Generalized Chaplygin Gas Models tested with SNIa

The so called Generalized Chaplygin Gas (GCG) with the equation of state $p = - \frac{A}{{\rho}^{\alpha}}$ 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) $\Omega_m= 0.3$, $\Omega_{Ch}= 0.7$; (2) $\Omega_m= 0.05$, $\Omega_{Ch}= 0.95$ and (3) $\Omega_m = 0$, $\Omega_{Ch} = 1$, as well as the model withouth any assumption on $\Omega_m$. The best fitted models are obtained by minimalizing the $\chi^2$ function and $\chi^2$ levels in the $(A_0, \alpha)$ plane. We supplemented our analysis with confidence intervals in the $(A_0, \alpha)$ 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 $\alpha = 1$). Extending our analysisby relaxing the flat prior lead to the result that even though the best fitted values of $\Omega_k$ 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 $\Lambda$CDM model high negative value of $\Omega_{k}$ 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 $z >1$ supernovae should be brighter than in $\Lambda$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 $\alpha$ parameter and/or discriminated between GCG, Cardassian and $\Lambda$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