Alleviating the Hubble tension with the $Λ_{ω_s}$CDM model

Abstract

We formulate a novel extension of the $Λ$CDM model, named $Λ_{ω_s}$CDM, in which we consider an additional term at early times in order to alleviate the Hubble tension. This additional component, referred to as \emph{matter with pressure}, indicates a barotropic fluid that is subdominant to dust and radiation as the Universe expands, thereby recovering the $Λ$CDM paradigm at late times. We constrain the $Λ_{ω_s}$CDM cosmology by performing a Markov Chain Monte Carlo analysis with Planck 2018 CMB, DESI DR2, and Pantheon+\texttt{SH0ES} data. The results suggest that the barotropic factor and the normalized density of the new fluid are given, respectively, by $ω_s=0.294_{-0.004(0.023)}^{+0.014(0.015)}$ and $10^{5}Ω_s=1.62_{-0.56(0.91)}^{+0.36(1.02)}$. With these two additional parameters, the Hubble constant is increased to $H_0 = 71.51^{+0.72(1.43)}_{-0.74(1.46)}$ km/s/Mpc, alleviating \emph{de facto} the Hubble tension.