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

Stability of naked singularities and algebraically special modes

We show that algebraically special modes lead to the instability of naked singularity spacetimes with negative mass. Four-dimensional negative-mass Schwarzschild and Schwarzschild-de Sitter spacetimes are unstable. Stability of the Schwarzschild-anti-de Sitter spacetime depends on boundary conditions. We briefly discuss the generalization of these results to charged and rotating singularities.Comment: 6 pages. ReVTeX4. v2: Minor improvements and extended discussion on boundary conditions. Version to appear in Phys. Rev.

Global liquidity and financial flows to developing countries: new trends in emerging markets and their implications

This paper attempts to examine: (i) the factors responsible for this revival and surge in capital flows into developing countries; (ii) the qualitative changes in financial integration that are accompanying this surge; and (iii) the impact that this surge is having on financial volatility and vulnerability, macroeconomic management and growth, in countries that have been “successful” in attracting such flows. It argues that in the wake of financial liberalization that facilitates cross-border flows of capital, supply-side factors rather than the financing requirements of developing countries, explain the surge. Financial liberalization and the globalization of finance, have also resulted in changes in the financial structure – the markets, institutions and instruments that define the global financial architecture – that are increasing risk and financial fragility. Associated with this increasing risk, are changes in the business practices and motivations of financial firms that reduce the role of finance in ensuring broad-based economic growth.

Magnetoresistance of single-domain ferromagnetic particles

We have performed magnetoresistance measurements on single-domain, submicron elliptical Ni particles using nonmagnetic probes in a four probe geometry at liquid helium temperatures. In the smallest particles, the magnetoresistance shows sharp jumps which are associated with the switching of individual domains. Using an anisotropic magnetoresistance model, we can reconstruct hysteresis loops of the normalized magnetization. The remanent magnetization in zero applied magnetic field is typically 15 percent less than the saturation magnetization. This relaxation of the magnetization may be due to surface effects or crystal grain structure in the particles.Comment: 4 pages, 3 figure

Multiscale analysis and simulation of a signalling process with surface diffusion

We present and analyze a model for cell signaling processes in biological tissues. The model includes diffusion and nonlinear reactions on the cell surfaces and both inter- and intracellular signaling. Using techniques from the theory of two-scale convergence as well the unfolding method, we show convergence of the solutions to the model to solutions of a two-scale macroscopic problem. We also present a two-scale bulk-surface finite element method for the approximation of the macroscopic model. We report on some benchmarking results as well as numerical simulations in a biologically relevant regime that illustrate the influence of cell-scale heterogeneities on macroscopic concentrations

Spontaneous symmetry breaking in rotating condensates of ultracold atoms

We describe an equilibrium state of a rotating trapped atomic condensate, which is characterized by a non-zero internal circulation and spontaneous breaking of the rotational O(2) symmetry with all three major semiaxes of the condensate having different values. The macroscopic rotation of the condensate is supported by a mesh of quantized vortices, whose number density is a function of internal circulation. The oscillation modes of this state are computed and the Goldstone mode associated with the loss of the symmetry is identified. The possible avenues for experimental identification this state are discussed.Comment: v1: 4 pages, 3 figures; v2: 5 pages, 4 figures, minor changes, matches published versio

Electrodynamics in Friedmann-Robertson-Walker Universe: Maxwell and Dirac fields in Newman-Penrose formalism

Maxwell and Dirac fields in Friedmann-Robertson-Walker spacetime is investigated using the Newman-Penrose method. The variables are all separable, with the angular dependence given by the spin-weighted spherical harmonics. All the radial parts reduce to the barrier penetration problem, with mostly repulsive potentials representing the centrifugal energies. Both the helicity states of the photon field see the same potential, but that of the Dirac field see different ones; one component even sees attractive potential in the open universe. The massless fields have the usual exponential time dependencies; that of the massive Dirac field is coupled to the evolution of the cosmic scale factor $a$. The case of the radiation filled flat universe is solved in terms of the Whittaker function. A formal series solution, valid in any FRW universe, is also presented. The energy density of the Maxwell field is explicitly shown to scale as $a^{-4}$. The co-moving particle number density of the massless Dirac field is found to be conserved, but that of the massive one is not. Particles flow out of certain regions, and into others, creating regions that are depleted of certain linear and angular momenta states, and others with excess. Such current of charged particles would constitute an electric current that could generate a cosmic magnetic field. In contrast, the energy density of these massive particles still scales as $a^{-4}$.Comment: 18 pages including 9 figure