Searching for sterile neutrinos in dynamical dark energy cosmologies
Lu Feng, Jing-Fei Zhang, Xin Zhang
TL;DR
The paper investigates how dynamical dark energy models affect cosmological limits on sterile neutrinos, comparing ΛCDM+$\\nu_s$, $w$CDM+$\\nu_s$, and HDE+$\\nu_s$ using Planck 2015 data plus low-redshift probes with fixed active-neutrino sum $\\sum m_\\nu=0.06$ eV and varying $N_{\\rm eff}$ and $m_{\\nu,{\\rm sterile}}^{\\rm eff}$. It employs CosmoMC for MCMC sampling and uses AIC for model comparison, finding that without growth data only upper limits can be derived, e.g., for Planck+BAO+SN+$H_0$+lensing the bounds are $m_{\\nu,{\\rm sterile}}^{\\rm eff}<0.2675$ eV (ΛCDM), $<0.5313$ eV (wCDM), and $<0.1989$ eV (HDE), with corresponding $N_{\\rm eff}$ limits. The results show $N_{\\rm eff}$ correlates positively with $H_0$, and the dark-energy model materially shifts the sterile-neutrino limits: the $w$CDM case loosens the mass bound while the HDE case tightens it, though HDE is not favored by the overall fit (large ΔAIC) despite easing the $H_0$ tension. The study highlights that dark-energy properties can significantly influence sterile-neutrino constraints and the interpretation of potential extra relativistic species in cosmology.
Abstract
We investigate how the dark energy properties change the cosmological limits on sterile neutrino parameters by using recent cosmological observations. We consider the simplest dynamical dark energy models, the $w$CDM model and the holographic dark energy (HDE) model, to make an analysis. The cosmological observations used in this work include the Planck 2015 CMB temperature and polarization data, the baryon acoustic oscillation data, the type Ia supernova data, the Hubble constant direct measurement data, and the Planck CMB lensing data. We find that, $m_{ν,{\rm{sterile}}}^{\rm{eff}}<0.2675$ eV and $N_{\rm eff}<3.5718$ for $Λ$CDM cosmology, $m_{ν,{\rm{sterile}}}^{\rm{eff}}<0.5313$ eV and $N_{\rm eff}<3.5008$ for $w$CDM cosmology, and $m_{ν,{\rm{sterile}}}^{\rm{eff}}<0.1989$ eV and $N_{\rm eff}<3.6701$ for HDE cosmology, from the constraints of the combination of these data. Thus, without the addition of measurements of growth of structure, only upper limits on both $m_{ν,{\rm{sterile}}}^{\rm{eff}}$ and $N_{\rm eff}$ can be derived, indicating that no evidence of the existence of a sterile neutrino species with eV-scale mass is found in this analysis. Moreover, compared to the $Λ$CDM model, in the $w$CDM model the limit on $m_{ν,{\rm{sterile}}}^{\rm{eff}}$ becomes much looser, but in the HDE model the limit becomes much tighter. Therefore, the dark energy properties could significantly influence the constraint limits of sterile neutrino parameters.