12 research outputs found
Quantum corrections to the noncommutative kink
We calculate quantum corrections to the mass of noncommutative phi^4 kink in
(1+1) dimensions for intermediate and large values of the noncommutativity
parameter theta. All one-loop divergences are removed by a mass renormalization
(which is different from the one required in the topologically trivial sector).
For large theta quantum corrections to the mass grow linearly with theta
signaling about possible break down of the perturbative expansion.Comment: 18 pages, v2: minor change
Analytical treatment of SUSY Quasi-normal modes in a non-rotating Schwarzschild black hole
We use the Fock-Ivanenko formalism to obtain the Dirac equation which
describes the interaction of a massless 1/2-spin neutral fermion with a
gravitational field around a Schwarzschild black hole (BH). We obtain
approximated analytical solutions for the eigenvalues of the energy
(quasi-normal frequencies) and their corresponding eigenstates (quasi-normal
states). The interesting result is that all the excited states [and their
supersymmetric (SUSY) partners] have a purely imaginary frequency, which can be
expressed in terms of the Hawking temperature. Furthermore, as one expects for
SUSY Hamiltonians, the isolated bottom state has a real null energy eigenvalue.Comment: Version to be published in European Physical Journal
Electromagnetic Fields of Slowly Rotating Compact Magnetized Stars in Braneworld
We study the structure of electromagnetic field of slowly rotating magnetized
star in a Randall-Sundrum II type braneworld. The star is modeled as a sphere
consisting of perfect highly magnetized fluid with infinite conductivity and
frozen-in dipolar magnetic field. Maxwell's equations for the external magnetic
field of the star in the braneworld are analytically solved in approximation of
small distance from the surface of the star. We have also found numerical
solution for the electric field outside the rotating magnetized neutron star in
the braneworld in dependence on brane tension. The influence of brane tension
on the electromagnetic energy losses of the rotating magnetized star is
underlined. Obtained "brane" corrections are shown to be relevant and have
non-negligible values. In comparison with astrophysical observations on pulsars
spindown data they may provide an evidence for the brane tension and, thus,
serve as a test for the braneworld model of the Universe.Comment: 11 pages, 5 figure
On Born approximation in black hole scattering
A massless field propagating on spherically symmetric black hole metrics such
as the Schwarzschild, Reissner-Nordstr\"{o}m and Reissner-Nordstr\"{o}m-de
Sitter backgrounds is considered. In particular, explicit formulae in terms of
transcendental functions for the scattering of massless scalar particles off
black holes are derived within a Born approximation. It is shown that the
conditions on the existence of the Born integral forbid a straightforward
extraction of the quasi normal modes using the Born approximation for the
scattering amplitude. Such a method has been used in literature. We suggest a
novel, well defined method, to extract the large imaginary part of quasinormal
modes via the Coulomb-like phase shift. Furthermore, we compare the numerically
evaluated exact scattering amplitude with the Born one to find that the
approximation is not very useful for the scattering of massless scalar,
electromagnetic as well as gravitational waves from black holes
Thermodynamics and classification of cosmological models in the Horava-Lifshitz theory of gravity
We study thermodynamics of cosmological models in the Horava-Lifshitz theory
of gravity, and systematically investigate the evolution of the universe filled
with a perfect fluid that has the equation of state , where and
denote, respectively, the pressure and energy density of the fluid, and
is an arbitrary real constant. Depending on specific values of the free
parameters involved in the models, we classify all of them into various cases.
In each case the main properties of the evolution are studied in detail,
including the periods of deceleration and/or acceleration, and the existence of
big bang, big crunch, and big rip singularities. We pay particular attention on
models that may give rise to a bouncing universe.Comment: revtex4, 21 figures. New references added & some changes made in
Introduction. Version to appear in JCA
Analytical study of superradiant instability of the five-dimensional Kerr–Gödel black hole
We present an analytical study of superradiant instability of rotating
asymptotically G\"{o}del black hole (Kerr-G\"{o}del black hole) in
five-dimensional minimal supergravity theory. By employing the matched
asymptotic expansion method to solve Klein-Gordon equation of scalar field
perturbation, we show that the complex parts of quasinormal frequencies are
positive in the regime of superradiance. This implies the growing instability
of superradiant modes. The reason for this kind of instability is the Dirichlet
boundary condition at asymptotic infinity, which is similar to that of rotating
black holes in anti-de Sitter (AdS) spacetime.Comment: 16 pages, no figure, some disscusion adde
Quasinormal modes, stability analysis and absorption cross section for 4-dimensional topological Lifshitz black hole
We study scalar perturbations in the background of a Topological Lifshitz
black hole in four dimensions. We compute analytically the quasinormal modes
and from these modes we show that Topological Lifshitz black hole is stable. On
the other hand, we compute the reflection and transmission coefficients and the
absorption cross section and we show that there is a range of modes with high
angular momentum which contributes to the absorption cross section in the low
frequency limit. Furthermore, in this limit, we show that the absorption cross
section decreases if the scalar field mass increases, for a real scalar field
mass.Comment: Version accepted for publication in EJP