is chiral invariant on its own. We compare the predictions from these two models for nucleon interactions and find results which are identical for two-body

P. J. Mulders

In this talk I want to illustrate the many possibilities for studying the structure of hadrons in hard scattering processes by giving a number of examples involving increasing complexity in the demands for particle polarization, particle identification or polarimetry. In particular the single spin asymmetries will be discussed. The measurements discussed in

H. Hamidian, K. Huitu, K. Puolamaki, D. -X. Zhang

By considering the constraints from nucleon decay we obtain upper limits on tan beta in generalized supersymmetric SU(5) grand unified theories with gauge-mediated supersymmetry breaking. We find that the predicted values of tan beta in these models are mostly inconsistent with the constraints from nucleon decay.

C. Boros, Liang Zuo-tang

Longitudinal polarization of Lambda produced in $e^+e^-$ annihilation at LEP energies is calculated in a picture for the spin content of Lambda which is consistent with the polarized deep inelastic lepton-nucleon scattering data and SU(3) flavor symmetry for hyperon decay so that the spin of Lambda is not completely carried by its $s$-valence quark. A compar

R Delbourgo, Dongsheng Liu

We give best covariant amplitude decompositions for two-body decay processes involving ground state hadrons ($0^-, 1^-, {1/2}^+, {3/2}^+$) and show how these are simply related to helicity amplitudes. After discussing how electromagnetic interactions are incorporated via meson dominance in a relativistic supermultiplet scheme, we extend the analysis to weak

R. Sekhar Chivukula

Discovering the dynamics responsible for electroweak symmetry breaking is the outstanding question facing particle physics today, and the answer will be found in the next decade. In these lectures I discuss the range of models which have been proposed to explain electroweak symmetry breaking. I begin with an overview of Higgs models, with emphasis on the nat

D0 collaboration, B. Abbott

The results of a search for W boson pair production in pbar-p collisions at sqrt{s}=1.8 TeV with subsequent decay to emu, ee, and mumu channels are presented. Five candidate events are observed with an expected background of 3.1+-0.4 events for an integrated luminosity of approximately 97 pb^{-1}. Limits on the anomalous couplings are obtained from a maximum

D0 Collaboration, B. Abbott et al

The shape of the transverse momentum distribution of W bosons (p_T(W)) produced in pbarp collisions at sqrt(s)= 1.8 TeV is measured with the DO detector at Fermilab. The result is compared to QCD perturbative and resummation calculations over the p_T(W) range from 0-200 GeV/c. The shape of the distribution is consistent with the theoretical prediction.

D. V. Ahluwalia, C. Burgard

The interplay of gravitation and the quantum-mechanical principle of linear superposition induces a new set of neutrino oscillation phases. These ensure that the flavor-oscillation clocks, inherent in the phenomenon of neutrino oscillations, redshift precisely as required by Einstein's theory of gravitation. The physical observability of these phases in

A. Garcia, F. W. Hehl, C. Laemmerzahl, A. Macias

We consider a (non--Riemannian) metric--affine gravity theory, in particular its nonmetricity--torsion sector ``isomorphic'' to the Einstein--Maxwell theory. We map certain Einstein--Maxwell electrovacuum solutions to it, namely the Plebański--Demiański class of Petrov type D metrics.

Gonzalo Usaj, Horacio M. Pastawski, Patricia R. Levstein

The NMR technique allows one to create a non-equilibrium local polarization and to detect its later evolution. By a change of the sign of the effective dipolar Hamiltonian, the apparently diffusive dynamics is reverted, generating a polarization echo (PE). This echo attenuates as a function of the time $t_R$ elapsed until the dynamics is reverted. We report

E. Ben-Naim, P. L. Krapivsky

We study domain distributions in the one-dimensional Ising model subject to zero-temperature Glauber and Kawasaki dynamics. The survival probability of a domain, $S(t)\sim t^{-ψ}$, and an unreacted domain, $Q_1(t)\sim t^{-δ}$, are characterized by two independent nontrivial exponents. We develop an independent interval approximation that provides close estim

F. Woynarovich, P. Forgacs

The scaling limit of the less than half filled attractive Hubbard chain is studied. This is a continuum limit in which the particle number per lattice site, n, is kept finite (0<n<1) while adjusting the interaction and bandwidth in a such way that there is a finite mass gap. We construct this limit both for the spectrum and the secular equations describing t

T. P. C. van Noije, M. H. Ernst

We study the single particle velocity distribution for a granular fluid of inelastic hard spheres or disks, using the Enskog-Boltzmann equation, both for the homogeneous cooling of a freely evolving system and for the stationary state of a uniformly heated system, and explicitly calculate the fourth cumulant of the distribution. For the undriven case, our re

M. -C. Bellissent-Funel

Previous studies of the structure of liquid water under pressure performed by neutron diffraction, allowed us to establish two structural limits in liquid water. These two limits are closely connected to the two known forms of amorphous ice : the low density amorphous ice (LDA) and the high density amorphous ice (HDA). In the present paper, we propose some i

R. Aguado, G. Platero

Using a time dependent selfconsistent model for vertical sequential tunneling,we study the appearance of charge instabilities that lead to the formation of electric field domains in a weakly coupled doped superlattice in the presence of high magnetic fields parallel to the transport direction. The interplay between the high non linearity of the system --comi

A. N. Korotkov

The operation of resistively-coupled single-electron transistor (R-SET) is studied quantitatively. Due to the Nyquist noise of the coupling resistance, degradation of the R-SET performance is considerable at temperatures $T$ as small as $10^{-3} e^2/C$ (where $C$ is the junction capacitance) while the voltage gain becomes impossible at $T\agt 10^{-2}e^2/C$.

V. Kravchenko, N. Minina, A. Savin, C. B. Sorensen

Resistance, magnetoresistance and their temperature dependencies have been investigated in the 2D hole gas at a [001] p-GaAs/Al$_{0.5}$Ga$_{0.5}$As heterointerface under [110] uniaxial compression. Analysis performed in the frame of hole-hole scattering between carriers in the two spin splitted subbands of the ground heavy hole state indicates, that h-h scat

G. Benfatto, G. Gentile, V. Mastropietro

We consider the static Holstein model, describing a chain of Fermions interacting with a classical phonon field, when the interaction is weak and the density is a rational number. We show that the energy of the system, as a function of the phonon field, has two stationary points, defined up to a lattice translation, which are local minima in the space of fie

Patrick Gagliardini, Stephan Haas, T. M. Rice

We apply a generalized version of the Lieb-Schultz-Mattis Theorem to fermionic ladder systems to show the existence of a low-lying excited state (except for some special fillings). This can be regarded as a non-perturbative proof for the conservation under interaction of the sum of the Fermi wave vectors of the individual channels, corresponding to a general

A. A. Aligia, E. Gagliano, Liliana Arrachea, K. Hallberg

We consider a generalized Hubbard model with on-site and nearest-neighbour repulsions U and V respectively, and nearest-neighbour hopping for spin up (down) which depends on the total occupation n_b of spin down (up) electrons on both sites involved. The hopping parameters are t_{AA}, t_{AB} and t_{BB} for n_b=0,1,2 respectively. We briefly summarize results

Debashish Chowdhury

The phenomenon of immunological memory has been known for a long time. But, the underlying mechanism is poorly understood. According to the theory of clonal selection the response to a specific invading antigen (e.g., bacteria) is offered by a specific clone of the cells. Some of the lymphocytes activated during the primary response remain dormant and keep c

Kazuhiro Kuboki, Manfred Sigrist

Recently a phenomenological Ginzburg-Landau (GL) theory has been proposed to describe the occurrence of a locally time-reversal symmetry (T) breaking state near a Josephson junction between unconventional superconductors. In this paper we derive this type of GL free energy microscopically from the t-J model within a slave-boson mean-field approximation. The

M. Fogelstrom, S. -K. Yip

In this paper we study the order parameter and density of states near a grain boundary between two $d_{x^2-y^2}$ superconductors. We examine broken time reversal symmetry near the interface. In particular we show that, under suitable circumstances, time reversal symmetry must be broken even when the order parameter is purely $d_{x^2-y^2}$ everywhere in space

B. Schmittmann, R. K. P. Zia

Based on a high temperature expansion, we compute the two-point correlation function and the critical line of an Ising lattice gas driven into a non-equilibrium steady state by a uniform bias E. The lowest nontrivial order already reproduces the key features, i.e., the discontinuity singularity of the structure factor and the (qualitative) E-dependence of th

Raphael Zarum, Sarben Sarkar

Von Neumann entropy production rates of the quantised kicked rotor interacting with an environment are calculated. A significant correspondence is found between the entropy contours of the classical and quantised systems. This is a quantative tool for describing quantum-classical correspondence in the transition to chaos.

Antonio Politi, Alessandro Torcini, Stefano Lepri

A conjecture connecting Lyapunov exponents of coupled map lattices and the node theorem is presented. It is based on the analogy between the linear stability analysis of extended chaotic states and the Schrödinger problem for a particle in a disordered potential. As a consequence, we propose an alternative method to compute the Lyapunov spectrum. The implica

Pijushpani Bhattacharjee

The topological defect scenario of origin of the observed highest energy cosmic rays is reviewed. Under a variety of circumstances, topological defects formed in the early Universe can be sources of very massive particles in the Universe today. The decay products of these massive particles may be responsible for the observed highest energy cosmic ray particl

F. A. Jenet, S. B. Anderson, V. M. Kaspi, T. A. Prince

We present a total of 48 minutes of observations of the nearby, bright millisecond pulsar PSR J0437-4715 taken at the Parkes radio observatory in Australia. The data were obtained at a central radio frequency of 1380 MHz using a high-speed tape recorder that permitted coherent Nyquist sampling of 50 MHz of bandwidth in each of two polarizations. Using the hi

J. D. Monnier, T. R. Geballe, W. C. Danchi

New multi-epoch, mid-infrared (8-13 microns) spectrophotometric observations are presented for 30~late-type stars. The observations were collected over a four year period (1994-1997), permitting an investigation of the mid-infrared spectral shape as a function of the pulsation cycle (typically 1-2 years). The spectra of stars with little excess infrared emis

V. M. Kaspi

We summarize the current observational evidence for associations between supernova remnants and neutron stars, including radio pulsars, proposed &#34;inactive&#34; young neutron stars, &#34;anomalous&#34; X-ray pulsars, and soft gamma-ray repeaters, and argue that the paradigm that all young neutron stars are Crab-like requires reconsideration.

V. M. Kaspi, R. A. Remillard

RXTE/ASM observations of PSR B1259-63 near the 1997 periastron passage find no emission brighter than appximately 10 times that detected by ASCA during the 1994 periastron encounter, demonstrating that the pulsar is unlikely to have undergone even brief episodes of accretion.

S. R. Kulkarni, M. H. van Kerkwijk

RX J0720.4-3125 is an unidentified bright soft X-ray source which shows pulsations at a 8.39 s period and has a thermal spectrum. We present deep B and R band images of its X-ray localization. We find one possible counterpart in the X-ray error box, with magnitudes B=26.6+/-0.2 and R=26.9+/-0.3. The very high X-ray to optical flux ratio confirms that this ob

Chris Simpson

We undertake a quantitative investigation, using Monte Carlo simulations, of the amount by which quasars are expected to exceed radio galaxies in optical luminosity in the context of the `receding torus&#39; model. We compare these simulations with the known behaviour of the [O III] 5007 and [O II] 3727 emission lines and conclude that [O III] is the better

D. J. Fixsen, E. Dwek, J. C. Mather, C. L. Bennett

The COBE FIRAS data contain foreground emission from interplanetary, Galactic interstellar dust and extragalactic background emission. We use three different methods to separate the various emission components, and derive the spectrum of the extragalactic Far InfraRed Background (FIRB). Each method relies on a different set of assumptions, which affect the F

J. Bagchi, V. Pislar, G. B. Lima Neto

We report the first detection of an inverse Compton X-ray emission, spatially correlated with a very steep spectrum radio source (VSSRS), 0038-096, without any detected optical counterpart, in cluster Abell 85. The ROSAT PSPC data and its multiscale wavelet analysis reveal a large scale (linear diameter of the order of 500 h^{-1}_{50} kpc), diffuse X-ray com

Wil J. M. van Breugel, S. A. Stanford, Hyron Spinrad, Daniel Stern

We present deep near-IR images of high redshift radio galaxies obtained with NIRC on the Keck I telescope. In most cases, the near-IR data sample rest wavelengths at ~4000 Angstroms, free of strong emission lines. At z > 3, the rest frame optical morphologies generally have faint, large-scale emission surrounding multiple components of ~10 kpc size. The brig

Eric C. Ford, Michiel van der Klis, Philip Kaaret

In observations with the Rossi X-ray Timing Explorer we have discovered quasi-periodic oscillations (QPOs) near 1 kHz from 4U 1705-44, a low--mass X-ray binary with a neutron star classified as an atoll source. In six separate observations, we detect one QPO with a frequency ranging between 770 and 870 Hz and a 4% rms fraction in the full detector energy ban

Mark Lacy, Steve Rawlings, Katherine M. Blundell, Susan E. Ridgway

Multi-wavelength imaging and spectroscopy of the z=0.708 radio galaxy 3C441 and a red aligned optical/infrared component are used to show that the most striking aspect of the radio-optical ``alignment effect&#39;&#39; in this object is due to the interaction of the radio jet with a companion galaxy in the same group or cluster. The stellar population of the

R. J. Garcia Lopez, M. R. Perez de Taoro

The Be II 3131 A doublet has been observed in the solar-type stars 16 Cyg A & B and in the late G-type star rho 1 Cnc, to derive their beryllium abundances. 16 Cyg A & B show similar (solar) beryllium abundances while 16 Cyg B, which has been proposed to have a planetary companion of ~2 M_Jup, is known to be depleted in lithium by a factor larger than 6 with

M. Feroci, L. A. Antonelli, M. Guainazzi, J. M. Muller

The BeppoSAX satellite has recently opened a new way towards the solution of the long standing gamma-ray bursts&#39; (GRBs) enigma, providing accurate coordinates few hours after the event thus allowing for multiwavelength follow-up observational campaigns. The BeppoSAX Narrow Field Instruments observed the region of sky containing GRB970111 16 hours after t

Yoshiaki Sofue

The rotation curve of the small-mass starburst galaxy M82 has a steep nuclear rise, peaking at 200 pc radius, and then, declines in a Keplerian fashion. This rotation curve mimics that for a central bulge of spiral galaxies with high concentration of stellar mass. The declining rotation indicates that its extended disk mass is missing. In order to explain th

Antoinette Songaila

Metal line ratios in a sample of 13 quasar spectra obtained with the HIRES spectrograph on the KeckI telescope have been analyzed to characterize the evolution of the metagalactic ionizing flux near a redshift of 3. The evolution of SiIV/CIV has been determined using three different techniques: using total column densities of absorption line complexes, as in

Hideki Asada

We discuss how inhomogeneities of the universe affect observations of the gravitational lensing; (1) the bending angle, (2) the lensing statistics and (3) the time delay. In order to take account of the inhomogeneities, the Dyer-Roeder distance is used, which includes a parameter representing the clumpiness of the matter along the line of sight. It is shown

Shu Kawaguchi, Atsushi Moriwaki

In this paper, we will consider a generalization of Bogomolov&#39;s inequality and Cornalba-Harris-Bost&#39;s inequality to semistable families of arithmetic varieties under the idea that geometric semistability implies a certain kind of arithmetic positivity. The first one is an arithmetic analogue of the relative Bogomolov&#39;s inequality proved by the se

A. Lawrence, N. Nekrasov, C. Vafa

Extending recent work of Kachru and Silverstein, we consider ``orbifolds&#39;&#39; of 4-dimensional $\mathcal{N}=4$ SU(n) super-Yang-Mills theories with respect to discrete subgroups of the SU(4) $R$-symmetry which act nontrivially on the gauge group. We show that for every discrete subgroup of SU(4) there is a canonical choice of imbedding of the discrete g

G. Steigman, I. Tkachev

We obtain restrictions on the universal baryon fraction, f_B = Omega_B/Omega_0, by assuming that the observed microlensing events towards the Large Magellanic Cloud are due to baryonic MACHOs in the halo of the Galaxy and by extracting a bound to the total mass of the Milky Way from the motion of tracer galaxies in the Local Group. We find a lower bound f_B

J. F. Gunion

I review extended Higgs sectors and constraints thereon arising from $ρ=1$, gauge-coupling unification and $b\to s\gam$. The couplings and decays of the Higgs boson eigenstates are outlined for triplet representations. Direct experimental probes of exotic Higgs bosons are reviewed with a focus on the important role that would be played by an $e^-e^-$ or $μ^-

B. Carter, R. A. Battye

The classical linearised gravitational self interaction of a Goto-Nambu string is examined in four spacetime dimensions. Using a conveniently gauge independent tensorial treatment, the divergent part of the self-force is shown to be exactly zero. This is due to cancelation by a contribution that was neglected in the previous treatments. This result has impli

Steven Abel, Carlos Savoy

We make a critical reappraisal of `unbounded-from-below&#39; (UFB) constraints in the MSSM and R-parity violating models. We explain why the `traditional&#39; UFB bounds are neither necessary nor sufficient and propose, instead, a sufficient condition which ensures that there are no local minima along the flat directions. This conservative (but meaningful) c

Xinwei Kong, Finn Ravndal

At energies much less than the electron mass $m$ the effects of quantum fluctuations in the vacuum due to virtual electron loops can be included by extending the Maxwell Lagrangian by additional non-renormalizable terms corresponding to the Uehling and Euler-Heisenberg interactions. This effective field theory is used to calculate the properties of the QED v

S. de Brion, F. Ciorcas, G. Chouteau, P. Lejay

The magnetic phase diagram of $La_{1-δ}MnO_{3}$ powdered samples have been studied as a function of $δ$ in the low doping range. $La_{0.97}MnO_{3}$ has a canted magnetic structure at low temperature $(θ\simeq 130\QTR{group}{{}^{\circ}})$. Above $T_{C}=118K$, it becomes a paramagnet with a huge effective magnetic moment, $μ_{eff}=6.0μ_{B}$, reflecting the pre

K. Reuter, J. A. Vamvakas, D. K. Saldin, V. Blum

Following on the success of the recent application of holographic LEED to the determination of the 3D atomic geometry of Si adatoms on a SiC(111) p(3x3) surface, which enabled that structure to be solved, we show in this paper that a similar technique allows the direct recovery of the local geometry of adsorbates forming superstructures as small as p(2x2), e

S. V. Zenkin

The index theorem is employed to extend the no-go theorem for lattice chiral Dirac fermions to translation non-invariant and non-local formulations.

Toru Sakai

The ground state magnetization process of the S=1 antiferromagnetic chain with the easy-axis single-ion anisotropy described by negative $D$ is investigated. It is numerically found that a phase transition between two different gapless phases occurs at an intermediate magnetic field between the starting and saturation points of the magnetization for $-1.49<D

Andreas Aste, G&#34;unter Scharf

We show for the case of interacting massless vector bosons, how the structure of Yang-Mills theories emerges automatically from a more fundamental concept, namely perturbative quantum gauge invariance. It turns out that the coupling in a non-abelian gauge theory is necessarily of Yang-Mills type plus divergence- and coboundary couplings. The extension of the

Gabriela Barenboim, Nuria Rius

We study the finite-temperature effective potential of minimal left-right symmetric models containing a bidoublet and two triplets in the scalar sector. We perform a numerical analysis of the parameter space compatible with the requirement that baryon asymmetry is not washed out by sphaleron processes after the electroweak phase transition. We find that the

B. A. Ivanov, A. K. Kolezhuk, V. E. Kireev

We consider a domain wall in the mesoscopic quasi-one-dimensional sample (wire or stripe) of weakly anisotropic two-sublattice antiferromagnet, and estimate the probability of tunneling between two domain wall states with different chirality. Topological effects forbid tunneling for the systems with half-integer spin S of magnetic atoms which consist of odd

Marek Cieplak, Malte Henkel, Jan Karbowski, Jayanth R. Banavar

The master equation for 12-monomer lattice heteropolymers is solved numerically and the time evolution of the occupancy of the native state is determined. At low temperatures, the median folding time follows the Arrhenius law and is governed by the longest relaxation time. For good folders, significant kinetic traps appear in the folding funnel whereas for b

V. B. Belyaev, D. E. Monakhov, D. V. Naumov, F. M. Penkov

We evaluate the effect of screening by bound electron in the 7Be + p --> 8B + photon reaction, where 7Be target contains bound electron, in the framework of the adiabatic representation of the three particle problem. A comparison with two other approximations (united atom and folding) is presented. A good agreement between the ``united atom&#39;&#39; approxi

Guy Bonneau

We analyse in a systematic way the (non-)compact four dimensional Einstein-Weyl spaces equipped with a Bianchi metric. We show that Einstein-Weyl structures with a Class A Bianchi metric have a conformal scalar curvature of constant sign on the manifold. Moreover, we prove that most of them are conformally Einstein or conformally Kähler ; in the non-exact Ei

Franco Ferrari, Ignazio Lazzizzera

In recent times some interesting field theoretical descriptions of the statistical mechanics of entangling polymers have been proposed by various authors. In these approaches, a single test polymer fluctuating in a background of static polymers or in a lattice of obstacles is considered. The extension to the case in which the configurations of two or more po

S. B. Dubovichenko

An exponential version of a deep nucleon-nucleon potential involving forbidden states and a tensor component is proposed. The parameters of interaction are chosen by fitting the low-energy characteristics and phase shifts of np scattering at energies up to 500 MeV. Such potential have not node in D wave as against earlier proposed.

S. M. Nishigaki, P. H. Damgaard, T. Wettig

We derive the hole probability and the distribution of the smallest eigenvalue of chiral hermitian random matrices corresponding to Dirac operators coupled to massive quarks in QCD. They are expressed in terms of the QCD partition function in the mesoscopic regime. Their universality is explicitly related to that of the microscopic massive Bessel kernel.

L. Y. Gorelik, N. I. Lundin, V. S. Shumeiko, R. I. Shekhter

The dynamics of a superconducting quantum point contact biased at subgap voltages is shown to be strongly affected by a microwave electromagnetic field. Interference among a sequence of temporally localized, microwave-induced Landau-Zener transitions between current carrying Andreev levels results in energy absorption and in an increase of the subgap current

Kentaro Urasaki, Tetsuro Saso

We study the two-band Hubbard model introduced by Fu and Doniach as a model for FeSi which is suggested to be a Kondo insulator. Using the self-consistent second-order perturbation theory combined with the local approximation which becomes exact in the limit of infinite dimensions, we calculate the specific heat, the spin susceptibility and the dynamical con

Shigeyoshi Mori, Isao Harada, Takashi Tonegawa

Dynamic spin correlation function of the $S=1/2$ antiferromagnetic spin chain with alternating nearest neighbor and competing next nearest neighbor interactions is studied using the numerical diagonalization method. We find characteristics of the correlation function, which are the consequence of the dimer order in the ground state: (1) A typical singlet-tri

V. D. Ivashchuk, S. -W. Kim, V. N. Melnikov

A subclass of recently discovered class of solutions in multidimensional gravity with intersecting p-branes related to Lie algebras and governed by a set of harmonic functions is considered. This subclass in case of three Euclidean p-branes (one electric and two magnetic) contains a cosmological-type solution (in 11-dimensional model with two 4-forms) relate

Tetsuo Deguchi, Ruihong Yue, Koichi Kusakabe

We discuss the ground state and some excited states of the half-filled Hubbard model defined on an open chain with L sites, where only one of the boundary sites has a different value of chemical potential. We consider the case when the boundary site has a negative chemical potential -p and the Hubbard coupling U is positive. By an analytic method we show tha

N. E. Mavromatos, D. V. Nanopoulos, I. Samaras, K. Zioutas

We present the main properties of ferroelectricity, with emphasis given to a specific family of hydrated ferroelectric crystals, which can serve as model systems for corresponding configurations in biology like the microtubules. An experimental method is described, which allows to establish the ferroelectric property of microtubules in suspension.