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Prof. Subir Sarkar

Rudolf Peierls Centre for Theoretical Physics, University of Oxford
Evidence for anisotropy of cosmic acceleration

Recent observations reveal a bulk (non-Hubble) flow in our local Universe which is faster and extends to longer scales than is expected around a typical observer in the standard LCDM cosmology. The deceleration parameter of the Hubble expansion rate inferred from local observations is then expected to show a scale-dependent dipolar modulation. From a maximum-likelihood analysis of the Joint Lightcurve Analysis catalogue of Type Ia supernovae we find that the deceleration parameter, in addition to a small monopole (consistent with no acceleration at 1.4sigma) indeed has a ~50 times bigger dipole component (rejecting isotropy at 3.9sigma) which is aligned with the CMB dipole. Thus the cosmic acceleration deduced from supernovae may just be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of dark energy in the Universe. ( A&A 631 (2019) L13 , arXiv:1912.04257 , arXiv:2003.10420 )

Online Colloquium
May 28, 2020, 16:00 hrs.