184 research outputs found
Kerr-Gauss-Bonnet Black Holes: An Analytical Approximation
Gauss-Bonnet gravity provides one of the most promising frameworks to study
curvature corrections to the Einstein action in supersymmetric string theories,
while avoiding ghosts and keeping second order field equations. Although
Schwarzschild-type solutions for Gauss-Bonnet black holes have been known for
long, the Kerr-Gauss-Bonnet metric is missing. In this paper, a five
dimensional Gauss-Bonnet approximation is analytically derived for spinning
black holes and the related thermodynamical properties are briefly outlined.Comment: 5 pages, 1 figur
Global properties of dilatonic Gauss-Bonnet black holes
We study the phase space of the spherically symmetric solutions of Einstein
Gauss-Bonnet system nonminimally coupled to a scalar field and show that in
four dimensions the only regular black hole solutions are asymptotically flatComment: 12 pages, plain TeX; v.2: phase space is described in more detai
Probing neutrino mass hierarchies and with supernova neutrinos
We investigate the feasibility of probing the neutrino mass hierarchy and the
mixing angle with the neutrino burst from a future supernova. An
inverse power-law density with varying is adopted in the
analysis as the density profile of a typical core-collapse supernova. The
survival probabilities of and are shown to reduce to
two-dimensional functions of and . It is found that in the
parameter space, the 3D plots of the probability
functions exhibit highly non-trivial structures that are sensitive to the mass
hierarchy, the mixing angle , and the value of . The conditions
that lead to observable differences in the 3D plots are established. With the
uncertainty of considered, a qualitative analysis of the Earth matter
effect is also included.Comment: 16 pages, 3 figures. Ref [11] added, and some typos correcte
Transverse rotation of the momentary field distribution and the orbital angular momentum of a light beam
The transverse beam pattern, usually observed in experiment, is a result of
averaging the optical-frequency oscillations of the electromagnetic field
distributed over the beam cross section. An analytical criterion is derived
that these oscillations are coupled with a sort of rotation around the beam
axis. This criterion appears to be in direct relation with the usual definition
of the beam orbital angular momentum.Comment: 9 pages, 1 figure with animatio
Nature of singularities in anisotropic string cosmology
We study nature of singularities in anisotropic string-inspired cosmological
models in the presence of a Gauss-Bonnet term. We analyze two string gravity
models-- dilaton-driven and modulus-driven cases-- in the Bianchi type-I
background without an axion field. In both scenarios singularities can be
classified in two ways- the determinant singularity where the main determinant
of the system vanishes and the ordinary singularity where at least one of the
anisotropic expansion rates of the Universe diverges. In the dilaton case,
either of these singularities inevitably appears during the evolution of the
system. In the modulus case, nonsingular cosmological solutions exist both in
asymptotic past and future with determinant and D=2, respectively.
In both scenarios nonsingular trajectories in either future or past typically
meet the determinant singularity in past/future when the solutions are
singular, apart from the exceptional case where the sign of the time-derivative
of dilaton is negative. This implies that the determinant singularity may play
a crucial role to lead to singular solutions in an anisotropic background.Comment: 21 pages, 8 figure
Rotating light, OAM paradox and relativistic complex scalar field
Recent studies show that the angular momentum, both spin and orbital, of
rotating light beams possesses counter-intuitive characteristics. We present a
new approach to the question of orbital angular momentum of light based on the
complex massless scalar field representation of light. The covariant equation
for the scalar field is treated in rotating system using the general
relativistic framework. First we show the equivalence of the U(1) gauge current
for the scalar field with the Poynting vector continuity equation for paraxial
light, and then apply the formalism to the calculation of the orbital angular
momentum of rotating light beams. If the difference between the co-, contra-,
and physical quantities is properly accounted for there does not result any
paradox in the orbital angular momentum of rotating light. An artificial
analogue of the paradoxical situation could be constructed but it is wrong
within the present formalism. It is shown that the orbital angular momentum of
rotating beam comprising of modes with opposite azimuthal indices corresponds
to that of rigid rotation. A short review on the electromagnetism in
noninertial systems is presented to motivate a fully covariant Maxwell field
approach in rotating system to address the rotating light phenomenon.Comment: No figure
Do stringy corrections stabilize coloured black holes?
We consider hairy black hole solutions of Einstein-Yang-Mills-Dilaton theory,
coupled to a Gauss-Bonnet curvature term, and we study their stability under
small, spacetime-dependent perturbations. We demonstrate that the stringy
corrections do not remove the sphaleronic instabilities of the coloured black
holes with the number of unstable modes being equal to the number of nodes of
the background gauge function. In the gravitational sector, and in the limit of
an infinitely large horizon, the coloured black holes are also found to be
unstable. Similar behaviour is exhibited by the magnetically charged black
holes while the bulk of the neutral black holes are proven to be stable under
small, gauge-dependent perturbations. Finally, the electrically charged black
holes are found to be characterized only by the existence of a gravitational
sector of perturbations. As in the case of neutral black holes, we demonstrate
that for the bulk of electrically charged black holes no unstable modes arise
in this sector.Comment: 17 pages, Revtex, comments and a reference added, version to appear
in Physical Review
Dirac neutrino magnetic moment and a possible time evolution of the neutrino signal from a supernova
We analyze the influence of neutrino helicity conversion, ,
on the neutrino flux from a supernova caused by the interaction of the Dirac
neutrino magnetic moment with a magnetic field. We show that if the neutrino
has a magnetic moment in the interval and provided that a magnetic field of G exists in the supernova envelope, a peculiar kind of time evolution
of the neutrino signal from the supernova caused by the resonance transition
in the magnetic field of the envelope can appear. If a
magnetar with a poloidal magnetic field is formed in a supernova explosion,
then the neutrino signal could have a pulsating behavior, i.e., a kind of a
neutrino pulsar could be observed, when it rotates around an axis that does not
coincide with its magnetic moment and when the orientation of its rotation axis
is favourable for our observation.Comment: 9 pages, LaTeX, 2 EPS figures, based on the talk presented by A.V.
Kuznetsov at the XVI International Seminar Quarks'2010, Kolomna, Moscow
Region, June 6-12, 2010, to appear in the Proceeding
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