Observational cosmology and the cosmic distance-duality relation
  We study the validity of cosmic distance duality relation between angular diameter and luminosity distances. To test this duality relation we use the latest Union2 Supernovae Type Ia (SNe Ia) data for estimating the luminosity distance. The estimation of angular diameter distance comes from the samples of galaxy clusters (real and mock) and FRIIb radio galaxies. We parameterize the distance duality relation as a function of redshift in four different ways and we find that the mock data set, which assumes a spherical isothermal $\beta$ model for the galaxy clusters does not accommodate the distance duality relation while the real data set which assumes elliptical $\beta$ model does. 
S Jhingan, D Jain and R Nair
gr-qc