Hints of FLRW breakdown from supernovae
Chethan Krishnan, Roya Mohayaee, Eoin Ó Colgáin, M. M. Sheikh-Jabbari, Lu Yin
Abstract
A 10% difference in the scale for the Hubble parameter constitutes a clear problem for cosmology. Here, considering angular distribution of type Ia supernovae (SN) within the Pantheon compilation and working within flat $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ cosmology, we observe a correlation between higher ${H}_{0}$ and the CMB dipole direction, confirming our previous results for strongly lensed quasars [Classical Quantum Gravity 38, 184001 (2021)]. Concretely, we record a $\ensuremath{\sim}1\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ variation in ${H}_{0}$ at antipodal points on the sky within the Pantheon sample, which is evident in the Low $z$ subsample ($z\ensuremath{\lesssim}0.075$) and gets enhanced by higher redshift SN. Our work raises the possibility that we may be at the precision required to probe anisotropic Hubble expansions, while providing a concrete prediction for future inferences of ${H}_{0}$.