On Larger $H_0$ Values in the CMB Dipole Direction

Understand

On the assumption that quasars (QSO) and gamma-ray bursts (GRB) represent \textit{standardisable candles}, we provide evidence that the Hubble constant $H_0$ adopts larger values in hemispheres aligned with the CMB dipole direction.

• If substantiated, this trend signals a departure from FLRW cosmology.
• In particular, QSOs show a definite trend, whereas our findings in GRBs are consistent with an isotropic Universe, but we show in a sample of GRBs calibrated with Type Ia supernovae (SN) that this conclusion may change as one focuses on GRBs more closely (mis)aligned with the CMB dipole direction.
• The statistical significance in QSOs alone is $\gtrsim 2 \sigma$ and when combined with similar trends in strong lensing, Type Ia SN and calibrated GRBs, this increases to $\sim 3 \sigma$.