429 research outputs found
An Effective Search Method for Gravitational Ringing of Black Holes
We develop a search method for gravitational ringing of black holes. The
gravitational ringing is due to complex frequency modes called the quasi-normal
modes that are excited when a black hole geometry is perturbed. The detection
of it will be a direct confirmation of the existence of a black hole. Assuming
that the ringdown waves are dominated by the fundamental mode with least
imaginary part, we consider matched filtering and develop an optimal method to
search for the ringdown waves that have damped sinusoidal wave forms.
When we use the matched filtering method, the data analysis with a lot of
templates required. Here we have to ensure a proper match between the filter as
a template and the real wave. It is necessary to keep the detection efficiency
as high as possible under limited computational costs.
First, we consider the white noise case for which the matched filtering can
be studied analytically. We construct an efficient method for tiling the
template space. Then, using a fitting curve of the TAMA300 DT6 noise spectrum,
we numerically consider the case of colored noise. We find our tiling method
developed for the white noise case is still valid even if the noise is colored.Comment: 17 pages, 9 figures. Accepted to Phys. Rev. D, Note correction to Eq.
(3-25), A few comments added and minor typos correcte
Simple sufficient conditions for the generalized covariant entropy bound
The generalized covariant entropy bound is the conjecture that the entropy of
the matter present on any non-expanding null hypersurface L will not exceed the
difference between the areas, in Planck units, of the initial and final spatial
2-surfaces bounding L. The generalized Bekenstein bound is a special case which
states that the entropy of a weakly gravitating isolated matter system will not
exceed the product of its mass and its width. Here we show that both bounds can
be derived directly from the following phenomenological assumptions: that
entropy can be computed by integrating an entropy current which vanishes on the
initial boundary and whose gradient is bounded by the energy density. Though we
note that any local description of entropy has intrinsic limitations, we argue
that our assumptions apply in a wide regime. We closely follow the framework of
an earlier derivation, but our assumptions take a simpler form, making their
validity more transparent in some examples.Comment: 7 pages, revte
Quantum inequalities in two dimensional curved spacetimes
We generalize a result of Vollick constraining the possible behaviors of the
renormalized expected stress-energy tensor of a free massless scalar field in
two dimensional spacetimes that are globally conformal to Minkowski spacetime.
Vollick derived a lower bound for the energy density measured by a static
observer in a static spacetime, averaged with respect to the observers proper
time by integrating against a smearing function. Here we extend the result to
arbitrary curves in non-static spacetimes. The proof, like Vollick's proof, is
based on conformal transformations and the use of our earlier optimal bound in
flat Minkowski spacetime. The existence of such a quantum inequality was
previously established by Fewster.Comment: revtex 4, 5 pages, no figures, submitted to Phys. Rev. D. Minor
correction
A Linear-Nonlinear Formulation of Einstein Equations for the Two-Body Problem in General Relativity
A formulation of Einstein equations is presented that could yield advantages
in the study of collisions of binary compact objects during regimes between
linear-nonlinear transitions. The key idea behind this formulation is a
separation of the dynamical variables into i) a fixed conformal 3-geometry, ii)
a conformal factor possessing nonlinear dynamics and iii) transverse-traceless
perturbations of the conformal 3-geometry.Comment: 7 pages, no figure
Gravitational waves from eccentric compact binaries: Reduction in signal-to-noise ratio due to nonoptimal signal processing
Inspiraling compact binaries have been identified as one of the most
promising sources of gravitational waves for interferometric detectors. Most of
these binaries are expected to have circularized by the time their
gravitational waves enter the instrument's frequency band. However, the
possibility that some of the binaries might still possess a significant
eccentricity is not excluded. We imagine a situation in which eccentric signals
are received by the detector but not explicitly searched for in the data
analysis, which uses exclusively circular waveforms as matched filters. We
ascertain the likelihood that these filters, though not optimal, will
nevertheless be successful at capturing the eccentric signals. We do this by
computing the loss in signal-to-noise ratio incurred when searching for
eccentric signals with those nonoptimal filters. We show that for a binary
system of a given total mass, this loss increases with increasing eccentricity.
We show also that for a given eccentricity, the loss decreases as the total
mass is increased.Comment: 14 pages, 4 figures, ReVTeX; minor changes made after referee's
comment
A Quantum Bousso Bound
The Bousso bound requires that one quarter the area of a closed codimension
two spacelike surface exceeds the entropy flux across a certain lightsheet
terminating on the surface. The bound can be violated by quantum effects such
as Hawking radiation. It is proposed that at the quantum level the bound be
modified by adding to the area the quantum entanglement entropy across the
surface. The validity of this quantum Bousso bound is proven in a
two-dimensional large N dilaton gravity theory.Comment: 17 page
Quantum inequalities for the free Rarita-Schwinger fields in flat spacetime
Using the methods developed by Fewster and colleagues, we derive a quantum
inequality for the free massive spin- Rarita-Schwinger fields in
the four dimensional Minkowski spacetime. Our quantum inequality bound for the
Rarita-Schwinger fields is weaker, by a factor of 2, than that for the
spin- Dirac fields. This fact along with other quantum inequalities
obtained by various other authors for the fields of integer spin (bosonic
fields) using similar methods lead us to conjecture that, in the flat
spacetime, separately for bosonic and fermionic fields, the quantum inequality
bound gets weaker as the the number of degrees of freedom of the field
increases. A plausible physical reason might be that the more the number of
field degrees of freedom, the more freedom one has to create negative energy,
therefore, the weaker the quantum inequality bound.Comment: Revtex, 11 pages, to appear in PR
A Comparison of search templates for gravitational waves from binary inspiral
We compare the performances of the templates defined by three different types
of approaches: traditional post-Newtonian templates (Taylor-approximants),
``resummed'' post-Newtonian templates assuming the adiabatic approximation and
stopping before the plunge (P-approximants), and further ``resummed''
post-Newtonian templates going beyond the adiabatic approximation and
incorporating the plunge with its transition from the inspiral
(Effective-one-body approximants). The signal to noise ratio is significantly
enhanced (mainly because of the inclusion of the plunge signal) by using these
new effective-one-body templates relative to the usual post-Newtonian ones for
binary masses greater than , the most likely sources for initial
laser interferometers. Independently of the question of the plunge signal, the
comparison of the various templates confirms the usefulness of using
resummation methods. The paper also summarizes the key elements of the
construction of various templates and thus can serve as a resource for those
involved in writing inspiral search software.Comment: eta-dependent tail terms corrected after related errata by Blanchet
(2005
Flat space physics from holography
We point out that aspects of quantum mechanics can be derived from the
holographic principle, using only a perturbative limit of classical general
relativity. In flat space, the covariant entropy bound reduces to the
Bekenstein bound. The latter does not contain Newton's constant and cannot
operate via gravitational backreaction. Instead, it is protected by - and in
this sense, predicts - the Heisenberg uncertainty principle.Comment: 11 pages, 3 figures; v2: minor correction
Palatini approach to 1/R gravity and its implications to the late Universe
By applying the Palatini approach to the 1/R-gravity model it is possible to
explain the present accelerated expansion of the Universe. Investigation of the
late Universe limiting case shows that: (i) due to the curvature effects the
energy-momentum tensor of the matter field is not covariantly conserved; (ii)
however, it is possible to reinterpret the curvature corrections as sources of
the gravitational field, by defining a modified energy-momentum tensor; (iii)
with the adoption of this modified energy-momentum tensor the Einstein's field
equations are recovered with two main modifications: the first one is the
weakening of the gravitational effects of matter whereas the second is the
emergence of an effective varying "cosmological constant"; (iv) there is a
transition in the evolution of the cosmic scale factor from a power-law scaling
to an asymptotically exponential scaling ; (v) the energy density of the matter field scales as ; (vi) the present age of the Universe and the
decelerated-accelerated transition redshift are smaller than the corresponding
ones in the CDM model.Comment: 5 pages and 2 figures. Accepted in PR
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