Axi-Higgs Cosmology

by Dr Lingfeng Li (Hong Kong University of Science and Technology)

Thursday 22 Jul 2021, 16:00 → 17:30 Asia/Seoul

Title: Axi-Higgs Cosmology

Speaker: Lingfeng Li (Hong Kong University of Science and Technology)

Abstract: If the electroweak Higgs vacuum expectation value $v$ in early universe is $\sim 1\mathrm{\%}$ higher than its present value $v_0=246\mathrm{G}\mathrm{e}\mathrm{V}$, the ${}^7$Li puzzle in BBN and the CMB/$\mathrm{\Lambda }$CDM tension with late-universe measurements on Hubble parameter are mitigated.  We propose a model of an axion coupled to the Higgs field, named “axi-Higgs”, with its mass $m_a\sim {10}^{-30}$–${10}^{-29}\mathrm{e}\mathrm{V}$ and decay constant $f_a\sim {10}^{17}$–${10}^{18}\mathrm{G}\mathrm{e}\mathrm{V}$, to achieve this goal.  The axion initial value $a_{\mathrm{i}\mathrm{n}\mathrm{i}}$ yields an initial $\mathrm{\Delta }{v}_{\mathrm{i}\mathrm{n}\mathrm{i}}/v_0\sim 0.01$ throughout the BBN-recombination epoch and a percent level contribution to the total matter density today.  Because of its very large de Broglie wavelength, this axion matter density ${\omega }_a$ suppresses the matter power spectrum, alleviating the CMB/$\mathrm{\Lambda }$CDM $S_8/{\sigma }_8$ tension with the weak-lensing data.  It also explains the recently reported isotropic cosmic birefringence by its coupling with photons.  Adding the axion ($m\sim {10}^{-22}\mathrm{e}\mathrm{V}$) in the fuzzy dark matter model to the axi-Higgs model allows bigger $\mathrm{\Delta }{v}_{\mathrm{r}\mathrm{e}\mathrm{c}}$ and ${\omega }_a$ to address the Hubble and $S_8/{\sigma }_8$ tensions simultaneously.  The model predicts that $\mathrm{\Delta }v$ may be detected by the spectral measurements of quasars, while its oscillation may be observed in the atomic clock measurements.

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