227 research outputs found
Galactic Binary Gravitational Wave Noise within LISA Frequency Band
Gravitational wave noise associated with unresolved binary stars in the
Galaxy is studied with the special aim of determining the upper frequency at
which it stops to contribute at the rms noise level of the proposed space-born
interferometer (LISA). The upper limit to this background is derived from the
statistics of SN Ia explosions, part of which can be triggered by binary white
dwarf coalescences. The upper limiting frequency at which binary stochastic
noise crosses LISA rms sensitivity is found to lie within the range 0.03-0.07
Hz, depending on the galactic binary white dwarf coalescence rate. To be
reliably detectable by LISA, the energy density of relic cosmological
background per logarithmic frequency interval should be
Omega_{GW}h_{100}^2>10^{-8} at f>0.03 Hz.Comment: 16 pages with 1 eps figure, aasms4.sty, to appear in the ApJ vol. 494
February 20, 1998 issu
On the road to discovery of relic gravitational waves: The TE and BB Correlations in the cosmic microwave background radiation
The detection of primordial gravitational waves is one of the biggest
challenges of the present time. The existing (Wilkinson Microwave Anisotropy
Probe) observations are helpful on the road to this goal, and the forthcoming
experiments (Planck) are likely to complete this mission. We show that the
5-year Wilkinson Microwave Anisotropy Probe data contains a hint of the
presence of gravitational wave contribution. In terms of the parameter ,
which gives the ratio of contributions from gravitational waves and density
perturbations to the temperature quadrupole, the best-fit model produced
. Because of large residual noises, the uncertainty of this
determination is still large, and it easily includes the R=0 hypothesis.
However, the uncertainty will be strongly reduced in the forthcoming
observations which are more sensitive. We numerically simulated the Planck data
and concluded that the relic gravitational waves with will be present
at a better than 3 level in the observational channel, and at a
better than 2 level in the `realistic' channel. The balloon-borne
and ground-based observations may provide a healthy competition to Planck in
some parts of the lower- spectrum.Comment: 39 pages, including 23 figures. Modifications and clarifications in
response to referees' comments have been added. Includes the final
corrections made at proof reading stage. Published in PR
Inflation without inflatons
(abridged)We present a model which predicts inflation without the presence of
inflaton fields, based on the \epsilon R^2 and Starobinsky models. It links the
above models to the observable universe, in particular, to the ratio r of
tensor to scalar fluctuations. In our model, we assume the existence of
particles with the mass M that have a long decay time. These particles which
were gravitationally produced \sim 60e-folds before the end of inflation
produced the nearly scale invariant scalar density fluctuations which are
observed. Gravitational waves (tensor fluctuations) were also produced at this
epoch. The ratio of tensor to scalar fluctuations r (which are to be measured
in the near future to good accuracy) determines M, which together with H_0,
determine the time at the end of inflation, t_end. At t_end, the Hubble
parameter begins to oscillate rapidly, gravitationally producing the bulk of
the M particles, which we identify with the matter content of the universe
today. The time required for the universe to dissipate its vacuum energy into M
particles is found to be t_dis \simeq 6M_Pl^2/M^3. We assume that the time
t_RH, (called the reheating time) needed for the M particles to decay into
relativistic particles, is very much greater than that necessary to create the
M particles, t_dis. From the ratio f\equiv t_dis/t_RH and g_\ast (the total
number of degrees of freedom of the relativistic particles) we can, then,
evaluate the maximum temperature of the universe, T_max, and the reheat
temperature, T_RH, at t_RH. Our model, thus, predicts M, t_dis, t_end, T_max,
T_RH, t_max, and t_RH as a function of r, f, and g_\ast (and to a weaker extent
the particle content of the vacuum near the Planck epoch).Comment: 11 pages, 2 figures. Revised version, accepted for publication in
Phys. Rev.
Graviton Production in Elliptical and Hyperbolic Universes
The problem of cosmological graviton creation for homogeneous and isotropic
universes with elliptical (\vae =+1) and hyperbolical (\vae =-1) geometries
is addressed. The gravitational wave equation is established for a
self-gravitating fluid satisfying the barotropic equation of state , which is the source of the Einstein's equations plus a cosmological
-term. The time dependent part of this equation is exactly solved in
terms of hypergeometric functions for any value of and spatial
curvature \vae. An expression representing an adiabatic vacuum state is then
obtained in terms of associated Legendre functions whenever , where n is an integer. This includes most
cases of physical interest such as . The mechanism of
graviton creation is reviewed and the Bogoliubov coefficients related to
transitions between arbitrary cosmic eras are also explicitly evaluated.Comment: 25 pages, uses REVTE
The Coherent State Representation of Quantum Fluctuations in the Early Universe
Using the squeezed state formalism the coherent state representation of
quantum fluctuations in an expanding universe is derived. It is shown that this
provides a useful alternative to the Wigner function as a phase space
representation of quantum fluctuations. The quantum to classical transition of
fluctuations is naturally implemented by decohering the density matrix in this
representation. The entropy of the decohered vacua is derived. It is shown that
the decoherence process breaks the physical equivalence between vacua that
differ by a coordinate dependent phase generated by a surface term in the
Lagrangian. In particular, scale invariant power spectra are only obtained for
a special choice of surface term.Comment: 25 pages in revtex 3. This version is completely revised with
corrections and significant new calculation
Finite-Range Gravity and Its Role in Gravitational Waves, Black Holes and Cosmology
Theoretical considerations of fundamental physics, as well as certain
cosmological observations, persistently point out to permissibility, and maybe
necessity, of macroscopic modifications of the Einstein general relativity. The
field-theoretical formulation of general relativity helped us to identify the
phenomenological seeds of such modifications. They take place in the form of
very specific mass-terms, which appear in addition to the field-theoretical
analog of the usual Hilbert-Einstein Lagrangian. We interpret the added terms
as masses of the spin-2 and spin-0 gravitons. The arising finite-range gravity
is a fully consistent theory, which smoothly approaches general relativity in
the massless limit, that is, when both masses tend to zero and the range of
gravity tends to infinity. We show that all local weak-field predictions of the
theory are in perfect agreement with the available experimental data. However,
some other conclusions of the non-linear massive theory are in a striking
contrast with those of general relativity. We show in detail how the
arbitrarily small mass-terms eliminate the black hole event horizon and replace
a permanent power-law expansion of a homogeneous isotropic universe with an
oscillatory behaviour. One variant of the theory allows the cosmological scale
factor to exhibit an `accelerated expansion'instead of slowing down to a
regular maximum of expansion. We show in detail why the traditional,
Fierz-Pauli, massive gravity is in conflict not only with the static-field
experiments but also with the available indirect gravitational-wave
observations. At the same time, we demonstrate the incorrectness of the widely
held belief that the non-Fierz-Pauli theories possess `negative energies' and
`instabilities'.Comment: 56 pages including 11 figures; significant modifications; in
particular, we demonstrate the incorrectness of the widely held belief that
the non-Fierz-Pauli theories should suffer from negative energies and
instabilities; to appear in Int. J. Mod. Phys.
Propagation of Light in the Field of Stationary and Radiative Gravitational Multipoles
Extremely high precision of near-future radio/optical interferometric
observatories like SKA, Gaia, SIM and the unparalleled sensitivity of LIGO/LISA
gravitational-wave detectors demands more deep theoretical treatment of
relativistic effects in the propagation of electromagnetic signals through
variable gravitational fields of the solar system, oscillating and precessing
neutron stars, coalescing binary systems, exploding supernova, and colliding
galaxies. Especially important for future gravitational-wave observatories is
the problem of propagation of light rays in the field of multipolar
gravitational waves emitted by a localized source of gravitational radiation.
Present paper suggests physically-adequate and consistent mathematical solution
of this problem in the first post-Minkowskian approximation of General
Relativity which accounts for all time-dependent multipole moments of an
isolated astronomical system.Comment: 36 pages, no figure
Very high frequency gravitational wave background in the universe
Astrophysical sources of high frequency gravitational radiation are
considered in association with a new interest to very sensitive HFGW receivers
required for the laboratory GW Hertz experiment. A special attention is paid to
the phenomenon of primordial black holes evaporation. They act like black body
to all kinds of radiation, including gravitons, and, therefore, emit an
equilibrium spectrum of gravitons during its evaporation. Limit on the density
of high frequency gravitons in the Universe is obtained, and possibilities of
their detection are briefly discussed.Comment: 14 page
Short Wavelength Analysis of the Evolution of Perturbations in a Two-component Cosmological Fluid
The equations describing a two-component cosmological fluid with linearized
density perturbations are investigated in the small wavelength or large
limit. The equations are formulated to include a baryonic component, as well as
either a hot dark matter (HDM) or cold dark matter (CDM) component. Previous
work done on such a system in static spacetime is extended to reveal some
interesting physical properties, such as the Jeans wavenumber of the mixture,
and resonant mode amplitudes. A WKB technique is then developed to study the
expanding universe equations in detail, and to see whether such physical
properties are also of relevance in this more realistic scenario. The Jeans
wavenumber of the mixture is re-interpreted for the case of an expanding
background spacetime. The various modes are obtained to leading order, and the
amplitudes of the modes are examined in detail to compare to the resonances
observed in the static spacetime results. It is found that some conclusions
made in the literature about static spacetime results cannot be carried over to
an expanding cosmology.Comment: 42 pages, 12 figure
Sensitivity of wide band detectors to quintessential gravitons
There are no reasons why the energy spectra of the relic gravitons, amplified
by the pumping action of the background geometry, should not increase at high
frequencies. A typical example of this behavior are quintessential inflationary
models where the slopes of the energy spectra can be either blue or mildly
violet. In comparing the predictions of scenarios leading to blue and violet
graviton spectra we face the problem of correctly deriving the sensitivities of
the interferometric detectors. Indeed, the expression of the signal-to-noise
ratio not only depends upon the noise power spectra of the detectors but also
upon the spectral form of the signal and, therefore, one can reasonably expect
that models with different spectral behaviors will produce different
signal-to-noise ratios. By assuming monotonic (blue) spectra of relic gravitons
we will give general expressions for the signal-to-noise ratio in this class of
models. As an example we studied the case of quintessential gravitons. The
minimum achievable sensitivity to of different pairs of
detectors is computed, and compared with the theoretical expectations.Comment: 10 pages in Revtex style, 3 figure
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