Nonthermal neutrino-like hot dark matter in light of the $S_8$ tension

Subinoy Das , Anshuman Maharana , Vivian Poulin (1) , Ravi Kumar

1 LUPM - Laboratoire Univers et Particules de Montpellier

The $\mathrm{\Lambda }\mathrm{CDM}$ prediction of $S_8\equiv {\sigma }_8({\mathrm{\Omega }}_m/0.3{)}^{0.5}$—where ${\sigma }_8$ is the root mean square of matter fluctuations on an $8h^{-1}\mathrm{Mpc}$ scale—once calibrated on Planck cosmic microwave background data is $2-3\sigma$ lower than its direct estimate by a number of weak lensing surveys. In this paper, we explore the possibility that the “$S_8$ tension” is due to a fractional contribution of nonthermal hot dark matter (HDM) to the energy density of the Universe leading to a power suppression at small scales in the matter power spectrum. Any HDM model can be characterized by its effective mass $m_{\mathrm{sp}}^{\mathrm{eff}}$ and its contribution to the relativistic degrees of freedom at cosmic microwave background decoupling $\mathrm{\Delta }{N}_{\mathrm{eff}}$. Taking the specific example of a sterile particle produced from the decay of the inflaton during an early matter-dominated era, we find that the tension can be reduced below $2\sigma$ from Planck data only, but it does not favor a nonzero $\{m_{\mathrm{sp}}^{\mathrm{eff}},\mathrm{\Delta }{N}_{\mathrm{eff}}\}$. In combination with a measurement of $S_8$ from $\mathrm{KiDS}1000+\mathrm{BOSS}+2\mathrm{dfLenS}$, the $S_8$ tension would hint at the existence of a particle of mass $m_{\mathrm{sp}}^{\mathrm{eff}}\simeq 0.67_{-0.48}^{+0.26}\mathrm{eV}$ with a contribution to $\mathrm{\Delta }{N}_{\mathrm{eff}}\simeq 0.06\pm 0.05$. However, Pantheon and BOSS $\mathrm{BAO}/f{\sigma }_8$ data restricts the particle mass to $m_{\mathrm{sp}}^{\mathrm{eff}}\simeq 0.48_{-0.36}^{+0.17}$ and contribution to $\mathrm{\Delta }{N}_{\mathrm{eff}}\simeq 0.046_{-0.031}^{+0.004}$. We discuss implications of our results for other canonical nonthermal HDM models—the Dodelson-Widrow model and a hidden sector model of a thermal sterile particle with a different temperature. We report competitive results on such hidden sector temperature that might have interesting implications for particle physics model building, in particular connecting the $S_8$ tension to the longstanding short baseline oscillation anomaly.

Mots clés: matter: power spectrum; matter: fluctuation; cosmic background radiation: decoupling; energy: density; inflaton: decay; satellite: Planck; dark matter: hidden sector; dark matter: density; tension; sterile; cosmological model: parameter space; calibration; suppression; oscillation; fractional; buildings; thermal; anomaly

Domaines: Astrophysique [astro-ph]

Subinoy Das, Anshuman Maharana, Vivian Poulin, Ravi Kumar. Nonthermal neutrino-like hot dark matter in light of the $S_8$ tension. Physical Review D, 2022, 105 (10), pp.103503. ⟨10.1103/PhysRevD.105.103503⟩. ⟨hal-03203635⟩