Cosmic transparency and acceleration

Abstract

In this paper, by considering an absorption probability independent of photon wavelength, we show that current type Ia supernovae (SNe Ia) and gamma-ray burst (GRB) observations plus high-redshift measurements of the cosmic microwave background (CMB) radiation temperature support cosmic acceleration regardless of the transparent-universe assumption. Two flat scenarios are considered in our analyses: the Lambda CDM model and a kinematic model. We consider tau(z) = 2 ln(1 + z)(epsilon), where tau(z) the opacity between an observer at z = 0 and a source at z. This choice is equivalent to deforming the cosmic distance duality relation as DLDA-1 = (1 + z)(2+epsilon) and, if the absorption probability is independent of photon wavelength, the CMB temperature evolution law is T-CMB (z) = T-0(1 + z)(1+2 epsilon/3). By marginalizing on the epsilon parameter, our analyses rule out a decelerating universe at 99.99% C.L. for all scenarios considered. Interestingly, by considering only SNe Ia and GRBs observations, we obtain that a decelerated universe-indicated by O-Lambda <= 0.33 and q(0) > 0-is ruled out around 1.5 sigma C.L. and 2 sigma C.L., respectively, regardless of the transparent-universe assumption.