On the Hubble expansion in a Big Bang quantum cosmology

The Hubble expansion of the Universe is considered in the classical limit of a Big Bang quantum cosmology. In an IR-consistent coupling to the the bare cosmological constant, we infer a dark energy as a relic of the Big Bang by loss of time-translation invariance on a Hubble time-scale. This dark energy is identified with the trace $J$ of the Schouten tensor permitting an analytic solution $H(z)$. Anchored by the {\em Baryonic Accoustic Oscillations}, $J$CDM predicts a Hubble constant $H_0=\sqrt{6\mathrm{/}5}{H}_0^{\mathrm{\Lambda }}$ alleviating $H_0$-tension between the Local Distance Ladder and $H_0^{\mathrm{\Lambda }}$ in $\mathrm{\Lambda }$CDM, whose dark energy $\mathrm{\Lambda }$ is a constant. Emulated by $w(a)\mathrm{\Lambda }$CDM, a CAMB analysis shows a $J$CDM fit to the {\em Planck} 2018 $C_l^{TT}$ power spectrum on par with $\mathrm{\Lambda }$CDM with small positive curvature consistent with {\em Planck}-$\mathrm{\Lambda }$CDM with no extra relativistic degrees of freedom. In late-time cosmology, $J$CDM is also consistent with the BAO recently measured by DESI. { $J$CDM offers a novel framework to address $H_0$-tension, predicting background quantities consistent with the uncertainties in BAO measurements and early-Universe observations.} It predicts a deceleration parameter $q_0\simeq -1$, that may be tested with upcoming low-redshift galaxy surveys.