arXiv subjects

Mikhail Z. Iofa

Publications and source records attributed to Mikhail Z. Iofa.

At least 19 recordsLinked to original sources

arXiv2022

On the mass function at the inner horizon of a regular black hole

Calculations of the inner mass function of the Hayward regular black hole with fluxes are reviewed and rederived. We present detailed calculations of the inner mass function in two forms of the Ori approach (the ingoing flux is continuous, the outgoing flux is modeled by a thin null shell) and compare them with calculations in Reissner-Nordstrom black hole. A formal reason of different results is discussed. The energy density of scalar perturbations propagating from the event horizon into the Hayward black hole measured by a free falling observer near the inner horizon is calculated.

gr-qc↗

arXiv2021

Surface charge of horizon symmetries of a black hole with supertranslation field

Near-horizon symmetries are studied for static black hole solutions to Einstein equations containing supertranslation field. We consider general diffeomorphisms which preserve the gauge and the near-horizon structure of the metric. Diffeomorphisms are generated by the vector fields and form a group of near-horizon symmetries. The densities of variation of the surface charge associated to asymptotic horizon symmetries of the metric are calculated in different coordinate systems connected by "large" transformations which change supertranslation field in the metric. Integrability of the variations of surfacecharge is considered in different coordinate systems. The case of integrable variation of the surface charge is studied in detail.

gr-qc↗

arXiv2020

Black holes with supertranslation field, "large transformations" and Israel theorem

An axial-symmetric vacuum solution of the Einstein equations containing a supertranslation field diffeomorphic to the Schwarzschild solution is discussed in the context of Israel theorem. The metric satisfies all conditions of the Israel theorem, except for the condition on the form of the metric at spatial infinity. Nevertheless, following the steps of the proof of the theorem we show that the proof applies to the metric with supertranslation field and the (transformed) metric used in the proof is spherically symmetric. We explain the source of the seeming discrepancy connected with the use of "large" transformations changing supertranslation field in the metric.

gr-qc↗

arXiv2019

Horizon symmetries of black holes with supertranslation field

Near-horizon symmetries are studied for black hole solutions to Einstein equations containing supertranslation field constructed by Compere and Long. The metric is transformed to variables in which the horizon is located at the surface $r=2M$, where $M$ is the mass of black hole. We consider general diffeomorphisms which preserve the gauge and the near-horizon structure of the metric and find the corresponding transformations of metric components. We review the action of the generators of supertranslations preserving the static gauge of the metric and determine a subgroup of supertranslations preserving the gauge and near-horizon structure of the metric. Variation of the surface charge corresponding to the Killing vectors of asymptotic horizon symmetries is calculated. Sufficient conditions of integrability of the variation of the surface charge to a closed integral form are found and an example of metrics with integrable charge variation is discussed.

gr-qc↗

arXiv2019

Near-horizon symmetries of the Schwarzschild black hole with supertranslation field

Using the exact solution to Einstein equations of Compere and Long for the Schwarzschild metric containing supertranslation field, we study the near-horizon symmetries of the metric. We consider class of metrics with supertranslation field depending only on a spherical angle $θ$. After reviewing the action of supertranslations preserving the static gauge of the metric, we study general transformations preserving the near-horizon form of the metric. We determine the asymptotic Killing vectors and calculate the charge corresponding to the asymptotic symmetries preserving the form of the metric at the horizon.

hep-th↗

arXiv2017

Thermal Hawking radiation of black hole with supertranslation field

Using the analytical solution for the Schwarzschild metric containing supertranslation field, we consider two main ingredients of calculation of the thermal Hawking black hole radiation: solution for eigenmodes of the d'Alambertian and solution of the geodesic equations for null geodesics. For calculation of Hawking radiation it is essential to determine the behavior of both the eigenmodes and geodesics in the vicinity of horizon. The equation for the eigenmodes is solved, first, perturbatively in the ratio $O(C)/M$ of the supertranslation field to the mass of black hole, and, next, non-perturbatively in the near- horizon region. It is shown that in any order of perturbation theory solution for the eigenmodes in the metric containing supertranslation field differs from solution in the pure Schwarzschild metric by terms of order $L^{1/2}= (1-2M/r)^{1/2}$. In the non-perturbative approach, solution for the eigenmodes differs from solution in the Schwarzschild metric by terms of order $L^{1/2}$ which vanish on horizon. Using the simplified form of geodesic equations in vicinity of horizon, it is shown that in vicinity of horizon the null geodesics have the same behavior as in the Schwarzschild metric. As a result, the density matrices of thermal radiation in both cases are the same.

hep-th↗

arXiv2016

Density matrix of radiation of black hole with fluctuating horizon

The density matrix of Hawking radiation is calculated in the model of black hole with fluctuating horizon. Quantum fluctuations smear the classical horizon of black hole and modify the density matrix of radiation producing the off-diagonal elements. The off-diagonal elements may store information of correlations between radiation and black hole. The smeared density matrix was constructed by convolution of the density matrix calculated with the instantaneous horizon with the Gaussian distribution over the instantaneous horizons. The distribution has the extremum at the classical radius of the black hole and the width of order of the Planck length. Calculations were performed in the model of black hole formed by the thin collapsing shell which follows a trajectory which is a solution of the matching equations connecting the interior and exterior geometries.

gr-qc↗

arXiv2016

The notes on thin shells

Geometry of the spacetime with a spherical shell embedded in it is studied in two coordinate systems - in Kodama-Schwarzschild coordinates and in Gaussian normal coordinates. We consider transformations between the coordinate systems as in the 4D spacetime so as at the surface $§$ swept in the spacetime by the spherical shell. Extrinsic curvatures of the surface swept by the shell are calculated in both coordinate systems. Applications to the Israel junction conditions are discussed.

gr-qc↗

arXiv2015

Energy-momentum tensor of bouncing gravitons

In models of the Universe with extra dimensions gravity propagates in the whole space-time. Graviton production by matter on the brane is significant in the early hot Universe. In a model of 3-brane with matter embedded in 5D space-time conditions for gravitons emitted from the brane to the bulk to return back to the brane are found. For a given 5-momentum of graviton falling back to the brane the interval between the times of emission and return to the brane is calculated. A method to calculate contribution to the energy-momentum tensor from multiple graviton bouncings is developed. Explicit expressions for contributions to the energy-momentum tensor of gravitons which have made one, two and three bounces are obtained and their magnitudes are numerically calculated. These expressions are used to solve the evolution equation for dark radiation. A relation connecting reheating temperature and the scale of extra dimension is obtained. For the reheating temperature $T_R\sim 10^6 GeV$ we estimate the scale of extra dimension $\m$ to be of order $10^{-9} GeV\,\,\, (\m^{-1}\sim 10^{-5} cm )$.

hep-th↗

arXiv2014

Microscopic entropy of trapping horizon

In the Carlip-Majhi-Padmanabhan approach, we calculate microscopic entropy of trapping (apparent) horizon of the FRW metric. We solve Killing equations for $t,r$ part of the metric without fixing {\it a piori} the form of the scaling factor $a(t)$ which is determined from the requirement of consistency of Killing equations. Further restrictions on the form of the Killing vector follow from the requirement that Killing vector is null at the trapping horizon at all $t$. Applying the technique used to calculate microscopic entropy of Killing horizons, we calculate microscopic entropy of trapping horizon. Using the explicit form of Killing vector, we verify that identities used in calculation of the central term of Virasoro algebra for Killing horizons of black holes are valid in the present case.

hep-th↗

arXiv2014

Contribution of bouncing gravitons to the energy-momentum tensor

In a model of 3-brane with matter embedded in 5D space-time conditions for gravitons emitted from the brane to the bulk to return back to the brane are found. A method to calculate contribution to the energy-momentum tensor from multiple bouncing gravitons is developed. Contribution to the energy momentum tensor from gravitons of the first bounce is calculated. The result is much smaller than those obtained previously.

hep-th↗

arXiv2013

Bouncing of gravitons emitted from the brane to the bulk back to the brane

Solutions of geodesic equations describing propagation of gravitons in the bulk are studied in a cosmological model with one extra dimension. Brane with matter is embedded in the bulk. It is shown that in the period of early cosmology gravitons emitted from the brane to the bulk under certain conditions can return back to the brane. The model is discussed in two alternative approaches: (i) brane with static metric moving in the AdS space, and (ii) brane located at a fixed position in extra dimension with non-static metric. Transformation of coordinates from the one picture to another is performed. In both approaches conditions for gravitons emitted to the bulk to come back to the brane are found.

hep-th↗

arXiv2012

Connection between two forms of extra-dimensional metrics revisited

5D cosmological model with 3-brane with matter is considered. The brane divides bulk in two AdS half spaces. Geometry of the model can be described by two types of coordinates: in the first setting the metric is static and the brane is moving in the bulk, in the second approach the metric is time-dependent and the brane is located at a fixed position in the bulk. Coordinate transformation connecting two coordinate systems is constructed.

hep-th↗

arXiv2011

Graviton emission from the brane in the bulk in a model with extra dimension

In a model of 3-brane embedded in 5D space-time we calculate the graviton emission from the brane to the bulk. Matter is confined to the brane, gravitons produced in reactions of matter on the brane escape to the bulk. The Einstein equations which are modified by the terms due to graviton production are solved perturbatively, the leading order being that without the graviton production. In the period of late cosmology, in which in the generalized Friedmann equation the term linear in the energy density of matter in dominant, we calculate the spectrum of gravitons (of the tower of Kaluza-Klein states) and the collision integral in the Boltzmann equation. We find the energy-momentum tensor of the emitted gravitons in the bulk, and using it show that corrections due to graviton production to the leading-order terms in the Einstein equations are small, and the perturbative approach is justified. We calculate the difference of abundances of ${}^4 He$ produced in primordial nucleosynthesis in the models with and without the graviton production, and find that the difference is a very small number, much smaller than that estimated previously.

gr-qc↗

arXiv2009

Cosmological constraints on parameters of one-brane models with extra dimension

We study some aspects of cosmologies in 5D models with one infinite extra dimension. Matter is confined to the brane, gravity extends to the bulk. Models with positive and negative tension of the brane are considered. Cosmological evolution of the 4D world is described by warped solutions of the generalized Friedmann equation. Cosmological solutions on the brane are obtained with the input of the present-time observational cosmological parameters. We estimate the age of the Universe and abundance of ${}^4 He$ produced in primordial nucleosynthesis in different models. Using these estimates we find constraints on dimensionless combinations of the 5D gravitational scale, scale of the warp factor and coupling at the 4D curvature term in the action.

astro-ph.CO↗

arXiv2007

A note on cosmology in a brane model

We study some aspects of cosmology in a five-dimensional model with matter, radiation and cosmological constant on the four-dimensional brane(s) and without matter in the bulk. The action of the model does not contain explicit curvature terms on the the brane(s). We obtain solution of the generalized Friedman equation as a function of dimensionless ratio of the scales $b^2 = \frac{μM^2_{pl}}{M^3}$ ($μ$ is the scale in the warp factor in the 5D metric which is taken of order $10^{3÷4}GeV$, $M\geqμ$ is the $5D$ fundamental scale). We assume that there is a hierarchy between 4D and 5D scales. For $b^2 =O(1)$ the age of the Universe is found comparable, but below the current experimental value, for $b^2\gg 1$ it is obtained much smaller than the experimental bound. Because time dependence of temperature of the Universe in the 5D model is different from that in the standard cosmology, the abundance of ${}^4$He produced in the primordial nucleosynthesis is obtained about three times more than in the standard cosmology.

gr-qc↗

arXiv2002

Dyonic Black Holes with String-Loop Corrections

In heterotic string theory compactified to four dimensions with N=2 supersymmetry, string-loop corrections to the universal sector of the low-energy effective action are studied. Within the framework of N=2 supersymmetric formulation of the theory, in the first order in string coupling constant, we solve the system of the loop-corrected Maxwell and Killing spinor equations. Taking as the in-put the tree-level dyonic black hole solution, we calculate string-loop corrections to the string tree-level metric and moduli of dyonic black hole.

hep-th↗

arXiv2002

Near-horizon behavior of string-loop-corrected dyonic black holes

Dyonic black holes with string-loop corrections are studied in the near-horizon region. In perturbative heterotic string theory compactified to four dimensions with N=2 supersymmetry, in the first order in string-loop expansion parameter, we solve the system of Maxwell and Killing spinor equations for dyonic black hole. At the horizon, the string-loop-corrected solution displays restoration of spontaneously broken supersymmetry.

hep-th↗