136 research outputs found
The Thermodynamics of Kaluza-Klein Black Hole/Bubble Chains
A Killing bubble is a minimal surface that arises as the fixed surface of a
spacelike Killing field. We compute the bubble contributions to the Smarr
relations and the mass and tension first laws for spacetimes containing both
black holes and Killing bubbles. The resulting relations display an interesting
interchange symmetry between the properties of black hole horizons and those of
KK bubbles. This interchange symmetry reflects the underlying relation between
static bubbles and black holes under double analytic continuation of the time
and Kaluza-Klein directions. The thermodynamics of bubbles involve a
geometrical quantity that we call the bubble surface gravity, which we show has
several properties in common with the black hole surface gravity.Comment: 20 pages, 1 figur
Doppler peaks from active perturbations
We examine how the qualitative structure of the Doppler peaks in the angular
power spectrum of the cosmic microwave anisotropy depends on the fundamental
nature of the perturbations which produced them. The formalism of Hu and
Sugiyama is extended to treat models with cosmic defects. We discuss how
perturbations can be ``active'' or ``passive'' and ``incoherent'' or
``coherent'', and show how causality and scale invariance play rather different
roles in these various cases. We find that the existence of secondary Doppler
peaks and the rough placing of the primary peak unambiguously reflect these
basic properties.Comment: uufile, 8pages, 3 figures. Now available at
http://euclid.tp.ph/Papers/index.html; Changes: URL added, Eqn. (8) expanded,
grant numbers include
Dynamics of the DBI Spike Soliton
We compare oscillations of a fundamental string ending on a D3-brane in two
different settings: (1) a test-string radially threading the horizon of an
extremal black D3-brane and (2) the spike soliton of the DBI effective action
for a D3-brane. Previous work has shown that overall transverse modes of the
test-string appear as l=0 modes of the transverse scalar fields of the DBI
system. We identify DBI world-volume degrees of freedom that have dynamics
matching those of the test-string relative transverse modes. We show that there
is a map, resembling T-duality, between relative and overall transverse modes
for the test-string that interchanges Neumann and Dirichlet boundary conditions
and implies equality of the absorption coefficients for both modes. We give
general solutions to the overall and relative transverse parts of the DBI
coupled gauge and scalar system and calculate absorption coefficients for the
higher angular momentum modes in the low frequency limit. We find that there is
a nonzero amplitude for l>0 modes to travel out to infinity along the spike,
demonstrating that the spike remains effectively 3+1-dimensional.Comment: 15 pages, 1 figur
Formation of Five-Dimensional String Solutions from the Gravitational Collapse
We study the formation of five-dimensional string solutions including the
Gregory-Laflamme (GL) black string, the Kaluza-Klein (KK) bubble, and the
geometry with a naked singularity from the gravitational collapse. The interior
solutions of five-dimensional Einstein equations describe collapsing
non-isotropic matter clouds. It is shown that the matter cloud always forms the
GL black string solution while the KK bubble solution cannot be formed. The
numerical study seems to suggest that the collapsing matter forms the
geometries with timelike naked curvature singularities, which should be taken
cautiously as the general relativity is not reliable in the strong curvature
regime.Comment: 17 pages, 10 figures, LaTeX, to appear in Class. Quant. Grav., a
appendix and some discussions added, title change
Thermodynamics of Squashed Kaluza-Klein Black Holes and Black Strings -- A Comparison of Reference Backgrounds --
We investigate thermodynamics constructed on different background reference
spacetimes for squashed Kaluza-Klein (SqKK) black hole and electrically charged
black string in five-dimensional Einstein-Maxwell system. Two spacetimes are
possible to be reference spacetimes giving finite gravitational classical
actions: one is four-dimensional Minkowski times a circle and the other is the
KK monopole. The boundary of the SqKK black hole can not be matched perfectly
to that of the former reference spacetime because of the difference in
topology. However, the resultant classical action coincides with that
calculated by the counterterm subtraction scheme. The boundary of the KK
monopole has the same topology with that of the SqKK black hole and can be
matched to the boundary of the black hole perfectly. The resultant action takes
different value from the result given by using the former reference spacetime.
After a brief review of thermodynamic quantities of the black hole solutions,
we calculate thermodynamic potentials relevant for several thermodynamic
environments. The most stable state is different for each environment: For
example, the KK monopole is the most stable state in isothermal environment
with fixed gravitational tension. On the other hand, when the size of the
extra-dimension is fixed, the Minkowski times a circle is the most stable. It
is shown that these two spacetimes can be reference spacetimes of the
five-dimensional black string.Comment: 28 pages; references added, typo corrected;version accepted for
publication in Class. Quantum Gra
Adiabatic Gravitational Perturbation During Reheating
We study the possibilities of parametric amplification of the gravitational
perturbation during reheating in single-field inflation models. Our result
shows that there is no additional growth of the super-horizon modes beyond the
usual predictions.Comment: Refs added; New version to appear in PR
Relativistic conservation laws and integral constraints for large cosmological perturbations
For every mapping of a perturbed spacetime onto a background and with any
vector field we construct a conserved covariant vector density ,
which is the divergence of a covariant antisymmetric tensor density, a
"superpotential". is linear in the energy-momentum tensor
perturbations of matter, which may be large; does not contain the
second order derivatives of the perturbed metric. The superpotential is
identically zero when perturbations are absent.
By integrating conserved vectors over a part \Si of a hypersurface of
the background, which spans a two-surface \di\Si, we obtain integral
relations between, on the one hand, initial data of the perturbed metric
components and the energy-momentum perturbations on \Si and, on the other
hand, the boundary values on \di\Si. We show that there are as many such
integral relations as there are different mappings, 's, \Si's and
\di\Si's. For given boundary values on \di\Si, the integral relations may
be interpreted as integral constraints (e.g., those of Traschen) on local
initial data including the energy-momentum perturbations. Conservation laws
expressed in terms of Killing fields \Bar\xi of the background become
"physical" conservation laws.
In cosmology, to each mapping of the time axis of a Robertson-Walker space on
a de Sitter space with the same spatial topology there correspond ten
conservation laws. The conformal mapping leads to a straightforward
generalization of conservation laws in flat spacetimes. Other mappings are also
considered. ...Comment: This paper, published 7 years ago, was found useful by some
researchers but originally was not put on the gr-qc website. Now it has been
retyped with very minor changes: few wordings have been modified and several
misprints occurring in the printed version correcte
Polarization Correlations in Pair Production from Charged and Neutral Strings
Polarization correlations of pair productions from charged and
neutral Nambu strings are investigated, via photon and graviton emissions,
respectively and explicit expressions for their corresponding probabilities are
derived and found to be \textit{speed} dependent. The strings are taken to be
circularly oscillating closed strings, as perhaps the simplest solution of the
Nambu action. In the extreme relativistic case, these probabilities coincide,
but, in general, are different, and such inquiries, in principle, indicate
whether the string is charged or uncharged. It is remarkable that these
dynamical relativistic quantum field theory calculations lead to a clear
violation of Local Hidden Variables theories.Comment: 6 pages, no figure, LaTeX with ws-mpla.cl
Enthalpy and the Mechanics of AdS Black Holes
We present geometric derivations of the Smarr formula for static AdS black
holes and an expanded first law that includes variations in the cosmological
constant. These two results are further related by a scaling argument based on
Euler's theorem. The key new ingredient in the constructions is a two-form
potential for the static Killing field. Surface integrals of the Killing
potential determine the coefficient of the variation of the cosmological
constant in the first law. This coefficient is proportional to a finite,
effective volume for the region outside the AdS black hole horizon, which can
also be interpreted as minus the volume excluded from a spatial slice by the
black hole horizon. This effective volume also contributes to the Smarr
formula. Since the cosmological constant is naturally thought of as a pressure,
the new term in the first law has the form of effective volume times change in
pressure that arises in the variation of the enthalpy in classical
thermodynamics. This and related arguments suggest that the mass of an AdS
black hole should be interpreted as the enthalpy of the spacetime.Comment: 21 pages; v2 references adde
On generation of metric perturbations during preheating
We consider the generation of the scalar mode of the metric perturbations
during preheating stage in a two field model with the potential . We discuss two possible
sources of such perturbations: a) due to the coupling between the perturbation
of the matter field and the background part of the matter field
, b) due to non-linear fluctuations in a condensate of
``particles'' of the field . Both types of the metric perturbations are
assumed to be small, and estimated using the linear theory of the metric
perturbations. We estimate analytically the upper limit of the amplitude of the
metric perturbations for all scales in the limit of so-called broad resonance,
and show that the large scale metric perturbations are very small, and taking
them into account does not influence the standard picture of the production of
the metric perturbations in inflationary scenario.Comment: This version is to be published in PRD, new references added and
typos correcte
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