Alleviating the $H_0$ tension in Rastall gravity

Abstract

The persistent discrepancy between local determinations of the Hubble constant $H_0$ and the Planck 2018 value ($67.4 \pm 0.5~{\rm km\,s^{-1}\,Mpc^{-1}}$) within $Λ$CDM remains a central challenge in precision cosmology. We investigate the Hubble tension in $Λ$CDM and its Rastall extension (R-$Λ$CDM) for flat, open, and closed geometries. We analyze three primary dataset combinations: D$_1$ (late-time probes: SN + $H(z)$ + $fσ_8$), D$_2$ (late-time probes combined with DESI DR2 BAO and BBN), and D$_3$ (late-time probes combined with BAO and Planck 2018 CMB distance priors). Parameters are constrained via Markov Chain Monte Carlo sampling, and tensions with SH0ES ($73.2 \pm 1.3~{\rm km\,s^{-1}\,Mpc^{-1}}$) and Planck are expressed in units of the combined uncertainty. In addition, we include a Planck-only configuration (D$_4$) as a reference baseline to isolate early-Universe constraints on $H_0$. Within $Λ$CDM, D$_1$ and D$_2$ yield $H_0 \simeq 70.75$-$71.43~{\rm km\,s^{-1}\,Mpc^{-1}}$, reducing the SH0ES discrepancy to $1.11σ$--$1.63σ$ while maintaining a $3.62σ$-$4.23σ$ tension with Planck. Including CMB distance priors (D$_3$) shifts the result to $H_0 \simeq 67.18$--$67.55~{\rm km\,s^{-1}\,Mpc^{-1}}$, consistent with Planck at $0.09σ$-$0.38σ$ but increasing the SH0ES discrepancy to $4.25σ$-$4.51σ$.