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New methods in the theory of quantum spin systems
Abstract Recently developed methods to investigate quantum spin systems are reviewed. These methods are based on somewhat unconventional applications of the spin coherent state technique developed inExpand
Regular black holes and energy conditions
Abstract We establish the relationship between the space–time structure of regular spherically-symmetrical black holes and the character of violation of the strong energy condition (SEC). It is shownExpand
Geometry of nonextreme black holes near the extreme state
A 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 beingExpand
Acceleration of particles by nonrotating charged black holes?
Recently, in the series of works a new effect of acceleration of particles by black holes has been found. Under certain conditions, the energy in the center-of-mass system can become infinitelyExpand
Acceleration of particles as a universal property of rotating black holes
We argue that the possibility of having infinite energy in the center-of-mass frame of colliding particles is a generic property of rotating black holes. We suggest a general model-independentExpand
Traversable wormholes: Minimum violation of the null energy condition revisited
It was argued in literature that traversable wormholes can exist with an arbitrarily small violation of null energy conditions. I show that if the amount of exotic material near the wormhole throatExpand
Spin tunneling and the effective potential method
Abstract Spin tunneling is described based on the exact correspondence between the spin system and a particle moving in a potential field. In the general case of two-axis anisotropy the potential isExpand
Exactly solvable model of a wormhole supported by phantom energy
We have found a simple exact solution of spherically symmetrical Einstein equations describing a wormhole for an inhomogeneous distribution of the phantom energy. The equation of state is linear butExpand
Curvature tensors on distorted Killing horizons and their algebraic classification
We consider generic static spacetimes with Killing horizons and study properties of curvature tensors in the horizon limit. It is determined that the Weyl, Ricci, Riemann and Einstein tensors areExpand