Cosmic Equation of state from Strong Gravitational Lensing Systems

Abstract

Here we present the joint analysis of five dark energy models using the data from Type Ia Supernovae (data from recent Union2 compilation), Cosmic Microwave Background (CMB) shift parameter R (WMAP7 data), Baryon Acoustic Oscillation (BAO) and strongly gravitationally lensed quasar-galaxy systems (combined data sets from SLACS and LSD surveys). These different tests falls into two distinct classes. The first one makes use of the angular diameter distance, and refers to the so called standard rulers. The second uses the luminosity distance and then we deal with standard candles. The two distance concepts, although theoretically related to each other, in practice have different systematic uncertainties and different parameter degeneracies. Hence their joint analysis is more restrictive in the parameter space. We have considered ΛCDM model, two Quintessence scenarios (with constant and variable equation of state), generalized Chaplygin gas and braneworld (Dvali, Gabadagdze, Porrati -DGP) model. The best fits we obtained for the model parameters in joint analysis turned out to prefer cases effectively equivalent to ΛCDM model. Our findings are in agreement with parallel studies performed by other authors on different sets of diagnostic probes. We also tried to answer question: "Which model is the best?" with the aid of two informationtheoretic criteria: the Akaike Criterion (AIC) and Bayesian Information Criterion(BIC). It lead us to similar conclusion that the concordance model ΛCDM is clearly preferred in joint analysis. The quintessence (both having constant or time varying equation of state), and Chaplygin gas get considerably less support from the data while the brane world (DGP) scenario is practically ruled out.