29 research outputs found
Wave equations for the perturbations of a charged black hole
A pair of simple wave equations is presented for the symmetric gravitational
and electromagnetic perturbations of a charged black hole. One of the equations
is uncoupled, and the other has a source term given by the solution of the
first equation. The derivation is presented in full detail for either axially
symmetric or stationary perturbations, and is quite straightforward. This
result is expected to have important applications in astrophysical models.Comment: 4 page
Linearized gravity and gauge conditions
In this paper we consider the field equations for linearized gravity and
other integer spin fields on the Kerr spacetime, and more generally on
spacetimes of Petrov type D. We give a derivation, using the GHP formalism, of
decoupled field equations for the linearized Weyl scalars for all spin weights
and identify the gauge source functions occuring in these. For the spin weight
0 Weyl scalar, imposing a generalized harmonic coordinate gauge yields a
generalization of the Regge-Wheeler equation. Specializing to the Schwarzschild
case, we derive the gauge invariant Regge-Wheeler and Zerilli equation directly
from the equation for the spin 0 scalar.Comment: 24 pages, corresponds to published versio
Electromagnetic waves in NUT space: Solutions to the Maxwell equations
In this paper, using the Newman-Penrose formalism, we find the Maxwell
equations in NUT space and after separation into angular and radial components
solve them analytically. All the angular equations are solved in terms of
Jaccobi polynomials. The radial equations are transformed into Hypergeometric
and Heun's equations with the right hand sides including terms of different
order in the frequency of the perturbation which allow solutions in the
expansion of this parameter.Comment: 19 pages, Revtex format, Minor changes including an extention of the
discussion and typos correction, (Extended version of the article presented
to the GR16 conference, July 15-21 2001, Durban, South Africa
Classical moduli hair
We extend existing treatments of black hole solutions in String Gravity to
include moduli fields. We compute the external moduli and dilaton hair, as well
as of their associated axions,to in the framework of the loop
corrected superstring effective action for a Kerr-Newman black hole background.Comment: 11 pages,LaTex file,no figure
On the absence of scalar hair for charged rotating blackholes in non minimally coupled theories
In this work we check the validity of the no scalar hair theorem in charged
axisymmetric stationary black holes for a wide class of scalar tensor theories.Comment: Revtex style, 11 pages, major rivisions done, appendix added, title
change
Highly Damped Quasinormal Modes of Kerr Black Holes: A Complete Numerical Investigation
We compute for the first time very highly damped quasinormal modes of the
(rotating) Kerr black hole. Our numerical technique is based on a decoupling of
the radial and angular equations, performed using a large-frequency expansion
for the angular separation constant_{s}A_{l m}. This allows us to go much
further in overtone number than ever before. We find that the real part of the
quasinormal frequencies approaches a non-zero constant value which does not
depend on the spin s of the perturbing field and on the angular index l:
\omega_R=m\varpi(a). We numerically compute \varpi(a). Leading-order
corrections to the asymptotic frequency are likely to be of order 1/\omega_I.
The imaginary part grows without bound, the spacing between consecutive modes
being a monotonic function of a.Comment: 5 pages, 3 figure
Cosmological test of the Yilmaz theory of gravity
We test the Yilmaz theory of gravitation by working out the corresponding
Friedmann-type equations generated by assuming the Friedmann-Robertson-Walker
cosmological metrics. In the case that space is flat the theory is consistent
only with either a completely empty universe or a negative energy vacuum that
decays to produce a constant density of matter. In both cases the total energy
remains zero at all times, and in the latter case the acceleration of the
expansion is always negative. To obtain a more flexible and potentially more
realistic cosmology, the equation of state relating the pressure and energy
density of the matter creation process must be different from the vacuum, as
for example is the case in the steady-state models of Gold, Bondi, Hoyle and
others. The theory does not support the cosmological principle for curved space
K =/= 0 cosmological metrics
Collapse to Black Holes in Brans-Dicke Theory: II. Comparison with General Relativity
We discuss a number of long-standing theoretical questions about collapse to
black holes in the Brans-Dicke theory of gravitation. Using a new numerical
code, we show that Oppenheimer-Snyder collapse in this theory produces black
holes that are identical to those of general relativity in final equilibrium,
but are quite different from those of general relativity during dynamical
evolution. We find that there are epochs during which the apparent horizon of
such a black hole passes {\it outside\/} the event horizon, and that the
surface area of the event horizon {\it decreases\/} with time. This behavior is
possible because theorems which prove otherwise assume for
all null vectors . We show that dynamical spacetimes in Brans-Dicke theory
can violate this inequality, even in vacuum, for any value of .Comment: 24 pages including figures, uuencoded gz-compressed postscript,
Submitted to Phys Rev
Black Holes at the LHC
In these two lectures, we will address the topic of the creation of small
black holes during particle collisions in a ground-based accelerator, such as
LHC, in the context of a higher-dimensional theory. We will cover the main
assumptions, criteria and estimates for their creation, and we will discuss
their properties after their formation. The most important observable effect
associated with their creation is likely to be the emission of Hawking
radiation during their evaporation process. After presenting the mathematical
formalism for its study, we will review the current results for the emission of
particles both on the brane and in the bulk. We will finish with a discussion
of the methodology that will be used to study these spectra, and the observable
signatures that will help us identify the black-hole events.Comment: 37 pages, 14 figures, lectures presented in the 4th Aegean Summer
School on Black Holes, 17-22 September 2007, Lesvos, Greece, typos corrected,
comments and references adde
Hawking Radiation from Higher-Dimensional Black Holes
We review the quantum field theory description of Hawking radiation from evaporating black holes and summarize what is known about Hawking radiation from black holes in more than four space-time dimensions. In the context of the Large Extra Dimensions scenario, we present the theoretical formalism for all types of emitted fields and a selection of results on the radiation spectra. A detailed analysis of the Hawking fluxes in this case is essential for modelling the evaporation of higher-dimensional black holes at the LHC, whose creation is predicted by low-energy models of quantum gravity. We discuss the status of the quest for black-hole solutions in the context of the Randall-Sundrum brane-world model and, in the absence of an exact metric, we review what is known about Hawking radiation from such black holes