A Decisive test to confirm or rule out the existence of dark matter emulators using gravitational wave observations

We consider stable modified theories of gravity that reproduce galactic rotation curves and the observed amount of weak lensing without dark matter. In any such model gravity waves follow a different geodesic from that of other massless particles. For a specific class of models which we call "dark matter emulators," over cosmological distances this results in an easily detectable and difference between the arrival times of the pulse of gravity waves from some cosmic event and those of photons or neutrinos. For a repeat of SN 1987a (which took place in the Large Magellanic Cloud) the time lag is in the range of days. For the recent gamma ray burst, GRB 070201 (which seems to have taken place on the edge of the Andromeda galaxy) the time lag would be in the range of about two years.Comment: 4 Pages, no figures, Contributed to 12th Annual Gravitational Wave Data Analysis Workshop (GWDAW-12 2007): Connecting Gravitational Waves with Observational Astrophysics, Cambridge, Massachusetts, 13-16 Dec 200

The universe dominated by the extended Chaplygin gas

In this paper, we consider a universe dominated by the extended Chaplygin gas which recently proposed as the last version of Chaplygin gas models. Here, we only consider the second order term which recovers quadratic barotropic fluid equation of state. The density perturbations analyzed in both relativistic and Newtonian regimes and show that the model is stable without any phase transition and critical point. We confirmed stability of the model using thermodynamics point of view.Comment: 17 pages. Accepted in MPL

FRW cosmology with the extended Chaplygin gas

In this paper, we propose extended Chaplygin gas equation of state for which it recovers barotropic fluid with quadratic equation of state. We use numerical method to investigate the behavior of some cosmological parameters such as scale factor, Hubble expansion parameter, energy density and deceleration parameter. We also discuss about the resulting effective equation of state parameter. Using density perturbations we investigate the stability of the theory.Comment: 20 page

Higher order corrections of the extended Chaplygin gas cosmology with varying GG and Λ\Lambda

In this paper, we study two different models of dark energy based on Chaplygin gas equation of state. The first model is the variable modified Chaplygin gas while the second one is the extended Chaplygin gas. Both models are considered in the framework of higher order $f(R)$ modified gravity. We also consider the case of time varying gravitational constant $G$ and $\Lambda$ for both models. We investigate some cosmological parameters such as the Hubble, the deceleration and the equation of state parameters. Then we showed that the model that we considered, extended Chaplygin gas with time-dependent $G$ and $\Lambda$, is consistent with the observational data. Finally we conclude with the discussion of cosmological perturbations of our model.Comment: Perturbation analysis added, typos corrected, references adde