Dark Radiation with Baryon Acoustic Oscillations from DESI 2024 and the $H_0$ tension

Dark Radiation with Baryon Acoustic Oscillations from DESI 2024 and the $H_0$ tension
Itamar J. Allali, Alessio Notari, Fabrizio Rompineve
arXiv:2404.15220v1 Announce Type: new
Abstract: We investigate the presence of extra relativistic degrees of freedom in the early Universe, contributing to the effective number of neutrinos $N_text{eff}$, as $Delta N_text{eff}equiv N_text{eff}-3.044geq 0$, in light of the recent measurements of Baryon Acoustic Oscillations (BAO) by the DESI collaboration. We analyze one-parameter extensions of the $Lambda$CDM model where dark radiation (DR) is free streaming or behaves as a perfect fluid, due to self-interactions. We report a significant relaxation of upper bounds on $Delta N_text{eff}$, with respect to previous BAO data from SDSS+6dFGS, when additionally employing Planck data (and supernovae data from Pantheon+), setting $Delta N_text{eff}leq 0.39$ ($95%$ C.L.) for free streaming DR, and a very mild preference for fluid DR, $Delta N_text{eff} = 0.221^{+0.088}_{-0.18}$ ($leq 0.46$, $95%$ C.L.). Applying constraints from primordial element abundances leads to slightly tighter constraints on $Delta N_text{eff}$, but they are avoided if DR is produced after Big Bang Nucleosynthesis (BBN). For fluid DR we estimate the tension with the SH$_0$ES determination of $H_0$ to be around $(2.3-2.8)sigma$ level, and for free-streaming DR the tension is below $3sigma$ if production occurs after BBN. This lesser degree of tension motivates a combination with SH$_0$ES in these cases, resulting in a $4.4sigma-5sigma$ evidence for dark radiation with $Delta N_text{eff}simeq 0.6$ and large improvements in $chi^2$ over $Lambda$CDM, $-18lesssim Delta chi^2lesssim -25$.arXiv:2404.15220v1 Announce Type: new
Abstract: We investigate the presence of extra relativistic degrees of freedom in the early Universe, contributing to the effective number of neutrinos $N_text{eff}$, as $Delta N_text{eff}equiv N_text{eff}-3.044geq 0$, in light of the recent measurements of Baryon Acoustic Oscillations (BAO) by the DESI collaboration. We analyze one-parameter extensions of the $Lambda$CDM model where dark radiation (DR) is free streaming or behaves as a perfect fluid, due to self-interactions. We report a significant relaxation of upper bounds on $Delta N_text{eff}$, with respect to previous BAO data from SDSS+6dFGS, when additionally employing Planck data (and supernovae data from Pantheon+), setting $Delta N_text{eff}leq 0.39$ ($95%$ C.L.) for free streaming DR, and a very mild preference for fluid DR, $Delta N_text{eff} = 0.221^{+0.088}_{-0.18}$ ($leq 0.46$, $95%$ C.L.). Applying constraints from primordial element abundances leads to slightly tighter constraints on $Delta N_text{eff}$, but they are avoided if DR is produced after Big Bang Nucleosynthesis (BBN). For fluid DR we estimate the tension with the SH$_0$ES determination of $H_0$ to be around $(2.3-2.8)sigma$ level, and for free-streaming DR the tension is below $3sigma$ if production occurs after BBN. This lesser degree of tension motivates a combination with SH$_0$ES in these cases, resulting in a $4.4sigma-5sigma$ evidence for dark radiation with $Delta N_text{eff}simeq 0.6$ and large improvements in $chi^2$ over $Lambda$CDM, $-18lesssim Delta chi^2lesssim -25$.