134 research outputs found
Effective field theory calculation of conservative binary dynamics at third post-Newtonian order
We reproduce the two-body gravitational conservative dynamics at third
post-Newtonian order for spin-less sources by using the effective field theory
methods for the gravitationally bound two-body system, proposed by Goldberger
and Rothstein. This result has been obtained by automatizing the computation of
Feynman amplitudes within a Mathematica algorithm, paving the way for
higher-order computations not yet performed by traditional methods.Comment: 24 pages, 6 figures. Typos corrected and references added in v2.
Typos corrected in v
Symmetry breaking aspects of the effective Lagrangian for quantum black holes
The physical excitations entering the effective Lagrangian for quantum black
holes are related to a Goldstone boson which is present in the Rindler limit
and is due to the spontaneous breaking of the translation symmetry of the
underlying Minkowski space. This physical interpretation, which closely
parallels similar well-known results for the effective stringlike description
of flux tubes in QCD, gives a physical insight into the problem of describing
the quantum degrees of freedom of black holes. It also suggests that the
recently suggested concept of 'black hole complementarity' emerges at the
effective Lagrangian level rather than at the fundamental level.Comment: 11 pages, Latex,1 figur
Multichannel matched filtering for spherical gravitational wave antennas
We study the performance of a multidimensional matched filter as a follow-up
module of the coherent method recently developed by two of us for the detection
of gravitational wave bursts by spherical resonant detectors. We have tested
this strategy on the same set of injections used for the coherent method and
found that the matched filter sensibly improves the determination of relevant
parameters as the arrival time, amplitude, central frequency and arrival
direction of the signal. The matched filter also improves the false alarm rate,
reducing it roughly by a factor of 3. The hierarchical structure of the whole
analysis pipeline allows to obtain these results without a significant increase
of the computation time.Comment: 11 pages, 4 figures, final version to be published on Classical and
Quantum Gravity as part of the Proceedings of GWDAW1
Bouncing pre-big bang on the brane
A regular bouncing universe is obtained in the context of a dilaton-gravity
brane world scenario. The scale factor starts in a contracting inflationary
phase both in the Einstein and in the string frame, it then undergoes a bounce
(due to interaction with the bulk Weyl tensor), and subsequently enters into a
decelerated expanding era. This graceful exit is obtained at low curvature and
low coupling, and without violating the Null Energy Condition.Comment: 16 pages, 3 figures; final version to be published on PRD. General
improvement of section II (better specification of the matter content on the
brane and discussion about the late time behavior), main results unchanged; 2
references adde
Events trigger generator for resonant spherical detectors of gravitational waves
We have set up and tested a pipeline for processing the data from a spherical
gravitational wave detector with six transducers. The algorithm exploits the
multichannel capability of the system and provides a list of candidate events
with their arrival direction. The analysis starts with the conversion of the
six detector outputs into the scalar and the five quadrupolar modes of the
sphere, which are proportional to the corresponding gravitational wave
spherical components. Event triggers are then generated by an adaptation of the
WaveBurst algorithm. Event validation and direction reconstruction are made by
cross-checking two methods of different inspiration: geometrical (lowest
eigenvalue) and probabilistic (maximum likelihood). The combination of the two
methods is able to keep substantially unaltered the efficiency and can reduce
drastically the detections of fake events (to less than ten per cent). We show
a quantitative test of these ideas by simulating the operation of the resonant
spherical detector miniGRAIL, whose planned sensitivity in its frequency band
(few hundred Hertz's around 3 kHz) is comparable with the present LIGO one.Comment: 14 pages, 8 figures. Version accepted for publication on CQG.
Proceedings of the 12th Gravitational Wave Data Analysis Worksho
On the "Causality Argument" in Bouncing Cosmologies
We exhibit a situation in which cosmological perturbations of astrophysical
relevance propagating through a bounce are affected in a scale-dependent way.
Involving only the evolution of a scalar field in a closed universe described
by general relativity, the model is consistent with causality. Such a specific
counter-example leads to the conclusion that imposing causality is not
sufficient to determine the spectrum of perturbations after a bounce provided
it is known before. We discuss consequences of this result for string motivated
scenarios.Comment: 4 pages, 1 figure, ReVTeX, to appear in Phys. Rev. Let
Combining chirp mass, luminosity distance and sky localisation from gravitational wave events to detect the cosmic dipole
A key test of the isotropy of the Universe on large scales consists in
comparing the dipole in the Cosmic Microwave Background (CMB) temperature with
the dipole in the distribution of sources at low redshift. Current analyses
find a dipole in the number counts of quasars and radio sources that is 2-5
times larger than expected from the CMB, leading to a tension reaching
5. In this paper, we derive a consistent framework to measure the
dipole independently from gravitational wave (GW) detections. We exploit the
fact that the observer velocity does not only change the distribution of events
in the sky, but also the luminosity distance and redshifted chirp mass, that
can be extracted from the GW waveform. We show that the estimator with higher
signal-to-noise ratio is the dipole in the chirp mass measured from a
population of binary neutron stars. Combining all estimators (accounting for
their covariance) improves the detectability of the dipole by 30-50 percent
compared to number counting of binary black holes alone. We find that a few
events are necessary to detect a dipole consistent with the CMB one,
whereas if the dipole is as large as predicted by radio sources, it will
already be detectable with events, which would correspond to a single
year of observation with next generation GW detectors. GW sources provide
therefore a robust and independent way of testing the isotropy of the Universe.Comment: 17 pages, 11 figues, submitted to MNRA
Aligned Spins: Orbital Elements, Decaying Orbits, and Last Stable Circular Orbit to high post-Newtonian Orders
In this article the quasi-Keplerian parameterisation for the case that spins
and orbital angular momentum in a compact binary system are aligned or
anti-aligned with the orbital angular momentum vector is extended to 3PN
point-mass, next-to-next-to-leading order spin-orbit, next-to-next-to-leading
order spin(1)-spin(2), and next-to-leading order spin-squared dynamics in the
conservative regime. In a further step, we use the expressions for the
radiative multipole moments with spin to leading order linear and quadratic in
both spins to compute radiation losses of the orbital binding energy and
angular momentum. Orbital averaged expressions for the decay of energy and
eccentricity are provided. An expression for the last stable circular orbit is
given in terms of the angular velocity type variable .Comment: 30 pages, 2 figures, v2: update to match published versio
A Solution to the Graceful Exit Problem in Pre-Big Bang Cosmology
We examine the string cosmology equations with a dilaton potential in the
context of the Pre-Big Bang Scenario with the desired scale factor duality, and
give a generic algorithm for obtaining solutions with appropriate evolutionary
properties. This enables us to find pre-big bang type solutions with suitable
dilaton behaviour that are regular at , thereby solving the graceful exit
problem. However to avoid fine tuning of initial data, an `exotic' equation of
state is needed that relates the fluid properties to the dilaton field. We
discuss why such an equation of state should be required for reliable dilaton
behaviour at late times.Comment: 16 pages LaTeX, 5 figures. To appear in Physical Review
- …