How Axi-Higgs Model Resolves the Hubble Constant and S8 Tensions Simultaneously? (Astronomy)

Fung and colleagues in their recent paper demonstrated that, Axi-higgs model resolves the H0 and S8 tensions simultaneously, by correlating the axion impacts on the early and late universe.

The ΛCDM model provides an excellent fit to the Cosmic Microwave Background (CMB) data. However, as data improves, a significant discrepancy emerges, when its determination of the Hubble constant H0 is compared to local distance-redshift (DR) measurements. The recently proposed, axi-Higgs model suggests a potential solution to the H0 tension by coupling ultralight axions to the Higgs field. This model can further explain the 7Li puzzle in Big-Bang nucleosynthesis (BBN), as well as the clustering S8 tension with the weak-lensing (WL) data and the observed isotropic cosmic birefringence (ICB) in CMB. Now, Leo Fung and colleagues demonstrated how this model resolves the H0 and S8 tensions simultaneously, by correlating the time-varying state of an ultralight axion with early and late universe. Their study recently appeared in Arxiv.

They found that:

  • In the early universe (z > z1), this axion field behaves like dark energy (DE). Its main impact is to drive a positive shift of the Higgs Vaccum Expectation Value (VEV). Such a shift will reduce the cross section of Thomson scattering (∝ me¯2) and modify various atomic processes crucial to electron recombination and photoionization, and therefore, e.g., increase recombination redshift (z∗) and decrease the comoving sound horizon and damping scale at z∗.
  • In the late universe (z < z1), this axion field behaves like dark matter (DM). Its main impacts are to: (1) increase the hubble flow, (H(z)) value during this epoch by providing additional contribution to the energy density and hence, e.g., reduce the comoving diameter distance at z∗ and zeff; (2) suppress the formation of the structure at a galactic clustering scale and even above, with its super-long de Broglie wavelength; (3) shift the v (or me) value in the early universe to its today’s value v0; (4) generate the observed ICB.

“This correlation, together with the multiple roles played by the axion a1, distinguish this model from the class of popular proposals to address the H0 tension, namely increasing the H(z) values in the early universe with additional components, such as early DE and self-interacting neutrinos.”

Finally, by combining the CMB+BAO+WL+SN data with the local distance-redshift (DR) measurements they found H0 = 72.31 ± 0.7 km/s/Mpc, while S8 is 0.762 ± 0.010. (for more paramater values refer table 1 given below).

TABLE I. Marginalized parameter values in the ΛCDM model and the axi-Higgs model. © Fung et al.

“We emphasize that a full test of this model is at hand, due to the oncoming atomic-clock and the quasar spectral measurements with the data expected to be collected by, e.g., Thirty Meter Telescope and James Webb Space Telescope.”

— concluded authors of the study

Featured image: Posterior distributions of the model parameters in the axi-Higgs benchmark. The shaded olive and grey bands represent the local DR measurement of H0 = 73.2±1.3 km/s/Mpc from the latest SH0ES2020 and the weak-lensing measurement of S8 = 0.766 ± 0.014 from KiDS-1000, respectively © Fung et al.

Reference: Leo WH Fung, Lingfeng Li, Tao Liu, Hoang Nhan Luu, Yu-Cheng Qiu, S.-H. Henry Tye, “The Hubble Constant in the Axi-Higgs Universe”, pp. 1-10, 2021.

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