Early-time thermalization of cosmic components? A hint for solving cosmic tensions

Hermano Velten, Ingrid Costa, and Winfried Zimdahl
Phys. Rev. D 104, 063507 – Published 3 September 2021

Abstract

We study an expanding two-fluid model of nonrelativistic dark matter and radiation, which are allowed to interact during a certain time span and to establish an approximate thermal equilibrium. Such an interaction, which generates an effective bulk viscous pressure at background level, is expected to be relevant for times around the transition from radiation to matter dominance. We quantify the magnitude of this pressure for dark-matter particle masses within the range 1eVmχ10eV around the matter-radiation equality epoch (i.e., redshift zeq3400) and demonstrate that the existence of a transient bulk viscosity has consequences which may be relevant for addressing current tensions of the standard cosmological model: (i) the additional (negative) pressure contribution modifies the expansion rate around zeq, yielding a larger H0 value, and (ii) large-scale structure formation is impacted by suppressing the amplitude of matter overdensity growth via a new viscous friction-term contribution to the Mészáros effect. As a result, the H0 and S8 tensions of the current standard cosmological model are both significantly alleviated.

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  • Received 14 April 2021
  • Accepted 15 August 2021

DOI:https://doi.org/10.1103/PhysRevD.104.063507

© 2021 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Hermano Velten1,*, Ingrid Costa2, and Winfried Zimdahl2

  • 1Departamento de Física, Universidade Federal de Ouro Preto (UFOP), Campus Universitário Morro do Cruzeiro, 35.400-000 Ouro Preto, Brazil
  • 2Núcleo COSMO-UFES and Departamento de Física, Universidade Federal do Espírito Santo (UFES), Avenida Fernando Ferrari s/n CEP 29.075-910, Vitória, Espírito Santo, Brazil

  • *Corresponding author. hermano.velten@ufop.edu.br

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Issue

Vol. 104, Iss. 6 — 15 September 2021

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