Seminar detail: Implications of Hubble tensions for very early universe cosmology

Date&Time	Tue May 10 2022 (17:00 - 18:00)
Speaker	Wen Yin
Affiliation	Tohoku University
Title	Implications of Hubble tensions for very early universe cosmology
Abstract	Recently, a low-z measurement of the Hubble constant was reported by the SH0ES Team. The long-standing Hubble tension, i.e. the difference between the Hubble constant from the local measurements and that inferred from the cosmic microwave background data based on the $\Lambda$CDM model, was further strengthened. There are many cosmological models modifying the cosmology after and around the recombination era to alleviate this tension. Some of the models alter the small-scale fluctuation amplitude relative to larger scales and thus require a significant modification of the primordial density perturbation, especially the scalar spectral index, $n_s$. In certain promising models, $n_s$ is favored to be larger than the $\Lambda$CDM prediction, and even the scale-invariant one, $n_s=1$, is allowed. In this talk, I focus on the very early Universe models to study the implication of such unusual $n_s$. In particular, we find that an axiverse with axions in the equilibrium distribution during inflation can be easily consistent with $n_s = 1$. This is because the axion behaves as a curvaton with a mass much smaller than the inflationary Hubble parameter. I also discuss other explanations of $n_s$ different from that obtained based on the $\Lambda$CDM.
Remarks
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