Anisotropy of Cosmic Acceleration

TL;DR

This study investigates the anisotropy of cosmic acceleration using supernova data, revealing a significant dipole pattern in the deceleration parameter that is nearly perpendicular to the CMB dipole, suggesting potential anisotropic features in cosmic expansion.

Contribution

The paper introduces a novel analysis of cosmic acceleration anisotropy by mapping the deceleration parameter across different sky regions using supernova data, highlighting a significant dipole component.

Findings

Detected a dipole anisotropy in cosmic acceleration with >2-sigma significance.

Found the dipole direction nearly perpendicular to the CMB kinematic dipole.

Identified the anisotropy pattern as potentially anomalous at the 1-in-10 level.

Abstract

In this paper, we study the anisotropy of cosmic acceleration by dividing the Union2 Type Ia supernova dataset into 12 subsets according to their positions in Galactic coordinate system. In each region, we derive the deceleration parameter $q_0$ as the diagnostic to quantify the anisotropy level in the corresponding direction, and construct $q_0$ anisotropic maps by combining these $q_0$ values. In addition to the monopole component, we find the significant dipole effect in the $q_0$-maps with the amplitude $A_1=0.466^{+0.255}_{-0.205}$, which deviates from zero at more than 2-$\sigma$ level. The direction of the best-fit dipole is ($\theta=108.8^{\circ}$, $\phi=187.0^{\circ}$) in Galactic system. Interesting enough, we find the direction of this dipole is nearly perpendicular to the CMB kinematic dipole, and the angle between them is $95.7^{\circ}$. The perpendicular relation is anomalous at the 1-in-10 level.