September 1996 arXiv papers — page 15

T. Rauscher, F. -K. Thielemann, K. -L. Kratz

Nuclear Astrophysics requires the knowledge of reaction rates over a wide range of nuclei and temperatures. In recent calculations the nuclear level density - as an important ingredient to the statistical model (Hauser-Feshbach) - has shown the highest uncertainties. In a back-shifted Fermi-gas formalism utilizing an energy-dependent level density parameter

Silvia Mollerach, Esteban Roulet

Due to the large kick velocities with which neutron stars are born in supernovae explosions, their spatial distribution is more extended than that of their progenitor stars. The large scale height of the neutron stars above the disk plane makes them potential candidates for microlensing of stars in the Large Magellanic Cloud. Adopting for the distribution of

S. Talon, J. -P. Zahn

We examine the role of anisotropic turbulence on the shear instabilities in a stratified flow. Such turbulence is expected to occur in the radiative interiors of stars, due to their differential rotation and their strong stratification, and the turbulent transport associated with it will be much stronger in the horizontal than in the vertical direction. It w

Keisuke Taniguchi, Takashi Nakamura

The innermost stable circular orbits (ISCO) of coalescing neutron star-black hole binary are studied taking into account both the tidal and relativistic effects. We adopt the generalized pseudo-Newtonian potential to mimic the general relativistic effects of gravitation. It is found that the separation of the neutron star and the black hole at the ISCO is gr

J. I. Katz

The phenomenon called the ``sub-Sun'' is the specular reflection of sunlight by horizontally oriented plates of ice. Although well-known in meteorological optics, the hydrodynamics of the orientation is not quantitatively understood. I review the theory of torques on objects at low Reynolds numbers, define coefficients $C_o$, $C_p$, and $C_ψ$ which d

Jeffrey A. Harvey, Gregory Moore

We define an algebra on the space of BPS states in theories with extended supersymmetry. We show that the algebra of perturbative BPS states in toroidal compactification of the heterotic string is closely related to a generalized Kac-Moody algebra. We use D-brane theory to compare the formulation of RR-charged BPS algebras in type II compactification with th

J. Blümlein, S. Riemersma, W. L. van Neerven, A. Vogt

The differences are discussed between various next-to-leading order prescriptions for the QCD evolution of parton densities and structure functions. Their quantitative impact is understood to an accuracy of 0.02\%. The uncertainties due to the freedom to choose the renormalization and factorization scales are studied. The quantitative consequences of the dif

Sergei V. Ketov

Taking the (2,2) strings as a starting point, we discuss the equivalent integrable field theories and analyze their symmetry structure in 2+2 dimensions from the viewpoint of string/membrane unification. Requiring the Lorentz invariance and supersymmetry in the (2,2) string target space leads to an extension of the (2,2) string theory to a theory of 2+2 dime

G. J. Galloway, E. Woolgar

For any asymptotically flat spacetime with a suitable causal structure obeying (a weak form of) Penrose's cosmic censorship conjecture and satisfying conditions guaranteeing focusing of complete null geodesics, we prove that active topological censorship holds. We do not assume global hyperbolicity, and therefore make no use of Cauchy surfaces and their

Viqar Husain

An unusual four-dimensional generally covariant and supersymmetric SU(2) gauge theory is described. The theory has propagating degrees of freedom, and is invariant under a local (left-handed) chiral supersymmetry, which is half the supersymmetry of supergravity. The Hamiltonian 3+1 decomposition of the theory reveals the remarkable feature that the local sup

Ahmed Hindawi, Burt A. Ovrut, Daniel Waldram

We use the four-dimensional N=2 central charge superspace to give a geometrical construction of the Abelian vector-tensor multiplet consisting, under N=1 supersymmetry, of one vector and one linear multiplet. We derive the component field supersymmetry and central charge transformations, and show that there is a super-Lagrangian, the higher components of whi

Anindya K. Biswas

In this paper we analyze the earlier constructions of the type IIA dual pairs through orientifolding. By an appropriate choice of $Γ$-matrix basis for the spinor representations of the $U$-duality group, we give an explicit relationship between the orientifold models and their dual pairs.

P. Kanti, K. Tamvakis

We consider the combined Yang Mills-Dilaton-Gravity system in the presence of a Gauss-Bonnet term as it appears in the $4D$ Effective Superstring Action. We give analytical arguments and demonstrate numerically the existence of black hole solutions with non-trivial dilaton and Yang Mills hair for the particular case of SU(2) gauge fields. The thermodynamical

N. N. Achasov, A. A. Kozhevnikov

The results of an analysis are presented of some recent data on the reactions $e^+e^-\toπ^+π^-π^+π^-$, $e^+e^-\toπ^+π^-π^0π^0$ with the subtracted $ωπ^0$ events, $e^+e^-\toωπ^0$, $e^+e^-\toηπ^+π^-$, $e^+e^-\toπ^+π^-$, $K^-p\toπ^+π^-Λ$, the decays $J/ψ\toπ^+π^-π^0$, $tau^-\toν_tauπ^+π^-π^-π^0$ $tau^-\toν_τωπ^-$, upon taking into account both the strong energy

M. Beneke

I briefly review three topics of recent interest concerning power corrections, renormalons and Sudakov resummation: (a) $1/Q$ corrections to event shape observables in $e^+ e^-$ annihilation, (b) power corrections in Drell-Yan production and (c) factorial divergences that arise in resummation of large infrared (Sudakov) logarithms in moment or `real' spa

M. Beneke

We discuss the calculation of the width difference $ΔΓ_{B_s}$ between the $B_s$ mass eigenstates to next-to-leading order in the heavy quark expansion. $1/m_b$-corrections are estimated to reduce the leading order result by typically $30\%$. The error of the present estimate $(ΔΓ/Γ)_{B_s} = 0.16^{+0.11}_{-0.09}$ could be substantially improved by pinning dow

Peter Filip

In the paper we investigate a possibility to perform shape-sensitive HBT analysis in transversal plane. We study presently used Side-Out decomposition of the correlation function and we do not find it to be very sensitive for the detection of a shape of source distribution in transversal plane. Therefore we suggest to use X-Y decomposition of the correlation

Jorge Pullin

Contents: APS Topical Group in Gravitation News: April 1997 Joint APS/AAPT Meeting Research briefs: GEO600 by Karsten Danzmann Black hole microstates in string theory by Gary Horowitz LIGO project status by Stan Whitcomb The Hamiltonian constraint of quantum gravity and loops by John Baez Conference reports: International conference on gravitational waves by

D. J. Litman

Cue phrases may be used in a discourse sense to explicitly signal discourse structure, but also in a sentential sense to convey semantic rather than structural information. Correctly classifying cue phrases as discourse or sentential is critical in natural language processing systems that exploit discourse structure, e.g., for performing tasks such as anapho

A. Gerevini, L. Schubert

We propose some domain-independent techniques for bringing well-founded partial-order planners closer to practicality. The first two techniques are aimed at improving search control while keeping overhead costs low. One is based on a simple adjustment to the default A* heuristic used by UCPOP to select plans for refinement. The other is based on preferring `

C. Rascon, L. Mederos, G. Navascues

The first well founded perturbation theory for classical solid systems is presented. Theoretical approaches to thermodynamic and structural properties of the hard-sphere solid provide us with the reference system. The traditional difficulties of all previous approaches are overcome. The perturbation is a first order term in an expansion of the Helmholtz free