4,154 research outputs found
Born-Infeld Corrections to the Entropy Function of Heterotic Black Holes
We use the black hole entropy function to study the effect of Born-Infeld
terms on the entropy of extremal black holes in heterotic string theory in four
dimensions. We find that after adding a set of higher curvature terms to the
effective action, attractor mechanism works and Born-Infeld terms contribute to
the stretching of near horizon geometry. In the alpha'--> 0 limit, the
solutions of attractor equations for moduli fields and the resulting entropy,
are in conformity with the ones for standard two charge black holes.Comment: 17 pages;v2:minor changes,added ref
Non-Supersymmetric Attractors in BI black holes
We study attractor mechanism in extremal black holes of Einstein-Born-Infeld
theories in four dimensions. We look for solutions which are regular near the
horizon and show that they exist and enjoy the attractor behavior. The
attractor point is determined by extremization of the effective potential at
the horizon. This analysis includes the backreaction and supports the validity
of non-supersymmetric attractors in the presence of higher derivative
interactions in the gauge field part.Comment: 15 pages, minor corrections, references adde
Equilibration, generalized equipartition, and diffusion in dynamical Lorentz gases
We prove approach to thermal equilibrium for the fully Hamiltonian dynamics
of a dynamical Lorentz gas, by which we mean an ensemble of particles moving
through a -dimensional array of fixed soft scatterers that each possess an
internal harmonic or anharmonic degree of freedom to which moving particles
locally couple. We establish that the momentum distribution of the moving
particles approaches a Maxwell-Boltzmann distribution at a certain temperature
, provided that they are initially fast and the scatterers are in a
sufficiently energetic but otherwise arbitrary stationary state of their free
dynamics--they need not be in a state of thermal equilibrium. The temperature
to which the particles equilibrate obeys a generalized equipartition
relation, in which the associated thermal energy is equal to
an appropriately defined average of the scatterers' kinetic energy. In the
equilibrated state, particle motion is diffusive
Generic chiral superfield model on nonanticommutative N=1/2 superspace
We consider the generic nonanticommutative model of chiral-antichiral
superfields on superspace. The model is formulated in
terms of an arbitrary K\"ahlerian potential, chiral and antichiral
superpotentials and can include the nonanticommutative supersymmetric
sigma-model as a partial case. We study a component structure of the model and
derive the component Lagrangian in an explicit form with all auxiliary fields
contributions. We show that the infinite series in the classical action for
generic nonanticommutative model of chiral-antichiral superfields in D=4
dimensions can be resumed in a compact expression which can be written as a
deformation of standard Zumino's lagrangian and chiral superpotential. Problem
of eliminating the auxiliary fields in the generic model is discussed and the
first perturbative correction to the effective scalar potential is obtained.Comment: 12 pages, LaTeX; text revised and extended, references adde
Non-stationary de Sitter cosmological models
In this note it is proposed a class of non-stationary de Sitter, rotating and
non-rotating, solutions of Einstein's field equations with a cosmological term
of variable function.Comment: 11 pages, Latex. International Journal of Modern Physics D (accepted
for publication
Last scattering, relic gravitons and the circular polarization of the CMB
The tensor contribution to the -mode polarization induced by a magnetized
plasma at last scattering vanishes exactly. Conversely a polarized background
of relic gravitons cannot generate a -mode polarization. The reported
results suggest that, in the magnetized CDM paradigm, the dominant
source of circular dichroism stems from the large-scale fluctuations of the
spatial curvature.Comment: 8 pages, no figure
Dynamics of electromagnetic waves in Kerr geometry
Here we are interested to study the spin-1 particle i.e., electro-magnetic
wave in curved space-time, say around black hole. After separating the
equations into radial and angular parts, writing them according to the black
hole geometry, say, Kerr black hole we solve them analytically. Finally we
produce complete solution of the spin-1 particles around a rotating black hole
namely in Kerr geometry. Obviously there is coupling between spin of the
electro-magnetic wave and that of black hole when particles propagate in that
space-time. So the solution will be depending on that coupling strength. This
solution may be useful to study different other problems where the analytical
results are needed. Also the results may be useful in some astrophysical
contexts.Comment: 15 Latex pages, 4 Figures; Accepted for publication in Classical and
Quantum Gravit
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