Inferences of $H_0$ in presence of a non-standard recombination

• DOI: 10.48550/arxiv.1811.03624
• Publication Date: 2018-01-01
• Authors: Chi-Ting Chiang; Anže Slosar
• Keywords: Sigma

Measurements of the Hubble parameter from distance ladder are in tension with indirect measurements based on cosmic microwave background (CMB) data and inverse at 3-4 $\sigma$ level. We consider phenomenological modification to timing width recombination process show that they can significantly affect this tension. This possibility is appealing, because such affects both last scattering surface calibration baryon acoustic oscillations (BAO) ruler. Moreover, only a very small fraction most energetic photons keep early universe plasma state, it possible could occur without affecting energy density budget or being incompatible tight limits departure black-body spectrum CMB. In particular, we find under simplified model, conservative subset Planck alone, $H_0=73.44_{-6.77}^{+5.50}~{\rm km\ s}^{-1}\ {\rm Mpc}^{-1}$ combination BAO $H_0=68.86_{-1.35}^{+1.31}~{\rm Mpc}^{-1}$, decreasing $\sim 2\sigma$ However, when combined lensing reconstruction high-$\ell$ polarization data, climbs back 2.7\sigma$, despite uncertainty non-ladder $H_0$ measurement more than doubling.