Testing the isotropy of the Universe with type Ia supernovae in a model-independent way

Abstract

In this paper, we study an anisotropic universe model with Bianchi-I metric using Joint Light-curve Analysis (JLA) sample of type Ia supernovae (SNe Ia). Because light-curve parameters of SNe Ia vary with different cosmological models and SNe Ia samples, we fit the SNe Ia light-curve parameters and cosmological parameters simultaneously employing Markov Chain Monte Carlo method. Therefore, the results on the amount of deviation from isotropy of the dark energy equation of state ($\hat{I}´$), and the level of anisotropy of the large-scale geometry ($\hat{I}{\pounds }_0$) at present, are totally model-independent. The constraints on the skewness and cosmic shear are $-0.101<\hat{I}´<0.071$ and $-0.007<\hat{I}{\pounds }_0<0.008$. This result is consistent with a standard isotropic universe ($\hat{I}´=\hat{I}{\pounds }_0=0$). However, a moderate level of anisotropy in the geometry of the Universe and the equation of state of dark energy, is allowed. Besides, there is no obvious evidence for a preferred direction of anisotropic axis in this model.

10 pages, 5 figures, 5 tables, accepted for publication in MNRAS