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 {\lambda}=1/3{\Lambda}M^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 {\Lambda}. 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 {\lambda}<{\lambda}_trap 0.00497. The trapped oscillations can extend close to the radius of photon circular orbit, down to r_mt 3.3M.Comment: 21 pages, 22 figure

Influence of the relict cosmological constant on accretion discs

Surprisingly, the relict cosmological constant has a crucial influence on properties of accretion discs orbiting black holes in quasars and active galactic nuclei. We show it by considering basic properties of both the geometrically thin and thick accretion discs in the Kerr-de Sitter black-hole (naked-singularity) spacetimes. Both thin and thick discs must have an outer edge allowing outflow of matter into the outer space, located nearby the so called static radius, where the gravitational attraction of a black hole is balanced by the cosmological repulsion. Jets produced by thick discs can be significantly collimated after crossing the static radius. Extension of discs in quasars is comparable with extension of the associated galaxies, indicating a possibility that the relict cosmological constant puts an upper limit on extension of galaxies.Comment: 15 pages, 4 figures, invited pape

Forces in Kerr spacetimes with a repulsive cosmological constant

Forces defined in the framework of optical reference geometry are introduced in the case of stationary and axially symmetric Kerr black-hole and naked-singularity spacetimes with a repulsive cosmological constant. Properties of the forces acting on test particles moving along circular orbits in the equatorial plane are discussed, whereas it is shown where the gravitational force vanishes and changes its orientation and where the centrifugal force vanishes and changes its orientation independently of the velocity of test particles related to the optical geometry; the Coriolis force does not vanish for the velocity being non-zero. The spacetimes are classified according to the number of circular orbits where the gravitational and centrifugal forces vanish

Fluctuations of CMBR in accelerating universe

The influence of the observed relict vacuum energy on the fluctuations of CMBR going through cosmological matter condensations is studied in the framework of the Einstein-Strauss-de Sitter vakuola model. It is shown that refraction of light at the matching surface of the vakuola and the expanding Friedman universe can be very important during accelerated expansion of the universe, when the velocity of the matching surface relative to static Schwarzchildian observers becomes relativistic. Relevance of the refraction effect for the temperature fluctuations of CMBR is given in terms of the redshift and the angular extension of the fluctuating region

Are eikonal quasinormal modes linked to the unstable circular null geodesics?

In Phys. Rev. D 79, 064016 (2009) it was claimed that quasinormal modes which any stationary, spherically symmetric and asymptotically flat black hole emits in the eikonal regime are determined by the parameters of the circular null geodesic: the real and imaginary parts of the quasinormal mode are multiples of the frequency and instability timescale of the circular null geodesics respectively. We shall consider asymptotically flat black hole in the Einstein-Lovelock theory, find analytical expressions for gravitational quasinormal modes in the eikonal regime and analyze the null geodesics. Comparison of the both phenomena shows that the expected link between the null geodesics and quasinormal modes is violated in the Einstein-Lovelock theory. Nevertheless, the correspondence exists for a number of other cases and here we formulate its actual limits.Comment: 8 pages, revtex, refereed version, accepted for publication in Physics Letters