Probability for Primordial Black Holes in Multidimensional Universe with Nonlinear Scalar Curvature Terms

We investigate multi-dimensional universe with nonlinear scalar curvature terms to evaluate the probability of creation of primordial black holes. For this we obtain Euclidean instanton solution in two different topologies: (a) $S^{D-1}$ - topology which does not accommodate primordial black holes and (b) $S^1\times S^{D-2}$-topology which accommodates a pair of black holes. The probability for quantum creation of an inflationary universe with a pair of black holes has been evaluated assuming a gravitational action which is described by a polynomial function of scalar curvature with or without a cosmological constant ($\Lambda$) using the framework of semiclassical approximation of Hartle-Hawking boundary conditions. We discuss here a class of new gravitational instantons solution in the $R^4$-theory which are relevant for cosmological model building.Comment: 18 pages, no figure. accepted in Phys. Rev.

The Sensitivity of Multidimensional Nova Calculations to the Outer Boundary Conditions

Multidimensional reactive flow models of accreted hydrogen rich envelopes on top of degenerate cold white dwarfs are very effective tools for the study of critical, non spherically symmetric, behaviors during the early stages of nova outbursts. Such models can shed light both on the mechanism responsible for the heavy element enrichment observed to characterize nova envelope matter and on the role of perturbations during the early stages of ignition of the runaway. The complexity of convective reactive flow in multi-dimensions makes the computational model itself complex and sensitive to the details of the numerics. In this study, we demonstrate that the imposed outer boundary condition can have a dramatic effect on the solution. Several commonly used choices for the outer boundary conditions are examined. It is shown that the solutions obtained from Lagrangian simulations, where the envelope is allowed to expand and mass is being conserved, are consistent with spherically symmetric solutions. In Eulerian schemes which utilize an outer boundary condition of free outflow, the outburst can be artificially quenched.Comment: 12 Pages 3 figures; Accepted for publication in the Astrophysical Journa

Optimization of grazing incidence mirrors and its application to surveying X-ray telescopes

Grazing incidence mirrors for X-ray astronomy are usually designed in the parabola-hyperbola (Wolter I) configuration. This design allows for optimal images on-axis, which however degrade rapidly with the off-axis angle. Mirror surfaces described by polynomia (with terms higher than order two), have been put forward to improve the performances over the field of view. Here we present a refined procedure aimed at optimizing wide-field grazing incidence telescopes for X-ray astronomy. We improve the angular resolution over existing (wide-field) designs by ~ 20%. We further consider the corrections for the different plate scale and focal plane curvature of the mirror shells, which sharpen by another ~ 20% the image quality. This results in a factor of ~ 2 reduction in the observing time needed to achieve the same sensitivity over existing wide-field designs and of ~ 5 over Wolter I telescopes. We demonstrate that such wide-field X-ray telescopes are highly advantageous for deep surveys of the X-ray sky.Comment: 8 pages 4 figures. Accepted for publication on A&A (macro included

Unified approach to study quantum properties of primordial black holes, wormholes and of quantum cosmology

We review the anomaly induced effective action for dilaton coupled spinors and scalars in large N and s-wave approximation. It may be applied to study the following fundamental problems: construction of quantum corrected black holes (BHs), inducing of primordial wormholes in the early Universe (this effect is confirmed) and the solution of initial singularity problem. The recently discovered anti-evaporation of multiple horizon BHs is discussed. The existance of such primordial BHs may be interpreted as SUSY manifestation. Quantum corrections to BHs thermodynamics maybe also discussed within such scheme.Comment: LaTeX file and two eps files, to appear in MPLA, Brief Review

Spectrums of Black Hole in de Sitter Spacetime with Highly Damped Quasinormal Modes: High Overtone Case

Motivated by recent physical interpretation on quasinormal modes presented by Maggiore, the adiabatic quantity method given by Kunstatter is used to calculate the spectrums of a non-extremal Schwarzschild de Sitter black hole in this paper, as well as electrically charged case. According to highly damped Konoplya and Zhidenko's numerical observational results for high overtone modes\cite{Konoplya}, we found that the asymptotic non-flat spacetime structure leads two interesting facts as followings: (i) near inner event horizon, the area and entropy spectrums, which are given by $A_{en} = 8 n_1 \pi \hbar$, $S_{en} = 2\pi n_1\hbar$, are equally spaced accurately. (ii) However, near outer cosmological horizon the spectrums, which are in the form of $A_{cn} = 16 n_2 \pi \hbar - \sqrt{\frac{48\pi}{\Lambda}A_{cn} - 3 A_{cn}^2}$, $S_{cn} = 4 \pi n_2 \hbar - \sqrt{\frac{3\pi}{\Lambda}A_{cn} - 3/16 A_{cn}^2}$, are not markedly equidistant. Finally, we also discuss the electrically charged case and find the black holes in de Sitter spacetime have similar quantization behavior no matter with or without charge.Comment: 12 pages, 2 firures, published versio

Real Scalar Field Scattering with Polynomial Approximation around Schwarzschild-de Sitter Black-hole

As one of the fitting methods, the polynomial approximation is effective to process sophisticated problem. In this paper, we employ this approach to handle the scattering of scalar field around the Schwarzschild-de Sitter black-hole. The complex relationship between tortoise coordinate and radial coordinate is replaced by the approximate polynomial. The Schr$\ddot{o}$dinger-like equation, the real boundary conditions and the polynomial approximation construct a full Sturm-Liouville type problem. Then this boundary value problem can be solved numerically according to two limiting cases: the first one is the Nariai black-hole whose horizons are close to each other, the second one is when the horizons are widely separated. Compared with previous results (Brevik and Tian), the field near the event horizon and cosmological horizon can have a better description.Comment: revtex4 source file, 11 pages, 8 figure

Solutions of Minimal Four Dimensional de Sitter Supergravity

Pseudo-supersymmetric solutions of minimal $N=2$, $D=4$ de Sitter supergravity are classified using spinorial geometry techniques. We find three classes of solutions. The first class of solution consists of geometries which are fibrations over a 3-dimensional manifold equipped with a Gauduchon-Tod structure. The second class of solution is the cosmological Majumdar-Papapetrou solution of Kastor and Traschen, and the third corresponds to gravitational waves propagating in the Nariai cosmology.Comment: 17 Pages. Minor correction to section 4; equation (4.21) corrected and (old) equation (4.26) deleted; the final result is unchange

Possible quantum instability of primordial black holes

Evidence for the possible existence of a quantum process opposite to the famous Hawking radiation (evaporation) of black holes is presented. This new phenomenon could be very relevant in the case of exotic multiple horizon Nariai black holes and in the context of common grand unified theories. This is clearly manifested in the case of the SO(10) GUT, that is here investigated in detail. The remarkable result is obtained, that anti-evaporation can occur there only in the SUSY version of the theory. It is thus concluded that the existence of primordial black holes in the present Universe might be considered as an evidence for supersymmetry.Comment: LaTeX, 7 pages, version to appear in PRD Rapid Communication

Reheating and turbulence

We show that the ''turbulent'' particle spectra found in numerical simulations of the behavior of matter fields during reheating admit a simple interpretation in terms of hydrodynamic models of the reheating period. We predict a particle number spectrum $n_{k}\propto k^{-\alpha}$ with $\alpha \sim 2$ for $k\to 0.$Comment: 10 pages, one figure included in tex

Spherically symmetric black holes in minimally modified self-dual gravity

We discuss spherically symmetric black holes in the modified self-dual theory of gravity recently studied by Krasnov, obtained adding a Weyl-curvature dependent `cosmological term' to the Plebanski lagrangian for general relativity. This type of modified gravity admits two different types of singularities: one is a true singularity for the theory where the fundamental fields of the theory, as well as the (auxiliary) spacetime metric, become singular, and the other one is a milder "non-metric singularity" where the metric description of the spacetime breaks down but the fundamental fields themselves are regular. We first generalise this modified self-dual gravity to include Maxwell's field and then study basic features of spherically symmetric, charged black holes, with particular focus on whether these two types of singularities are hidden or naked. We restrict our attention to minimal forms of the modification, and find that the theory exhibits `screening' effects of the electric charge (or `anti-screening', depending upon the sign of the modification term), in the sense that it leads to the possibility of charging the black hole more (or less) than it would be possible in general relativity without exposing a naked singularity. We also find that for any (even arbitrarily large) value of charge, true singularities of the theory appear to be either achronal (non-timelike) covered by the hypersurface of a harmless non-metric singularity, or simply hidden inside at least one Killing horizon.Comment: 42 pages, many colour figures. v2: discussion of the conformal ambiguity improved, references added. v3: amended to match published versio