864 research outputs found
Closed strings in Ramond-Ramond backgrounds
We write the IIB Green-Schwarz action in certain general classes of curved
backgrounds threaded with Ramond-Ramond fluxes. The fixing of the kappa
symmetry in the light-cone gauge and the use of supergravity Bianchi identities
simplify the task. We find an expression that truncates to quartic order in the
spacetime spinors and relays interesting information about the vacuum structure
of the worldsheet theory. The results are particularly useful in exploring
integrable string dynamics in the context of the holographic duality.Comment: 24 pages; this is a significant revision to hep-th/0112063 with new
results added, and including comparison with recent literature; v2: minor
typos corrected, citations adde
Branes wrapping black holes as a purely gravitational dielectric effect
In this paper we give a microscopical description of certain configurations
of branes wrapping black hole horizons in terms of dielectric gravitational
waves. Interestingly, the configurations are stable only due to the
gravitational background. Therefore, this constitutes a nice example of purely
gravitational dielectric effect.Comment: 17 pages, no figures. JHEP published versio
Bivariate Hermite Interpolation and Numerical Curves
AbstractIn this paper, Hermite interpolation by bivariate algebraic polynomials of total degree ⩽nis considered. The interpolation parameters are the values of a function and its partial derivatives up to some ordernν−1 at the nodeszν=(xν, yν),ν=1, …, s, wherenνis the multiplicity ofzν. The sequence N={n1, …, ns; n} of multiplicities associated with the degree of interpolating polynomials is investigated. Some results of the paper were announced in [GHS93]
Gravitational Radiation from Pulsating White Dwarfs
Rotating white dwarfs undergoing quasi-radial oscillations can emit
gravitational radiation in a frequency range from 0.1 - 0.3 Hz. Assuming that
the energy source for the gravitational radiation comes from the oblateness of
the white dwarf induced by the rotation, the strain amplitude is found to be
\sim 10^{-27} for a white dwarf at \sim 50 pc. The galactic population of these
sources is estimated to be \sim 10^7, and may produce a confusion limited
foreground for proposed advanced detectors in the frequency band between
space-based and ground-based interferometers. Nearby oscillating white dwarfs
may provide a clear enough signal to investigate white dwarf interiors through
gravitational wave asteroseismology.Comment: Accepted for Astrophysical Journal Letters. Changed value of
branching ratio resulting in an order of magnitude drop in gravitational wave
amplitude
Generally Covariant Actions for Multiple D-branes
We develop a formalism that allows us to write actions for multiple D-branes
with manifest general covariance. While the matrix coordinates of the D-branes
have a complicated transformation law under coordinate transformations, we find
that these may be promoted to (redundant) matrix fields on the transverse space
with a simple covariant transformation law. Using these fields, we define a
covariant distribution function (a matrix generalization of the delta function
which describes the location of a single brane). The final actions take the
form of an integral over the curved space of a scalar single-trace action built
from the covariant matrix fields, tensors involving the metric, and the
covariant distribution function. For diagonal matrices, the integral localizes
to the positions of the individual branes, giving N copies of the single-brane
action.Comment: 34 pages, LaTeX. v2: comments and refs adde
Nuclear symmetry energy effects on neutron stars properties
We construct a class of nuclear equations of state based on a schematic
potential model, that originates from the work of Prakash et. al.
\cite{Prakash-88}, which reproduce the results of most microscopic
calculations. The equations of state are used as input for solving the
Tolman-Oppenheimer-Volkov equations for corresponding neutron stars. The
potential part contribution of the symmetry energy to the total energy is
parameterized in a generalized form both for low and high values of the baryon
density. Special attention is devoted to the construction of the symmetry
energy in order to reproduce the results of most microscopic calculations of
dense nuclear matter. The obtained nuclear equations of state are applied for
the systematic study of the global properties of a neutron star (masses, radii
and composition). The calculated masses and radii of the neutron stars are
plotted as a function of the potential part parameters of the symmetry energy.
A linear relation between these parameters, the radius and the maximum mass of
the neutron star is obtained. In addition, a linear relation between the radius
and the derivative of the symmetry energy near the saturation density is found.
We also address on the problem of the existence of correlation between the
pressure near the saturation density and the radius.Comment: 17 pages, 25 figure
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