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

Observation of Resonant Diffusive Radiation in Random Multilayered Systems

Diffusive Radiation is a new type of radiation predicted to occur in randomly inhomogeneous media due to the multiple scattering of pseudophotons. This theoretical effect is now observed experimentally. The radiation is generated by the passage of electrons of energy 200KeV-2.2MeV through a random stack of films in the visible light region. The radiation intensity increases resonantly provided the Cherenkov condition is satisfied for the average dielectric constant of the medium. The observed angular dependence and electron resonance energy are in agreement with the theoretical predictions. These observations open a road to application of diffusive radiation in particle detection, astrophysics, soft X-ray generation and etc.. `Comment: 4pages, 4figure

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