http://arxiv.org/abs/1808.04597
Recent observations reveal a bulk flow in the local Universe which is faster and extends to larger scales than is expected around a typical observer in the standard $\Lambda$CDM cosmology. The deceleration parameter $q_0$ derived from local observations is then expected to show a scale-dependent dipolar modulation. From a maximum likelihood analysis of the Joint Lightcurve Analysis (JLA) catalogue of Type Ia supernovae we do find such a dipole in $q_0$ extending out to $z \sim 0.2$, with a magnitude comparable to its monopole. Although not statistically significant in current data, such a dipole must be allowed for, especially in analysing surveys with incomplete sky coverage such as JLA and its successor Pantheon; out of 740 (1048) SNe IA in the JLA (Pantheon) catalogue, 632 (890) are in the hemisphere opposite to the direction of bulk flow for which their redshifts have been corrected. However when we do so, the monopole component of $q_0$, which has been widely ascribed to a cosmological constant (dark energy), drops in statistical significance and becomes consistent with zero at $2\sigma$ (95\% c.l.). This suggests that the apparent acceleration of the expansion rate deduced from supernovae may be an artefact of our bulk flow.
J. Colin, R. Mohayaee, M. Rameez, et. al.
Wed, 15 Aug 18
6/69
Comments: 7 pages, 3 figures, 2 tables
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