PROBING THE ISOTROPY OF COSMIC ACCELERATION TRACED BY TYPE Ia SUPERNOVAE

Abstract

We present a method to test the isotropy of the magnitude-redshift relation of Type Ia Supernovae (SNe Ia) and single out the most discrepant direction (in terms of the signal-to-noise ratio) with respect to the all-sky data. Our technique accounts for possible directional variations of the corrections for SNe Ia and yields all-sky maps of the best-fit cosmological parameters with arbitrary angular resolution. To show its potential, we apply our method to the recent Union2.1 compilation, building maps with three different angular resolutions. We use a Monte Carlo method to estimate the statistical significance with which we could reject the null hypothesis that the magnitude-redshift relation is isotropic based on the properties of the observed most discrepant directions. We find that, based on pure signal-tonoise arguments, the null hypothesis cannot be rejected at any meaningful confidence level. However, if we also consider that the strongest deviations in the Union2.1 sample closely align with the dipole temperature anisotropy of the cosmic microwave background, we find that the null hypothesis should be rejected at the 95 − 99 per cent confidence level, slightly depending on the angular resolution of the study. If this result is not due to a statistical fluke, it might either indicate that the SN data have not been cleaned from all possible systematics or even point towards new physics. We finally discuss future perspectives in the field for achieving larger and more uniform data sets that will vastly improve the quality of the results and optimally exploit our method.

Geodesic-light-cone coordinates and the Bianchi I spacetime

“…In ref. [45], the Jacobi matrix in a conformal Bianchi I spacetime is found to be 33) where the integral matrix I ij is defined by…”

Anisotropy of the Universe via the Pantheon supernovae sample revisited

“…As standard candles, the supernovae of type Ia (SNe Ia) have been used to investigate the accelerating expansion of the Universe (Riess et al 1998;Perlmutter et al 1999), and the possible deviations from the isotropic universe ( Heneka et al 2014;Bengaly et al 2015;Li et al 2015;Javanmardi et al 2015;Lin et al 2016a,b;Salehi & Aftabi 2016;Salehi & Setare 2017;Li & Lin 2017;Ghodsi et al 2017;Wang & Wang 2018;Andrade et al 2018b;Chang et al 2018a;Deng & Wei 2018b), with the datasets given by the Union2 sample (Amanullah et al 2010), the Union2.1 sample (Suzuki et al 2012) and the "Joint Lightcurve Analysis" (JLA) sample (Betoule et al 2014). Antoniou & Perivolaropoulos (2010) first used the hemisphere comparison (HC) method to the Union2 sample and they found a certain cosmological preferred direction with maximum accelerating expansion rate.…”

Angular distribution of cosmological parameters as a probe of space-time inhomogeneities

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