arXiv subjects

Andrei Zelnikov

Publications and source records attributed to Andrei Zelnikov.

45 records · Page 3Linked to original sources

arXiv2012

Higher-dimensional Kundt waves and gyratons

We present and analyze exact solutions of the Einstein-Maxwell equations in higher dimensions which form a large subclass of the Kundt family of spacetimes. We assume that the cosmological constant may be nonvanishing, and the matter consists of a background aligned electromagnetic field and an additional pure radiation (gyratonic) field with a spin. We show that the field equations reduce to a set of linear equations on the transverse space which can be solved exactly and expressed in terms of the Green functions. We thus find explicit exact gyratonic gravitational and electromagnetic fields created by a radiation beam of null matter with arbitrary profiles of energy density and angular momenta. In the absence of the gyratonic matter we obtain pure nonexpanding higher-dimensional gravitational waves. In particular, we investigate gyratons and waves propagating on backgrounds which are a direct-product of 2-spaces of constant curvature. Such type D or 0 background spacetimes generalize 4-dimensional Nariai, anti-Nariai and Plebanski-Hacyan universes, and conformally flat Bertotti-Robinson and Minkowski spaces. These spacetimes belong to a wider class of spaces which admit the Kahler structure related to the background magnetic field. The obtained wave and gyraton solutions are also members of the recently discussed class of spacetimes with constant scalar invariants (CSI) of the curvature tensor.

gr-qc↗

arXiv2009

Gyratons on direct-product spacetimes

We present and analyze exact gyraton and nonexpanding gravitational wave solutions of algebraic type II on backgrounds which are a direct-product of two 2-spaces of constant curvature, or more general type D spacetimes. This family of electro-vacuum background spacetimes contains the Nariai, anti-Nariai and Plebanski-Hacyan universes, conformally flat Bertotti-Robinson and Minkowski spaces. The gyraton solutions are given in a simple Kundt metric form. They belong to the recently discussed class of spacetimes with constant scalar invariants (CSI) of the curvature tensor. We show that the Einstein equations reduce to a set of linear equations on the transverse 2-space which can be explicitly solved using the Green functions.

gr-qc↗

arXiv2008

Non-minimal scalar fields in 2D de Sitter and dilaton black holes

We study non-minimal quantum fields in the gravitational field of 2-dimensional dilaton black holes and the de Sitter spacetime. We found that the Green functions for non-minimal massless fields in a particular class of dilaton black holes and in the de Sitter spacetime are almost identical. Using this symmetry exact solutions are derived for quasinormal modes and bound states in these background geometries. The problem of stability of dilaton black holes is discussed.

hep-th↗

arXiv2007

Apparent horizon formation in the head-on collision of gyratons

The gyraton model describes a gravitational field of an object moving with the velocity of light which has finite energy and spin distributed during some finite time interval $L$. A gyraton may be considered as a classical toy model for a quantum wave packet of high-energy particles with spin. In this paper we study a head-on collision of two gyratons and black hole formation in this process. The goal of this study is to understand the role of the gravitational spin-spin interaction in the process of mini-black-hole formation in particle collisions. To simplify the problem we consider several gyraton models with special profiles of the energy and spin density distribution. For these models we study the apparent horizon (AH) formation on the future edge of a spacetime region before interaction. We demonstrate that the AH forms only if the energy duration and the spin are smaller than some critical values, while the length of the spin distribution should be at least of the order of the system gravitational radius. We also study gravitational spin-spin interaction in the head-on collision of two gyratons under the assumption that the values of gyraton spins are small. We demonstrate that the metric in the interaction region for such gyratons depends on the relative helicities of incoming gyratons, and the collision of gyratons with oppositely directed spins allows the AH formation in a larger parameter region than in the collision of the gyratons with the same direction of spins. Some applications of the obtained results to the mini-black-hole production at the Large Hadron Collider in TeV gravity scenarios are briefly discussed.

gr-qc↗

arXiv2006

Gravitational field of charged gyratons

We study relativistic gyratons which carry an electric charge. The Einstein-Maxwell equations in arbitrary dimensions are solved exactly in the case of a charged gyraton propagating in an asymptotically flat metric.

gr-qc↗

arXiv2005

Gravitational field of relativistic gyratons

The metric ansatz is used to describe the gravitational field of a beam-pulse of spinning radiation (gyraton) in an arbitrary number of spacetime dimensions D. First we demonstrate that this metric belongs to the class of metrics for which all scalar invariants constructed from the curvature and its covariant derivatives vanish. Next, it is shown that the vacuum Einstein equations reduce to two linear problems in (D-2)-dimensional Euclidean space. The first is to find the static magnetic potential created by a point-like source. The second requires finding the electric potential created by a point-like source surrounded by given distribution of the electric charge. To obtain a generic gyraton-type solution of the vacuum Einstein equations it is sufficient to allow the coefficients in the corresponding harmonic decompositions of solutions of the linear problems to depend arbitrarily on retarded time and substitute the obtained expressions in the metric ansatz. We discuss properties of the solutions for relativistic gyratons and consider special examples.

hep-th↗

arXiv2005

Relativistic gyratons in asymptotically AdS spacetime

We study the gravitational field of a spinning radiation beam-pulse (a gyraton) in a D-dimensional asymptotically AdS spacetime. It is shown that the Einstein equations for such a system reduce to a set of two linear equations in a (D-2)-dimensional space. By solving these equations we obtain a metric which is an exact solution of gravitational equations with the (negative) cosmological constant. The explicit metrics for 4D and 5D gyratons in asymptotically AdS spacetime are given and their properties are discussed.

hep-th↗

arXiv2001

Unruh Radiation, Holography and Boundary Cosmology

A uniformly acclerated observer in anti-deSitter space-time is known to detect thermal radiation when the acceleration exceeds a critical value. We investigate the holographic interpretation of this phenomenon. For uniformly accelerated trajectories transverse to the boundary of the AdS space, the hologram is a blob which expands along the boundary. Observers on the boundary co-moving with the hologram become observers in cosmological space-times. For supercritical accelerations one gets a Milne universe when the holographic screen is the boundary in Poincare coordinates, while for the boundary in hyperspherical coordinates one gets deSitter spacetimes. The presence or absence of thermality is then interpreted in terms of specific classes of observers in these cosmologies.

hep-th↗

arXiv1997

Finite Temperature Nonlocal Effective Action for Scalar Fields

Scalar fields at finite temperature are considered in four dimensional ultrastatic curved spacetime. One loop nonlocal effective action at finite temperature is found up to the second order in curvature expansion. This action is explicitly infrared finite. In the high temperature expansion of free energy, essentially nonlocal terms linear in temperature are derived.

hep-th↗