Cosmological constraints on extra radiation and early dark energy with lepton asymmetry and varying quark masses

Abstract

We investigate cosmological constraints on extra radiation and axionlike early dark energy (EDE), allowing primordial lepton asymmetry or light-quark-mass variation during big bang nucleosynthesis (BBN). We combine Planck CMB, DESI DR2 BAO, Pantheon+ supernovae, and primordial helium and deuterium measurements. When both extra radiation and lepton asymmetry are allowed, we obtain $N_{\rm eff}=3.27\pm0.16$, $ξ=0.017\pm0.011$, and $H_0=69.24\pm0.92\,{\rm km\,s^{-1}\,Mpc^{-1}}$. A positive lepton asymmetry compensates the helium increase caused by extra radiation, allowing a higher inferred Hubble constant even with the LBT helium measurement, which agrees with standard BBN. For EDE, primordial-abundance measurements instead restrict the higher baryon densities associated with larger EDE fractions, which reduce the predicted deuterium abundance. Allowing lepton asymmetry does not relax this restriction. In contrast, a positive light-quark-mass variation increases deuterium and compensates this reduction, permitting larger EDE fractions and a higher inferred Hubble constant. The same variation leaves the extra-radiation constraint nearly unchanged. We also find that allowing lepton asymmetry relaxes the 95\% upper limit on the summed neutrino mass from $0.0640\,{\rm eV}$ to $0.0777\,{\rm eV}$ in the extra-radiation model.