Tests of the cosmic distance duality relation

We discuss model-independent tests of the so-called cosmic distance duality relation (CDDR),η = DL(L)(1+z)−2/DA(z) = 1, where DA(z) and DL(z) are the angular diameter and luminosity distances, respectively. Using the general expression for X-ray gas mass fraction (fgas) of galaxy clusters, fgas∝DLDA1/2, we show that fgas observations jointly with type Ia supernovae (SNe Ia) data furnish a validity test for the CDDR. We also show that the relation between current fX-ray and Sunyaev-Zeldovich gas mass fraction (fSZE) observations is given by fSZE = ηfX-ray, where η quantifies deviations from the CDDR. In order to perform our analysis we use 38 fgas measurements recently studied by two different groups.