138 research outputs found
Generalized Chaplygin Gas Models tested with SNIa
The so called Generalized Chaplygin Gas (GCG) with the equation of state was recently proposed as a candidate for dark
energy in the Universe. In this paper we confront the GCG with SNIa data.
Specifically we have tested the GCG cosmology in three different classes of
models with (1) , ; (2) ,
and (3) , , as well as the
model withouth any assumption on . The best fitted models are
obtained by minimalizing the function and levels in the
plane. We supplemented our analysis with confidence intervals
in the plane, as well as one-dimensional probability
distribution functions for models parameter. The general conclusion is that
SNIa data strongly support the Chaplygin gas (with ). Extending our
analysisby relaxing the flat prior lead to the result that even though the best
fitted values of are formally non-zero, still they are close to flat
case. It should be viewed as an advantage of the GCG model since in similar
analysisof CDM model high negative value of were found to
be bestfitted to the data and independent inspiration from CMBR and
extragalactic astronomy has been invoked to fix the curvature problem. Our
results show clearly that in Generalized Chaplygin Gas cosmology distant
supernovae should be brighter than in CDM model.This prediction seems
to be confirmed with new Riess high redshift SNIa sample. Moreover, we argue
that with the future SNAP data it would be possible to differentiate between
models with various value of parameter and/or discriminated between
GCG, Cardassian and CDM modelsComment: 54 pages 29 figures improved version analysis flat prior relaxed high
redshift Riess SNIa sample include
Perspective for testing dark energy scenarios with advanced LIGO type gravity wave experiments
Future generation of interferometric gravitational wave detectors is hoped to provide accurate measurements of the final stages of binary in-spirals. The sources probed by such experiments are of extragalactic origin
and the observed chirp mass distribution carries information about their redshifts. Moreover the luminosity distance is directly observable is such experiments. This creates the possibility to establish a new kind of cosmo-
logical tests, supplementary to more standard ones. The paper discusses the utility of gravity wave experiments for testing the dark energy in the Universe, which is one of the most important issues in modern cosmology
Quintessence in advanced gravity wave experiments
Recent observations of distant type la supernovae light-curves suggest
that the expansion of the Universe has recently begun to accelerate.
A popular explanation of present accelerating expansion of the Universe
is to assume that some part Qq of the matter-energy density is
in the form of dark component called “the quintessence” with the equation
of state pq = w()q with w > — 1. Determining the cosmic equation
of state is, therefore, one of the greatest challenges of modern cosmology.
Future generation of interferometrie gravitational wave detectors is
hoped to detect the final stages of binary inspirals. The sources probed by
such experiments are of extragalactic origin and the observed chirp mass
can be translated into the redshift of the source. Moreover, the luminosity
distance is a direct observable in such experiments. This creates the
possibility to establish a new kind of cosmological tests, supplementary to
more standard ones. In this paper we review the standard methods of probing
the dark energy, introduce the basic concepts underlying the utility of
advanced LIGO type interferometrie experiments in making cosmological
inferences and we extend some recent results in this respect to the case of
z varying equation of state[…
The wave nature of continuous gravitational waves from microlensing
Gravitational wave predicted by General Relativity is the transverse wave of
spatial strain. Several gravitational waveform signals from binary black holes
and from a binary neutron star system accompanied by electromagnetic
counterparts have been recorded by advanced LIGO and advanced Virgo. In analogy
to light, the spatial fringes of diffraction and interference should also exist
as the important features of gravitational waves. We propose that observational
detection of such fringes could be achieved through gravitational lensing of
continuous gravitational waves. The lenses would play the role of the
diffraction barriers. Considering peculiar motions of the observer, the lens
and the source, the spatial amplitude variation of diffraction or interference
fringes should be detectable as an amplitude modulation of monochromatic
gravitational signal.Comment: Accepted for publication in The Astrophysical Journa
White dwarfs as a source of constraints on exotic physics
In this paper we briefly review main ideas underlying the constraints
on exotic physics coming from Astrophysics already used by the others.
Next we present a new bound coming from the White Dwarf cooling. Such
stringent bound is possible due to accurate measurements offered by astroseismology.
Specifically we consider the G117-B15A pulsating white dwarf
(ZZ Ceti star) for which the speed of the period increase has been accurately
measured for its fundamental oscillation mode. It has been claimed
that this mode detected in G117-B15A is perhaps the most stable oscillation
ever recorded in the optical band. Then we review our result concerning the
bounds on compactification scale in the theory with large extra dimensions
according to Arkani-Hamed, Dimopoulos and Dvali. Because an additional
channel of energy loss (Kaluza-Klein gravitons) would speed up the cooling
rate, one is able to use the aforementioned stability to derive a bound on
compactification scale. We find the lower bound on compactification scale
to be Ms > 14.3 TeV/c2 which is more stringent than solar or red-giant
bounds, as well as the bound coming from LEP. In final section we point out
that pulsating hot “pre-White Dwarf” PG 1159-035 (GW Virginis) whose
oscillation period increases at the rate of the order of magnitude larger than
predicted could be a promising object for further investigations
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