Evidence for anisotropy of cosmic acceleration

Jacques Colin; Roya Mohayaee; Mohamed Rameez; Subir Sarkar

doi:10.1051/0004-6361/201936373

paper

Evidence for anisotropy of cosmic acceleration

arXiv:1808.04597 · doi:10.1051/0004-6361/201936373

Abstract

Observations reveal a `bulk flow' in the local Universe which is faster and extends to much larger scales than is expected around a typical observer in the standard $Λ$ CDM cosmology. This is expected to result in a scale-dependent dipolar modulation of the acceleration of the expansion rate inferred from observations of objects within the bulk flow. From a maximum-likelihood analysis of the Joint Lightcurve Analysis (JLA) catalogue of Type Ia supernovae we find that the deceleration parameter, in addition to a small monopole, indeed has a much bigger dipole component aligned with the CMB dipole which falls exponentially with redshift $z$ : $q_{0} = q_{m} + q_{d} . n^exp (- z / S)$ . The best fit to data yields $q_{d} = - 8.03$ and $S = 0.0262 (\Rightarrow d \sim 100 Mpc)$ , rejecting isotropy ( $q_{d} = 0$ ) with $3.9 σ$ statistical significance, while $q_{m} = - 0.157$ and consistent with no acceleration ( $q_{m} = 0$ ) at $1.4 σ$ . Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of `dark energy' in the Universe.

arXiv comment7 pages, 4 figures, 4 tables; Title changed, Bayesian information criterion values added, conclusions strengthened; Results can be reproduced using code at: https://github.com/rameez3333/Dipole_JLA ; Accepted for publication in Astronomy & Astrophysics Letters

Evidence for anisotropy of cosmic acceleration

Abstract

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