Testing the isotropy of the Universe by using the JLA compilation of type-Ia supernovae

Abstract

We probe the possible anisotropy of the Universe by using the JLA compilation of type-Ia supernovae. We apply the Markov Chain Monte Carlo (MCMC) method to constrain the amplitude and direction of anisotropy in three cosmological models. For the dipole-modulated $\Lambda$CDM model, the anisotropic amplitude is consistent with zero at $68\%$ C.L., and has an upper bound $A_D<1.98\times10^{-3}$ at $95\%$ C.L. Regardless of much larger uncertainty, we find the dipole direction of JLA is amazingly opposite to that of Union2. Similar results are found for the dipole-modulated $w$CDM and CPL models. Thus, the Universe is still well consistent with the isotropy according to the JLA compilation.