May 1997 arXiv papers — page 12

Andreas Wacker, Antti-Pekka Jauho, Stefan Zeuner, S. James Allen

We report a combined theoretical and experimental study of electrical transport in weakly-coupled doped superlattices. Our calculations exhibit negative differential conductivity at sufficiently high electric fields for all dopings. In low-doped samples the presence of impurity bands modifies the current-voltage characteristics substantially and we find two

I. V. Volovich

The second quantization of M(atrix) theory in the free (Boltzmannian) Fock space is considered. It provides a possible framework to the recent Susskind proposal that U(N) supersymmetic Yang-Mills theories for all N might be embedded in a single dynamical system. The second quantization of M(atrix) theory can also be useful for the study of the Lorentz symmet

Igor Bandos, Paolo Pasti, Dmitri Sorokin, Mario Tonin

We review a generic structure of conventional (Nambu-Goto and Dirac-Born-Infeld-like) worldvolume actions for the superbranes and show how it is connected through a generalized action construction with a doubly supersymmetric geometrical approach to the description of super-p-brane dynamics as embedding world supersurfaces into target superspaces.

M. Maul, A. Schafer, P. Indelicato

In this paper we present some concepts in heavy ion atomic physics for the extraction of parity violating effects. We investigate the effects of the so-called Stark-quenching, i.e., the fast decay of a meta stable state induced by a Stark field, and the superposition of one- and two-photon transitions in beryllium-like heavy ions. It turns out that the discu

D. N. Tripathy, Subodha Mishra

Considering the fact that the present universe might have been formed out of a system of ficticious self-gravitating particles, fermionic in nature, each of mass $m$, we are able to obtain a compact expression for the radius $R_0$ of the universe by using a model density distribution $ρ(r)$ for the particles which is singular at the origin. This singularity

P. C. Tandy

We review recent progress in modeling the quark-gluon content of mesons and their low-energy interactions through the Global Color Model field theory. An emphasis is placed on techniques that are shared with the approach based on truncations of the Dyson-Schwinger equations of QCD. In contrast to most other field theory models for QCD degrees of freedom in h

Eric Babson, Anders Björner, Svante Linusson, John Shareshian

Complexes of (not) connected graphs, hypergraphs and their homology appear in the construction of knot invariants given by V. Vassiliev. In this paper we study the complexes of not $i$-connected $k$-hypergraphs on $n$ vertices. We show that the complex of not $2$-connected graphs has the homotopy type of a wedge of $(n-2)!$ spheres of dimension $2n-5$. This

John Brodie

We derive four dimensional gauge theories with exceptional groups $F_4$, $E_8$, $E_7$, and $E_7$ with matter, by starting from the duality between the heterotic string on $K3$ and F-theory on a elliptically fibered Calabi-Yau 3-fold. This configuration is compactified to four dimensions on a torus, and by employing toric geometry, we compute the type IIB mir

I. Ya. Aref'eva

We discuss classical composite p-brane solutions and their quantization using the conjecture that their fluctuations may be described via degrees of freedom of Dirichlet strings ended on these p-branes. We work with Dirichlet (super)strings in framework of string field theory for open (super)strings. To elaborate in this scheme the eleventh dimension modes w

Youngjai Kiem, Chang-Yeong Lee, Dahl Park

We consider the type IIB supergravity in ten dimensions compactified on S^1 \times T^4, with intersecting one and five D-branes in the compact dimensions. By imposing the spherical symmetry in the resulting five dimensional theory, we further reduce the s-wave sector of the theory to a two dimensional dilaton gravity. Via this construction, the techniques de

H. Lotter

The low $x$ limit of deep inelastic electron proton scattering is considered using methods of perturbative QCD. In the first part we investigate the phenomenological consequences of the resummation of leading logarithms in $1/x$ given by the BFKL pomeron. We apply the BFKL pomeron to the inclusive structure function $F_2$, to the diffractive production of ve

G. Altarelli, G. F. Giudice, M. L. Mangano

An excess of events at large Q2 with a positron in the final state has been observed at HERA which, if confirmed, would be a signal of new physics. It is not clear at present if a signal of comparable rate is also seen in the charged current channel (with an antineutrino in the final state). In this note we analyse the implications of the presence of such a

Romuald A. Janik, Maciej A. Nowak, Gabor Papp, Ismail Zahed

We motivate and use the concept of free random variables for the studies of the de-pinning transition of flux lines in superconductors as recently discussed by Hatano and Nelson. We derive analytical conditions for the critical points of the eigenvalue distribution in the complex plane for all values of the transverse magnetic field in one-dimension, in agre

L. A. N. Amaral, K. B. Lauritsen

We investigate sandpile models where the updating of unstable columns is done according to a stochastic rule. We examine the effect of introducing nonlocal relaxation mechanisms. We find that the models self-organize into critical states that belong to three different universality classes. The models with local relaxation rules belong to a known universality

Thierry Giamarchi, Pierre Le Doussal

We examine here various aspects of the statics and dynamics of disordered elastic systems such as manifolds and periodic systems. Although these objects look very similar and indeed share some underlying physics, periodic systems constitute a class of their own with markedly different properties. We focus on such systems, review the methods allowing to treat

Daniel A. Dale, Riccardo Giovanelli, Martha P. Haynes, Marco Scodeggio

We present first results of an all-sky observing program designed to improve the quality of the I band Tully-Fisher (TF) template and to obtain the reflex motion of the Local Group with respect to clusters to z = 0.06. We are obtaining between 5 and 15 TF measurements per cluster on a sample of 50 clusters at intermediate redshifts (0.02 < z < 0.06). Present

James B. Hartle

Quantum mechanics for matter fields moving in an evaporating black hole spacetime is formulated in fully four-dimensional form according to the principles of generalized quantum theory. The resulting quantum theory cannot be expressed in a 3+1 form in terms of a state evolving unitarily or by reduction through a foliating family of spacelike surfaces. That i

Donald Marolf

The horizon area and curvature of three-charge BPS black strings are studied in the D-brane ensemble for the stationary black string. The charge distributions along the string are used to translate the classical expressions for the horizon area and curvature of BPS black strings with waves into operators on the D-brane Hilbert space. Despite the fact that an

Yu Shi

This paper has been withdrawn, and will be superseded by another submission.

Daniel L. Miller

In the present work we study the two-point correlation function $R(ε)$ of the quantum mechanical spectrum of a classically chaotic system. Recently this quantity has been computed for chaotic and for disordered systems using periodic orbit theory and field theory. In this work we present an independent derivation, which is based on periodic orbit theory. The

Sukanta Bose, Sayan Kar

We present analytic cosmological solutions in a model of two-dimensional dilaton gravity with back reaction. One of these solutions exhibits a graceful exit from the inflationary to the FRW phase and is nonsingular everywhere. A duality related second solution is found to exist only in the ``pre-big-bang'' epoch and is singular at $\tau = 0$. In either case

Ruediger Schack

We show that the quantum baker&#39;s map, a prototypical map invented for theoretical studies of quantum chaos, has a very simple realization in terms of quantum gates. Chaos in the quantum baker&#39;s map could be investigated experimentally on a quantum computer based on only 3 qubits.

Sabir M. Gusein-Zade, Igancio Luengo, Alejandro Melle-Hernández

For a germ of a meromorphic function f=P/Q, we offer notions of the monodromy operators at zero and at infinity. If the holomorphic functions P and Q are non-degenerated with respect to their Newton diagrams, we give an analogue of the formula of Varchenko for the zeta-functions of these monodromy operators.

Sayan Kar

We show, using purely classical considerations and logical extrapolation of results belonging to point particle theories, that the metric background field in which a string propagates must satisfy an Einstein or an Einstein-like equation. Additionally, there emerge restrictions on the worldsheet curvature, which seems to act as a source for spacetime gravity

M. Beneke, I. Z. Rothstein, Mark B. Wise

In this letter we address issues involved in quarkonium production near the boundaries of phase space. It is shown that higher-order non-perturbative contributions are enhanced in this kinematic region and lead to a breakdown of the non-relativistic (NRQCD) expansion. This breakdown is a consequence of sensitivity to the kinematics of soft gluon radiation an

S. Vargas-Castrillon

The possibility of symmetry non-restoration at high temperature is explored in a strongly interacting Higgs system described by an effective Chiral Lagrangian. Despite a na\&#34;ıve perturbative hint of symmetry non-restoration when the temperature is increased, non-perturbative methods point towards symmetry restoration. (Contribution to the XXXIInd Rencont

Junegone Chay, Sun Myong Kim

We consider the azimuthal correlation of the final-state particles in charged weak-current processes. This correlation provides a test of perturbative quantum chromodynamics. The azimuthal asymmetry is large in the semi-inclusive processes in which we identify a final-state hadron, say, a charged pion compared to that in the inclusive processes in which we d

T. W. Baumgarte, G. B. Cook, M. A. Scheel, S. L. Shapiro

We analyze the stability of relativistic, quasi-equilibrium binary neutron stars in synchronous circular orbit. We explore stability against radial collapse to black holes prior to merger, and against orbital plunge. We apply theorems based on turning points along uniformly rotating sequences of constant angular momentum and rest mass to locate the onset of

Thomas Thiemann

We extend the recently developed kinematical framework for diffeomorphism invariant theories of connections for compact gauge groups to the case of a diffeomorphism invariant quantum field theory which includes besides connections also fermions and Higgs fields. This framework is appropriate for coupling matter to quantum gravity. The presence of diffeomorph

T. Thiemann

We quantize the generators of the little subgroup of the asymptotic Poincaré group of Lorentzian four-dimensional canonical quantum gravity in the continuum. In particular, the resulting ADM energy operator is densely defined on an appropriate Hilbert space, symmetric and essentially self-adjoint. Moreover, we prove a quantum analogue of the classical positi

Thomas Thiemann

It is an old speculation in physics that, once the gravitational field is successfully quantized, it should serve as the natural regulator of infrared and ultraviolet singularities that plague quantum field theories in a background metric. We demonstrate that this idea is implemented in a precise sense within the framework of four-dimensional canonical Loren

Thomas Thiemann

The quantization of Lorentzian or Euclidean 2+1 gravity by canonical methods is a well-studied problem. However, the constraints of 2+1 gravity are those of a topological field theory and therefore resemble very little those of the corresponding Lorentzian 3+1 constraints. In this paper we canonically quantize Euclidean 2+1 gravity for arbitrary genus of the

Thomas Thiemann

This paper deals with several technical issues of non-perturbative four-dimensional Lorentzian canonical quantum gravity in the continuum that arose in connection with the recently constructed Wheeler-DeWitt quantum constraint operator. 1) The Wheeler-DeWitt constraint mixes the previously discussed diffeomorphism superselection sectors which thus become spu

N. Nakamura, Y. Suzumura

We examine the spectral function of the single electron Green function at finite temperatures for the Tomonaga-Luttinger model which consists of the mutual interaction with only the forward scattering. The spectral weight, which is calculated as a function of the frequency with the fixed wave number, shows that several peaks originating in the excitation spe

E. Vesperini, D. C. Heggie

In this paper we show the results of a large set of N-body simulations modelling the evolution of globular clusters driven by relaxation,stellar evolution,disk shocking and including the effects of the tidal field of the Galaxy. We investigate the evolution of multi-mass models with a power-law initial mass function (IMF) starting with different initial mass

L. Armus, G. Neugebauer, M. D. Lehnert, K. Matthews

Near-infrared images of the luminous, high redshift (z=2.1108) radio loud quasar 4C+09.17 reveal a complex structure. The quasar (K=15.76 mag) is surrounded by three &#34;companion&#34; objects having 17.9< K < 20.2 mag at radii of 1.7&#34; < r < 2.9&#34;, as well as bright, diffuse emission. The brightest companion has a redshift of z=0.8384 (Lehnert & Beck

Nadya Shirokova

In this paper we develop the theory of finite-type invariants for homologically nontrivial 3-manifolds. We construct an infinite-dimensional affine space with a hypersurface in it corresponding to manifolds with Morse singularities. Connected components of the complement of this hypersurface correspond to homeomorphism type of spin 3-manifolds. This suggests

Herve M. Carruzzo, Clare C. Yu

Vortex lattices in the high temperature superconductors undergo a first order phase transition which has thus far been regarded as melting from a solid to a liquid. We point out an alternative possibility of a two step process in which there is a first order transition from an ordinary vortex lattice to a soft vortex solid followed by another first order mel

T. B. Liverpool, R. Golestanian, K. Kremer

We study the statistical mechanics of double-stranded semi-flexible polymers using both analytical techniques and simulation. We find a transition at some finite temperature, from a type of short range order to a fundamentally different sort of short range order. In the high temperature regime, the 2-point correlation functions of the object are identical to

Esteban Calzetta, Mariana Grana

We consider the influence of mode - mode coupling in the inflaton field on the spectrum of primordial fluctuations. To this end, we formulate a phenomenological model where the inflaton fluctuations are treated as a fluid undergoing turbulent motion. Under suitable assumptions, it is possible to estimate the size and scale of fluctuations in velocity, which

Sharmanthie Fernando, Freydoon Mansouri

We obtain a class of rotating charged stationary circularly symmetric solutions of Einstein-Maxwell theory coupled to a topological mass term for the Maxwell field. These solutions are regular, have finite mass and angular momentum, and are asymptotic to the uncharged extreme BTZ black hole.

Bogdan Bucicovschi

The purpose of this note is to extend the results of V. Guillemin on elliptic self-adjoint pseudodifferential operators of order one, from operators defined on smooth functions on a closed manifold to operators defined on smooth sections in a vector bundle of Hilbert modules of finite type over a finite von Neumann algebra.

N. Armesto, A. Capella

We present a quantitative description of $J/ψ$ and $ψ^\prime$ suppression in proton-nucleus and nucleus-nucleus collisions at CERN energies. We use a conventional hadronic framework based on nuclear absorption plus final state interaction of the $J/ψ$ or $ψ^\prime$ with co-moving hadrons.

Dongsu Bak, Hyunsoo Min

The radiation reaction of a BPS monopole in the presence of incident electromagnetic waves as well as massless Higgs waves is analyzed classically. The reactive forces are compared to those of $W$ boson that is interpreted as a dual partner of the BPS monopole. It is shown that the damping of acceleration is dual to each other, while in the case of finite si

P. H. Song, Doochul Kim

We investigate the localization of two interacting particles in one-dimensional random potential. Our definition of the two-particle localization length, $ξ$, is the same as that of v. Oppen et al. [Phys. Rev. Lett. 76, 491 (1996)] and $ξ$&#39;s for chains of finite lengths are calculated numerically using the recursive Green&#39;s function method for severa

J. Maharana, H. Singh

The ten-dimensional type IIA string effective action with cosmological constant term is dimensionally reduced on a d-dimensional torus to derive lower dimensional effective action. The symmetries of the reduced effective action are examined. It is shown that the resulting six-dimensional theory does not remain invariant under $SO(4,4)$ symmetry whereas the r

Roberto Onofrio, Lorenza Viola

The Lindblad approach to open quantum systems is introduced for studying the dynamics of a single trapped ion prepared in nonclassical motional states and subjected to continuous measurement of its internal population. This results in an inhibition of the dynamics similar to the one occurring in the quantum Zeno effect. In particular, modifications to the Ja

Dmitry Tamarkin

An &#39;isomorphism&#39; between the &#39;moduli space&#39; of star products on $\R^2$ and the &#39;moduli space&#39; of all formal Poisson structures on $\R^2$ is established.

F. Gagel

A rational expansion of the Fermi density operator is proposed. This approach allows to calculate efficiently physical properties of fermionic systems at finite temperatures without solving an eigenvalue problem. Using N evaluations of the Green&#39;s function, the Fermi density operator can be approximated, subject to a given precision, in the energy interv

J. Dobes

Within the context of the isovector-pairing SO(5) model, three methods measuring numbers of different kinds of nucleon pairs are discussed. Though methods do not give the same results, the odd-even staggering in pair numbers in even-even and odd-odd N=Z nuclei and the reduction of the np pair number with increasing T_z is observed in all three procedures.

Robert E. Gompf

We show that a homotopy equivalence between manifolds induces a correspondence between their spin^c-structures, even in the presence of 2-torsion. This is proved by generalizing spin^c-structures to Poincare complexes. A procedure is given for explicitly computing the correspondence under reasonable hypotheses.

Arjun Berera

I will discuss hadron-hadron collisions where the final state is kinematically of the kind associated with double-pomeron-exchange (DPE) and has large transverse momentum jets. I will show that in addition to the conventional factorized (FDPE) contribution, there is a non-factorized (NDPE) contribution which has no pomeron beam jet. Results of calculations f

J. F. Gunion

I review the ability of the LHC (large hadron collider), NLC (next linear lepton collider) and FMC (first muon collider) to detect and study Higgs bosons, with emphasis on the Higgs bosons of extended Higgs sectors, especially those of the minimal supersymmetric standard model (MSSM). Particular attention is given to means for distinguishing the lightest neu

T. Fugleberg, I. Halperin, A. Zhitnitsky

We discuss a two dimensional SU(N) Yang-Mills theory coupled to massive adjoint fermions for different worlds classified by the integer k=0,1,...N-1. We study the fermion condensate for these unconnected worlds as a function of the parameter k. We show that the condensate as well as the spectrum of the theory do depend on this vacuum parameter k. Technically

Erasmo Ferreira, Flávio Pereira

Accounting for the two independent correlation functions of the QCD vacuum, we improve the simple and consistent description given by the model of the stochastic vacuum to the high-energy pp and pbar-p data, with a new determination of parameters of non-perturbative QCD. The increase of the hadronic radii with the energy accounts for the energy dependence of

Zhang Chen

We discuss the general operator product expansion of a non-forward unequal mass virtual compton scattering scattering amplitude. We find that the expansion now should be done in double moments with new moment variables. There are in the expansion new sets of leading twist operators which have overall derivatives, and they mix under renormalization. We comput

Erasmo Ferreira, Flávio Pereira

The functional dependence of the high-energy observables of total cross section and slope parameter on the sizes of the colliding hadrons predicted by the model of the stochastic vacuum and the corresponding relations used in the geometric model of Povh and Hüfner are confronted with the experimental data. The existence of a universal term in the expression

U. Aglietti

This is a written version of two lectures given at the First School on Field Theory and Gravitation in Vitoria (Brasil) April 15-19, 1997. We discuss the foundation of QCD as the theory of strong interactions and the perturbative analysis of e^+e^- annihilation into hadrons. Typical concepts of perturbative QCD studies, such as collinear singularities, jets,

J. C. Collins

This talk covers a selection of topics that were discussed at this meeting in the non-heavy-ion sessions: (a) The high $Q^{2}$ events at HERA and their theoretical interpretation. (b) The issues of how well we know the predictions of QCD, with a particular emphasis on resummation. (c) Anomalies in jet production in association with $W$ bosons at the Tevatron

F. M. Renard, S. Spagnolo, C. Verzegnassi

We analyze, in a rather general model where anomalous triple gauge couplings are present, the visible effects in R$_b$ (measured at LEP1), in W pair production (to be measured at LEP2) and in the muon anomalous magnetic moment (to be measured at BNL). From the combination of the three experiments a remarkable improvement on the pure LEP2 constraints is obtai

Paul Hoyer, D. P. Roy

Using an intrinsic parton model we estimate the rough shape and size of the intrinsic gluon component of the nucleon, corresponding to an energy scale $Q$ of the order $\lqcd$. It is nearly as hard in shape as the valence quark, while its size accounts for a quarter of the nucleon momentum. Both are in qualitative agreement with the input leading twist gluon

Yoshiharu Kawamura, Tatsuo Kobayashi, Manabu Watanabe

We give a generic method to select a realistic $μ$-term generation mechanism based on the radiative electroweak symmetry breaking scenario and study which type is hopeful within the framework of string theory. We discuss effects of the moduli F-term condensation and D-term contribution to soft scalar masses.

Vicente Azcoiti, Giuseppe Di Carlo, Angelo Galante, Aurelio Grillo

We analyze the phase diagram of compact QED on the torus with a chirally symmetric four fermion interaction added to the usual Wilson action. Inside a mean field approximation for the four fermion term, a line of first order phase transitions and another one of second order are found in the $(β, G)$ plane. Approaching the second order line a continuum limit

Chris Michael, Janne Peisa

We discuss methods to obtain accurate hadronic spectra with propagating quarks. Comparing the determination of masses for spin-exotic hybrid mesons with glueball mass determinations, we conclude that quark propagators from all sites to all other sites would enable great improvement in the errors. Such propagators are achievable by using stochastic estimators

Tim Bolton

A method is described for estimating muon track momentum from the distribution of hits along tracks in dense calorimeters due to multiple Coulomb scattering (MCS). The method requires only well-aligned conventional drift chambers or similar tracking devices and can be implemented with or without a magnetic field present. Neutrino experiments can use this tec

Gungwon Kang

We have shown that, as in the case of black holes, an ergosphere itself with no event horizon inside can evaporate spontaneously, giving energy radiation to spatial infinity until the ergoregion disappears. However, the feature of his quantum ergoregion instability is very much different from black hole radiation. It is rather analogous to a laser amplificat

N. Fowler, I. Raeburn

A product system E over a semigroup P is a family of Hilbert spaces {E_s:s\in P} together with multiplications E_s \times E_t\to E_{st}. We view E as a unitary- valued cocycle on P, and consider twisted crossed products A \times_{β,E} P involving E and an action βof P by endomorphisms of a C*-algebra A. When P is quasi-lattice ordered in the sense of Nica, w

A. V. Balatsky, S. A. Trugman

We argue that any superconductor with magnetic impurities is gapless due to a Lifshitz tail in the density of states extending to zero energy. At low energy the density of states $ν(E \to 0)$ remains finite. We show that fluctuations in the impurity distribution produce regions of suppressed superconductivity, which are responsible for the low energy density

M. A. Korotin, V. I. Anisimov, D. I. Khomskii, G. A. Sawatzky

Band structure calculations of CrO2 carried out in the LSDA+U approach reveal a clear picture of the physics behind the metallic ferromagnetic properties. Arguments are presented that the metallic ferromagnetic oxide CrO2 belongs to a class of materials in which magnetic ordering exists due to double exchange (in this respect CrO2 turns out to be similar to

R. Friedberg, H. C. Ren, O. Tchernyshyov

In a recent paper [A.S.Alexandrov, J.Phys.:Condens.Matter 8, 6923 (1996); cond-mat/9603111], it has been suggested that there is no Cooper pairing in boson-fermion models of superconductivity. We show that this conjecture is based on an inconsistent approximation that violates an exact identity. Quite generally, the divergence of the fermion t-matrix (the Th

Walter Zimmermann, Raymond Fresard, Peter Woelfle

The spin and charge structure factors are calculated for the Hubbard model on the square lattice near half-filling using a spin-rotation invariant six-slave boson representation. The charge structure factor shows a broad maximum at the zone corner and is found to decrease monotonically with increasing interaction strength and electron density and increasing

Rama Cont, Marc Potters, Jean-Philippe Bouchaud

The concepts of scale invariance, self-similarity and scaling have been fruitfully applied to the study of price fluctuations in financial markets. After a brief review of the properties of stable Levy distributions and their applications to market data we indicate the shortcomings of such models and describe the truncated Levy flight as an alternative model

M. Campostrini, A. Pelissetto, P. Rossi, E. Vicari

In three-dimensional O(N) models, we investigate the low-momentum behavior of the two-point Green&#39;s function G(x) in the critical region of the symmetric phase. We consider physical systems whose criticality is characterized by a rotational-invariant fixed point. Several approaches are exploited, such as strong-coupling expansion of lattice non-linear O(

G. Varelogiannis, E. N. Economou

We examine the effect on the DC resistivity of small-q electron-phonon scattering, in a system with the electronic topology of the high-T_c oxides. Despite the fact that the scattering is dominantly forward, its contribution to the transport can be significant due to ``ondulations&#39;&#39; of the bands in the flat region and to the umpklapp process. When th

Tooru Taniguchi

We give a method of describing thermodynamical transport phenomena, based on a quantum scattering theoretical approach. We consider a quantum system of particles connected to thermodynamical reservoirs by leads. The effects of the reservoirs are imposed as an asymptotic condition at the end of the leads. We derive an expression for a current of a conserved q

Pierre Emmanuel Berche, Bertrand Berche

We investigate the surface critical behavior of two-dimensional multilayered aperiodic Ising models in the extreme anisotropic limit. The system under consideration is obtained by piling up two types of layers with respectively $p$ and $q$ spin rows coupled via nearest neighbor interactions $λr$ and $λ$, where the succession of layers follows an aperiodic se

Mauro M. Doria, Flavio M. R. d&#39;Almeida, O. Buisson

A plasma wave propagates inside an anisotropic superconducting film sandwiched between two semi-infinite non-conducting bounding dieletric media. Along the c-axis, perpendicular to the film surfaces, an external magnetic field is applied. We show how vortices, known to cause dissipation and change the penetration depth, affect the propagative mode. We obtain

Steven H. Simon, Nigel R. Cooper

Recently, Tieke et al (to be published in PRL) have observed the relation S_{yx} = alpha B dS_{xx}/dB for the components of the thermopower tensor in the quantum Hall regime, where alpha is a constant and B is the magnetic field. Simon and Halperin (PRL 73, 3278 (1994)) have suggested that an analogous relation observed for the resistivity tensor R_{xx} = αB

A. J. Roberts

Consider briefly the equations of fluid dynamics-they describe the enormous wealth of detail in all the interacting physical elements of a fluid flow-whereas in applications we want to deal with a description of just that which is interesting. In a wide variety of situations, simple approximate models are needed to perform practical simulations and make fore

France Allard, Peter H. Hauschildt

In this paper, we review the current theory of very low mass stars model atmospheres including the coolest known M~dwarfs, M~subdwarfs, and brown dwarfs, i.e. T$_{eff} \leq 5,000 $K and $-2.0 \le [M/H] \le +0.0$. We discuss ongoing efforts to incorporate molecular and grain opacities in cool stellar spectra, as well as the latest progress in deriving the eff

C. D. Dermer, J. G. Skibo

Two different model-independent mapping techniques have been applied to OSSE, SMM, TGRS and balloon data and reveal a feature in the 0.511 MeV electron-positron annihilation radiation pattern of our galaxy centered roughly at l=-2 deg. and b=10 deg. with a flux of 5x10^(-4) 0.511 MeV ph/cm^2/s. If near the galactic center, then positron sources are producing

Diego F. Torres, Héctor Vucetich, A. Plastino

Within an early Universe scenario, nonextensive thermostatistics (NET) is investigated on the basis of data concerning primordial Helium abundance. We obtain first order corrections to the energy densities and weak interactions rates, and use them to compute the deviation in the primordial Helium abundance. After compare with observational results, a severe

Rohan Mahadevan, Eliot Quataert

We investigate the form of the momentum distribution function for protons and electrons in an advection-dominated accretion flow (ADAF). We show that for all accretion rates, Coulomb collisions are too inefficient to thermalize the protons. The proton distribution function is therefore determined by the viscous heating mechanism, which is unknown. The electr

Helio J. Rocha-Pinto, Walter J. Maciel

We address the question of the occurrence of star formation bursts in the solar neighbourhood by using the metallicity distribution of the G dwarfs. We present a method to recover the star formation history using simultaneously the metallicity distribution and the age-metallicity relation. The method associates the number of stars in a given metallicity inte

Gilles Chabrier, Dominique Méra

We use recent low-mass star models, which reproduce accurately the observed sequences of various globular clusters, to convert the observed luminosity functions into bolometric luminosity functions and mass functions down to the bottom of the main sequence. These mass functions are well describedby a slowly rising power-law $dN/dm\propto m^{-α}$, with $0.5\w

Ronald A. Remillard, Edward H. Morgan, Jeffrey E. McClintock, Charles D. Bailyn

The two galactic `microquasars&#39; with superluminal radio jets have been quite active during 1996, generatinga variety of studies involving both NASA and ground-based observatories. GRS~1915+105 has displayed dramatic accretion instability in observations with RXTE, revealing X-ray light curves and emission states unlike anything previously seen. Variable

Peter H. Hauschildt, France Allard, David R. Alexander, E. Baron

We present detailed NLTE Ti~I calculations in model atmospheres of cool dwarf and giant stars. A fully self-consistent NLTE treatment for a Ti~I model atom with 395 levels and 5279 primary bound-bound transitions is included, and we discuss the implication of departures from LTE in this atom for the strengths of Ti~I lines and TiO molecular bands in cool sta

Gilles Chabrier

We summarize recent improvements in model atmosphere and internal structure of faint white dwarfs. We derive an analytical cooling theory which illustrates the effects of various physical processes on the energy budget and the cooling history of cool white dwarfs. We consider in particular the effect of chemical fractionation at crystallization. This process

Mario Vietri

Gamma-ray bursts are produced by the dissipation of the kinetic energy of a highly relativistic fireball, via the formation of a collisionless shock. When this happens, Ultra High Energy Cosmic Rays up to 10^20 eV are produced. I show in this paper that these particles produce, via synchrotron emission as they cross the acceleration region, photons up to 300

R. Tantalo, A. Bressan, C. Chiosi

The line strength indices Hb, Mg2, and <Fe>, together with their gradients and dependence on the galaxy luminosity (mass), observed in elliptical galaxies are customarily considered as reliable indicators of systematic differences in age and abundances of Mg and Fe. In this paper, we address the question whether or not the indices Mg2 and <Fe> (and their gra

Gilles Chabrier, Isabelle Baraffe

We present a review of the most recent improvements in the theory of low-mass star-like objects, in the stellar and sub-stellar domains. Comparison is made with various recent observations.

A. Cavaliere, N. Menci, P. Tozzi

We model the effects of shocks on the diffuse, X-ray emitting baryons in clusters of galaxies. Shocks separate the infalling from the inner gas nearly at equilibrium, and dominate the compression and the density gradients of the latter in the dark-matter potential of the cluster. We find that, independently of the detailed shape of the potential, the density

K. Shimasaku, M. Fukugita

(Abridged) A simple quantitative model is presented for the history of galaxies to explain galaxy number counts, redshift distributions and some other related observations. We first infer that irregular galaxies and the disks of spiral galaxies are young, probably formed at $z\approx 0.5-2$ from a simultaneous consideration of colours and gas content under a

Carlos De Breuck, Wil van Breugel, Huub Rottgering, George Miley

We have started a search for High Redshift Radio Galaxies (HZRGs) in an area covering 7 sr by selecting a sample of Ultra Steep Spectrum (USS) sources with a low flux density cut-off S(1400 MHz) > 10 mJy and a steep spectral index cut-off of alpha < -1.3 (S ~ nu**alpha) from the WENSS, NVSS and TEXAS surveys. Our first results for 27 sources show that we are

Massimiliano Mella

A Mukai variety is a Fano n-fold of index n-2. In this paper we study the fundamental divisor of a Mukai variety with at worst log terminal singularities. The main result is a complete classification of log terminal Mukai varieties which have not good divisors, examples of &#34;bad&#34; varieties are given. In such a way we also give a shorter proof of Mukai

Alexander Degtyarev

A new invariant, the Pontrjagin-Viro form, of algebraic surfaces is introduced and studied. It is related to various Rokhlin-Guillou-Marin forms and generalizes Mikhalkin&#39;s complex separation. The form is calculated for all real Enriques surfaces for which it is well defined.

Michael Dine, Nathan Seiberg

We study the leading irrelevant operators along the flat directions of certain supersymmetric theories. In particular, we focus on finite N=2 (including N=4) supersymmetric field theories in four dimensions and show that these operators are completely determined by the symmetries of the problem. This shows that they are generated only at one loop and are not

Brett Ellman, Louis Taillefer

We report on the a.c. magnetic response of superconducting UPt_3 in a d.c. magnetic field. At low fields (H < H^*), the in-phase susceptibility shows a sharp drop at $T_c$ followed by a gradual decrease with decreasing temperature, while the out-of-phase component shows a large peak at T_c followed by an unusual broad peak. As the B-C phase line is crossed (

John K. Elwood, Nikolaos Irges, Pierre Ramond

We present a model for the observed hierarchies among the Yukawa couplings of the standard model in the context of an effective low energy theory with an anomalous U(1) symmetry. This symmetry, a generic feature of superstring compactification, is a remnant of the Green-Schwarz anomaly cancellation mechanism. The gauge group is that of the standard model, au

Dongsheng Du, Hongying Jin, Yadong Yang

With respect to large samples of $B_c$ mesons expected to be produced at CERN Large Hadron Collider(LHC) and the large branching ratios $Br(B_{c}\to τ\barν)$ and $Br(B_{c}\to μ\barν)$, we suggest that $B_c$ purely leptonic decays could offer an unique probe of the standard model and its extensions such as two Higgs doublet models and models involving supersy