2018/11/08 by Chi-Ting Chiang, Anže Slosar, Chiang, Chi-Ting +1
Physics and Astronomy · #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #astro-ph.CO
paper · pdf · doi:10.48550/arxiv.1811.03624
4 pages, 4 figures, 1 table
arxiv created 2018/11/08 · arxiv updated 2018/11/12
Measurements of the Hubble parameter from the distance ladder are in tension with indirect measurements based on the cosmic microwave background (CMB) data and the inverse distance ladder measurements at 3-4 σ level. We consider phenomenological modification to the timing and width of the recombination process and show that they can significantly affect this tension. This possibility is appealing, because such modification affects both the distance to the last scattering surface and the calibration of the baryon acoustic oscillations (BAO) ruler. Moreover, because only a very small fraction of the most energetic photons keep the early universe in the plasma state, it is possible that such modification could occur without affecting the energy density budget of the universe or being incompatible with the very tight limits on the departure from the black-body spectrum of CMB. In particular, we find that under this simplified model, with a conservative subset of Planck data alone, H0=73.44-6.77+5.50~\rm km s-1 \rm Mpc-1 and in combination with BAO data H0=68.86-1.35+1.31~\rm km s-1 \rm Mpc-1, decreasing the tension to ∼ 2σ level. However, when combined with Planck lensing reconstruction and high-ℓ polarization data, the tension climbs back to ∼ 2.7σ, despite the uncertainty on non-ladder H0 measurement more than doubling.