Constraining light sterile neutrino mass with the BICEP2/Keck Array 2014 B-mode polarization data

TL;DR

This paper constrains the mass of light sterile neutrinos using cosmological data, including recent B-mode polarization measurements from BICEP2/Keck, finding tighter bounds and implications for sterile neutrino models.

Contribution

It provides new constraints on sterile neutrino mass by incorporating the latest B-mode polarization data, improving upon previous bounds and exploring tensions with other cosmological measurements.

Findings

Inclusion of BK14 data slightly strengthens sterile neutrino mass constraints.

The bound on sterile neutrino mass is tightened to less than 0.28 eV with combined datasets.

Fully thermalized sterile neutrinos around 1 eV are disfavored by the data.

Abstract

We explore the thermal light sterile neutrino situation from cosmological perspective in the $\Lambda \textrm{CDM} + r_{0.05} + N_{\textrm{eff}} + m^{\textrm{eff}}_{\textrm{s}}$ model using combinations of latest data sets available. Here, $r_{0.05}$ is the tensor-to-scalar ratio at the pivot scale of $k_*=0.05h$ Mpc$^{-1}$, $N_{\textrm{eff}}$ is the effective number of relativistic species during recombination, and $m^{\textrm{eff}}_{\textrm{s}}$ is the effective mass of the sterile neutrino. Among Cosmic Microwave Background (CMB) datasets, we use Planck 2015 temperature and low-$l$ ($l <$ 30) polarization data and the latest data release on the B-mode polarization up to and including 2014 from the BICEP2/Keck collaboration (BK14). We also use the latest BAO data from SDSS-III BOSS DR12, MGS, and 6dFS; and a Gaussian prior (HST) on the Hubble constant ($H_0 = 73.24 \pm 1.74$ km/sec/Mpc) from direct measurements. We find that inclusion of BK14 data makes the constraints on the effective mass of sterile neutrino ($m^{\textrm{eff}}_{\textrm{s}}$) slightly stronger by preferring higher $\sigma_8$ values. The bound of $m^{\textrm{eff}}_{\textrm{s}} <$ 0.46 eV (95\% C.L.) is found for the combination of Planck 2015, BAO and BK14 datasets, whereas the bound is $m^{\textrm{eff}}_{\textrm{s}} <$ 0.53 eV (95\% C.L.) without the BK14 data. Our most aggressive bound of $m^{\textrm{eff}}_{\textrm{s}} <$ 0.28 eV (95\% C.L.) is obtained with Planck 2015, HST and BK14. However, the HST prior also leads to very high $N_{\textrm{eff}}$ which might be in conflict with bounds from BBN. Our analysis indicates that fully thermalized sterile neutrinos with mass $\sim 1$ eV are slightly more disfavoured with the inclusion of BK14 data. It also seems to make the agreement between Planck 2015 and CFHTLenS (weak gravitational lensing data) worse due to the higher $\sigma_8$ values (abstract abridged).