Martin Kološ — Page 3

arXiv2013

Acceleration of particles in spacetimes of black string

The particle acceleration mechanism in $S^2 \times\mathbb{R}^1$ topology, namely in the spacetime of the five-dimensional compact black string has been studied. The expression of center-of-mass energy of the colliding neutral particles near static black string has been found. The collision of charged particle moving at the innermost stable circular orbit with neutral particle coming from infinity have been considered when black string is immersed in external uniform magnetic field. It has been shown that the unlimited center-of-mass energy can be approached in case of the extremal rotation of the black string which is similar to the analogous effect in the Kerr spacetime. We have also obtained that the scattering energy of particles in the center-of-mass system can take arbitrary large values not only for extremal black string but also for nonextremal one. It has been derived that the presence of the extra dimension can, in principle, increase the upper limit of efficiency of energy extraction from the extremely rotating black string up to $203\%$ versus to $143\%$ which can be extracted from the extreme Kerr black hole.

gr-qc↗

arXiv2011

Current-carrying string loops in black-hole spacetimes with a repulsive cosmological constant

Current-carrying string loop dynamics in Schwarzschild-de Sitter spacetimes characterized by the cosmological parameter λ=1/3ΛM^2 is investigated. With attention concentrated to the axisymmetric motion of string loops it is shown that the resulting motion is governed by the presence of an outer tension barrier and an inner angular momentum barrier that are influenced by the black hole gravitational field given by the mass M and the cosmic repulsion given by the cosmological constant Λ. The gravitational attraction could cause capturing of the string having low energy by the black hole or trapping in its vicinity; with high enough energy, the string can escape (scatter) to infinity. The role of the cosmic repulsion becomes important in vicinity of the so-called static radius where the gravitational attraction is balanced by the cosmic repulsion-it is demonstrated both in terms of the effective potential of the string motion and the basin boundary method reflecting its chaotic character, that a potential barrier exists along the static radius behind which no trapped oscillations may exist. The trapped states of the string loops, governed by the interplay of the gravitating mass M and the cosmic repulsion, are allowed only in Schwarzschild-de Sitter spacetimes with the cosmological parameter λ<λ_trap 0.00497. The trapped oscillations can extend close to the radius of photon circular orbit, down to r_mt 3.3M.

gr-qc↗