Reconciling Hubble Constant Discrepancy from Holographic Dark Energy.

Holographic dark energy (HDE) models the vacuum energy in a cosmic IR region whose total energy saturates the limit of collapsing into a black hole. HDE predicts that the dark energy equation of the state (EoS) transiting from greater than $-1$ regime to less than $-1$, accelerating the Universe slower at early stage and faster at late stage. We show that this model provides a natural reconciliation of the Hubble constant ($H_{0}$) discrepancy between CMB measurement and local measurements. With Planck+BAO data, we fit HDE model's $H_0$ as $71.54\pm1.78\,\mathrm{km\,s^{-1} Mpc^{-1}}$, consistent with local $H_{0}$ measurements by LMC Cepheid Standards (Riess et al. 2019) at $1.4\sigma$ level. Combining Planck+BAO+R19, we find $c=0.51\pm0.02$ and $H_0^{}\! = 73.12\pm 1.14\,\mathrm{km \,s^{-1} Mpc^{-1}}$, which fits cosmological data at all redshifts. Future CMB and large-scale structure surveys will further probe this scenario.