5,979 research outputs found
Precessing supermassive black hole binaries and dark energy measurements with LISA
Spin induced precessional modulations of gravitational wave signals from
supermassive black hole binaries can improve the estimation of luminosity
distance to the source by space based gravitational wave missions like the
Laser Interferometer Space Antenna (LISA). We study how this impacts the ablity
of LISA to do cosmology, specifically, to measure the dark energy equation of
state (EOS) parameter . Using the CDM model of cosmology, we show
that observations of precessing binaries by LISA, combined with a redshift
measurement, can improve the determination of up to an order of magnitude
with respect to the non precessing case depending on the masses, mass ratio and
the redshift.Comment: 4 pages, 4 figures, version accepted to PR
Probing the Brans-Dicke Gravitational Field by Cerenkov Radiation
The possibility that a charged particle propagating in a gravitational field
described by Brans-Dicke theory of gravity could emit Cerenkov radiation is
explored. This process is kinematically allowed depending on parameters
occurring in the theory. The Cerenkov effect disappears as the BD parameter
omega tends to inftinity, i.e. in the limit in which the Einstein theory is
recovered, giving a signature to probe the validity of the Brans-Dicke theory.Comment: 8 pages, no figure
Progress in Lunar Laser Ranging Tests of Relativistic Gravity
Analyses of laser ranges to the Moon provide increasingly stringent limits on
any violation of the Equivalence Principle (EP); they also enable several very
accurate tests of relativistic gravity. We report the results of our recent
analysis of Lunar Laser Ranging (LLR) data giving an EP test of \Delta
(M_G/M_I)_{EP} =(-1.0 +/- 1.4) x 10^{-13}. This result yields a Strong
Equivalence Principle (SEP) test of \Delta (M_G/M_I)_{SEP} =(-2.0 +/- 2.0) x
10^{-13}. Also, the corresponding SEP violation parameter \eta is (4.4 +/- 4.5)
x 10^{-4}, where \eta=4\beta-\gamma-3 and both \beta and \gamma are
parametrized post-Newtonian (PPN) parameters. Using the recent Cassini result
for the parameter \gamma, PPN parameter \beta is determined to be \beta-1=(1.2
+/- 1.1) x 10^{-4}. The geodetic precession test, expressed as a relative
deviation from general relativity, is K_{gp}=-0.0019 +/- 0.0064. The search for
a time variation in the gravitational constant results in \dot G/G=(4 +/- 9) x
10^{-13} yr^{-1}, consequently there is no evidence for local (~1AU) scale
expansion of the solar system.Comment: 4 pages, revtex4, minor changes made for publicatio
Time-delay and Doppler tests of the Lorentz symmetry of gravity
Modifications to the classic time-delay effect and Doppler shift in General
Relativity (GR) are studied in the context of the Lorentz-violating
Standard-Model Extension (SME). We derive the leading Lorentz-violating
corrections to the time-delay and Doppler shift signals, for a light ray
passing near a massive body. It is demonstrated that anisotropic coefficients
for Lorentz violation control a time-dependent behavior of these signals that
is qualitatively different from the conventional case in GR. Estimates of
sensitivities to gravity-sector coefficients in the SME are given for current
and future experiments, including the recent Cassini solar conjunction
experiment.Comment: 13 pages, 4 figures, references added, matches PRD versio
Constraining the evolutionary history of Newton's constant with gravitational wave observations
Space-borne gravitational wave detectors, such as the proposed Laser
Interferometer Space Antenna, are expected to observe black hole coalescences
to high redshift and with large signal-to-noise ratios, rendering their
gravitational waves ideal probes of fundamental physics. The promotion of
Newton's constant to a time-function introduces modifications to the binary's
binding energy and the gravitational wave luminosity, leading to corrections in
the chirping frequency. Such corrections propagate into the response function
and, given a gravitational wave observation, they allow for constraints on the
first time-derivative of Newton's constant at the time of merger. We find that
space-borne detectors could indeed place interesting constraints on this
quantity as a function of sky position and redshift, providing a
{\emph{constraint map}} over the entire range of redshifts where binary black
hole mergers are expected to occur. A LISA observation of an equal-mass
inspiral event with total redshifted mass of 10^5 solar masses for three years
should be able to measure at the time of merger to better than
10^(-11)/yr.Comment: 11 pages, 2 figures, replaced with version accepted for publication
in Phys. Rev. D
Coexistence of black holes and a long-range scalar field in cosmology
The exactly solvable scalar hairy black hole model (originated from the
modern high-energy theory) is proposed. It turns out that the existence of
black holes (BH) is strongly correlated to global scalar field, in a sense that
they mutually impose bounds upon their physical parameters like the BH mass
(lower bound) or the cosmological constant (upper bound). We consider the same
model also as a cosmological one and show that it agrees with recent
experimental data; additionally, it provides a unified quintessence-like
description of dark energy and dark matter.Comment: 4 pages, 4 figure
The Newtonian Limit of F(R) gravity
A general analytic procedure is developed to deal with the Newtonian limit of
gravity. A discussion comparing the Newtonian and the post-Newtonian
limit of these models is proposed in order to point out the differences between
the two approaches. We calculate the post-Newtonian parameters of such theories
without any redefinition of the degrees of freedom, in particular, without
adopting some scalar fields and without any change from Jordan to Einstein
frame. Considering the Taylor expansion of a generic theory, it is
possible to obtain general solutions in term of the metric coefficients up to
the third order of approximation. In particular, the solution relative to the
component gives a gravitational potential always corrected with
respect to the Newtonian one of the linear theory . Furthermore, we
show that the Birkhoff theorem is not a general result for -gravity since
time-dependent evolution for spherically symmetric solutions can be achieved
depending on the order of perturbations. Finally, we discuss the
post-Minkowskian limit and the emergence of massive gravitational wave
solutions.Comment: 16 page
Testing Alternative Theories of Gravity using LISA
We investigate the possible bounds which could be placed on alternative
theories of gravity using gravitational wave detection from inspiralling
compact binaries with the proposed LISA space interferometer. Specifically, we
estimate lower bounds on the coupling parameter \omega of scalar-tensor
theories of the Brans-Dicke type and on the Compton wavelength of the graviton
\lambda_g in hypothetical massive graviton theories. In these theories,
modifications of the gravitational radiation damping formulae or of the
propagation of the waves translate into a change in the phase evolution of the
observed gravitational waveform. We obtain the bounds through the technique of
matched filtering, employing the LISA Sensitivity Curve Generator (SCG),
available online. For a neutron star inspiralling into a 10^3 M_sun black hole
in the Virgo Cluster, in a two-year integration, we find a lower bound \omega >
3 * 10^5. For lower-mass black holes, the bound could be as large as 2 * 10^6.
The bound is independent of LISA arm length, but is inversely proportional to
the LISA position noise error. Lower bounds on the graviton Compton wavelength
ranging from 10^15 km to 5 * 10^16 km can be obtained from one-year
observations of massive binary black hole inspirals at cosmological distances
(3 Gpc), for masses ranging from 10^4 to 10^7 M_sun. For the highest-mass
systems (10^7 M_sun), the bound is proportional to (LISA arm length)^{1/2} and
to (LISA acceleration noise)^{-1/2}. For the others, the bound is independent
of these parameters because of the dominance of white-dwarf confusion noise in
the relevant part of the frequency spectrum. These bounds improve and extend
earlier work which used analytic formulae for the noise curves.Comment: 16 pages, 9 figures, submitted to Classical & Quantum Gravit
A Search for New Physics with the BEACON Mission
The primary objective of the Beyond Einstein Advanced Coherent Optical
Network (BEACON) mission is a search for new physics beyond general relativity
by measuring the curvature of relativistic space-time around Earth. This
curvature is characterized by the Eddington parameter \gamma -- the most
fundamental relativistic gravity parameter and a direct measure for the
presence of new physical interactions. BEACON will achieve an accuracy of 1 x
10^{-9} in measuring the parameter \gamma, thereby going a factor of 30,000
beyond the present best result involving the Cassini spacecraft. Secondary
mission objectives include: (i) a direct measurement of the "frame-dragging"
and geodetic precessions in the Earth's rotational gravitomagnetic field, to
0.05% and 0.03% accuracy correspondingly, (ii) first measurement of gravity's
non-linear effects on light and corresponding 2nd order spatial metric's
effects to 0.01% accuracy. BEACON will lead to robust advances in tests of
fundamental physics -- this mission could discover a violation or extension of
general relativity and/or reveal the presence of an additional long range
interaction in physics. BEACON will provide crucial information to separate
modern scalar-tensor theories of gravity from general relativity, probe
possible ways for gravity quantization, and test modern theories of
cosmological evolution.Comment: 8 pages, 2 figures, 2 table
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