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O. B. Zaslavskii

Publications and source records attributed to O. B. Zaslavskii.

138 records · Page 8Linked to original sources

Two-dimensional dilaton gravity and spacetimes with finite curvature at the horizon away from the Hawking temperature

It is shown that static solutions with a finite curvature at the horizon may exist in dilaton gravity at temperatures $T\neq T_{H}$ (including T=0) where $T_{H} $is the Hawking one. Hawking radiation is absent and the state of a system represents thermal excitation over the Boulware vacuum. The horizon remains unattainable for a observer because of thermal divergences in the stress-energy of quantum fields there. However, the curvature at the horizon is finite, when measured from outside, since these divergences are compensated by those in gradients of a dilaton field. Spacetimes under consideration are geodesically incomplete and the coupling between dilaton and gravity diverges at the horizon, so we have ''singularity without singularity''.

hep-th↗

Semi-infinite throats at finite temperature and static solutions in exactly solvable models of 2d dilaton gravity

Found is a general form of static solutions in exactly solvable models of 2d dilaton gravity at finite temperature. We reveal a possibility for the existence of everywhere regular solutions including black holes, semi-infinite throats and star-like configurations. In particular, we consider the Bose-Parker-Peleg (BPP) model which possesses a semi-infinite throat and analyze it at finite temperature. We also suggest generalization of the BPP model in which the appearance of semi-infinite throat has a generic character and does not need special fine tuning between parameters of the solution.

hep-th↗

Tunnelling series in terms of perturbation theory for quantum spin systems

Considered is quantum tunnelling in anisotropic spin systems in a magnetic field perpendicular to the anisotropy axis. In the domain of small field the problem of calculating tunnelling splitting of energy levels is reduced to constructing the perturbatio n series with degeneracy, the order of degeneracy being proportional to a spin value. Partial summation of this series taking into account ''dangerous terms'' with small denominators is performed and the value of tunnelling splitting is calculated with allowance for the first correction with respect to a magnetic field.

quant-ph↗

Spin systems, spin coherent states and quasi-exactly solvable models

Spin coherent states play a crucial role in defining QESM (quasi-exactly solvable models) establishing a strict correspondence between energy spectra of spin systems and low-lying quantum states for a particle moving in a potential field of a certain form. Spin coherent states are also used for finding the Wigner-Kirkwood expansion and quantum corrections to energy quantization rules. The closed equation which governs dynamics of a quantum system is obtained in the spin coherent representation directly for observable quantities.

quant-ph↗

Exactly solvable models of two-dimensional dilaton gravity and quantum eternal black holes

New approach to exact solvability of dilaton gravity theories is suggested which appeals directly to structure of field equations. It is shown that black holes regular at the horizon are static and their metric is found explicitly. If a metric possesses singularities the whole spacetime can be divided into different sheets with one horizon on each sheet between neighboring singularities with a finite value of dilaton field (addition horizons may arise at infinite value of it), neighboring sheets being glued along the singularity. The position of singularities coincide with the values of dilaton in solutions with a constant dilaton field. Quantum corrections to the Hawking temperature vanish. For a wide subset of these models the relationship between the total energy and the total entropy of the quantum finite size system is the same as in the classical limit. For another subset the metric itself does not acquire quantum corrections. The present paper generalizes Solodukhin's results on the RST model in that instead of a particular model we deal with whole classes of them. Apart from this, the found models exhibit some qualitatively new properties which are absent in the RST model. The most important one is that there exist quantum black holes with geometry regular everywhere including infinity.

hep-th↗

Two- and Many-Dimensional Quasi-Exactly Solvable Models With An Inhomogeneous Magnetic Field

Let group generators having finite-dimensional representation be realized as Hermitian linear differential operators without nhomogeneous terms as takes place, for example, for the SO(n) group. Then orresponding group Hamiltonians containing terms linear in generators (along with quadratic ones) give rise to quasi-exactly solvable models with a magnetic field in a curved space. In particular, in the two-dimensional case such models are generated by quantum tops. In the three-dimensional one for the SO(4) Hamiltonian with an isotropic quadratic part the manifold within which a quantum particle moves has the geometry of the Einstein universe.

solv-int↗

Horizon/Matter Systems near the Extreme State

It is shown that in the extreme limit with a zero surface gravity but nonzero local temperature the limiting metric of a generic static black hole is determined by a metric induced on a horizon and one function of two coordinates, stress-energy tensor of a source picking up its values from a horizon. The limiting procedure is extended to rotating black holes. If the extreme limit is due to merging a black hole horizon and cosmological one both horizons are always in thermal equilibrium in this limit. This is proved for a generic case of static or axially-symmetrical rotating spacetimes.

gr-qc↗

Comment on ''Understanding the Area Proposal for Extremal Black Hole Entropy''

A. Ghosh and P. Mitra made the proposal how to explain the area law for the entropy of extreme black holes in some model calculations. I argue that their approach implicitly operates with strongly singular geometries and says nothing about the contribution of regular metrics of extreme black holes into the partition function.

hep-th↗

Entropy of Quantum Fields for Nonextreme Black Holes in the Extreme Limit

Nonextreme black hole in a cavity within the framework of the canonical or grand canonical ensemble can approach the extreme limit with a finite temperature measured on a boundary located at a finite proper distance from the horizon. In spite of this finite temperature, it is shown that the one-loop contribution $S_{q\text{ }}$of quantum fields to the thermodynamic entropy due to equilibrium Hawking radiation vanishes in the limit under consideration. The same is true for the finite temperature version of the Bertotti-Robinson spacetime into which a classical Reissner-Nordström black hole turns in the extreme limit. The result $S_{q}=0$ is attributed to the nature of a horizon for the Bertotti-Robinson spacetime.

gr-qc↗

Dilaton black holes in grand canonical ensemble near the extreme state

Dilaton black holes with a pure electric charge are considered in a framework of a grand canonical ensemble near the extreme state. It is shown that there exists such a subset of boundary data that the Hawking temperature smoothly goes to zero to an infinite value of a horizon radius but the horizon area and entropy are finite and differ from zero. In string theory the existence of a horizon in the extreme limit is due to the finiteness of a system only.

gr-qc↗

Geometry of nonextreme black holes near the extreme state

Nonextreme black hole in a cavity can achieve the extreme state with a zero surface gravity at a finite temperature on a boundary, the proper distance between the boundary and the horizon being finite. The classical geometry in this state is found explicitly for four-dimensional spherically-symmetrical and 2+1 rotating holes. In the first case the limiting geometry depends only on one scale factor and the whole Euclidean manifold is described by the Bertotti-Robinson spacetime. The general structure of a metric in the limit under consideration is also found with quantum corrections taken into account. Its angular part represents two-sphere of a constant radius. In all cases the Lorentzian counterparts of the metrics are free from singularities.

gr-qc↗