Tests of the cosmic distance duality relation

We discuss model- independent tests of the so-called cosmic distance duality relation (CDDR), eta = D-L(L)(1+ z)(-2)/D-A(z) = 1, where D-A(z) and D-L(z) are the angular diameter and luminosity distances, respectively. Using the general expression for X-ray gas mass fraction (f(gas)) of galaxy clusters, f(gas)infinity 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 f(X-ray) and Sunyaev-Zeldovich gas mass fraction (f(SZE)) observations is given by integral(SZE) =eta integral(X-ray), where. quantifies deviations from the CDDR. In order to perform our analysis we use 38 f(gas) measurements recently studied by two different groups.