Tilt of primordial gravitational wave spectrum in a universe with sterile neutrinos

Abstract

In this work, we constrain the spectral index $n_t$ of the primordial gravitational wave power spectrum in a universe with sterile neutrinos by using the Planck temperature data, the WMAP 9-year polarization data, the baryon acoustic oscillation data, and the BICEP2 data. We call this model the $\Lambda$CDM+$r$+${\nu }_s$+$n_t$ model. The additional massive sterile neutrino species can significantly relieve the tension between the Planck and BICEP2 data, and thus can reduce the possible effects of this tension on the fit results of $n_t$. To constrain the parameters of sterile neutrino, we also utilize the Hubble constant direct measurement data, the Planck Sunyaev-Zeldovich cluster counts data, the Planck CMB lensing data, and the cosmic shear data. We find that due to the fact that the BICEP2 data are most sensitive to the multipole $\ell \sim 150$ corresponding to $k\sim 0.01$ Mpc${}^{-1}$, there exists a strong anticorrelation between $n_t$ and $r_{0.002}$ in the BICEP2 data, and this further results in a strongly blue-tilt spectrum. However, a slightly red-tilt tensor power spectrum is also allowed by the BICEP2 data in the region with larger value of $r_{0.002}$. By using the full data sets, we obtain $m_{\nu ,\mathrm{sterile}}^{\mathrm{eff}}=0.48_{-0.13}^{+0.11}$ eV, $N_{\mathrm{eff}}=3.73_{-0.37}^{+0.34}$, and $n_t=0.96_{-0.63}^{+0.48}$ for the $\Lambda$CDM+$r$+${\nu }_s$+$n_t$ model.

5 pages, 3 figures, 1 table; published in Sci China-Phys Mech Astron (Special Topic: BICEP2 and Beyond)

Cited by in corpus (8)

• Neutrinos in the holographic dark energy model: constraints from latest measurements of expansion history and growth of structure
• Neutrinos and dark energy after Planck and BICEP2: data consistency tests and cosmological parameter constraints
• Measuring growth index in a universe with sterile neutrinos
• Probing $f(R)$ cosmology with sterile neutrinos via measurements of scale-dependent growth rate of structure
• A search for sterile neutrinos in interacting dark energy models using DESI baryon acoustic oscillations and DES supernovae data
• Pre-inflationary genesis with CMB B-mode polarization
• Quantifying the impact of future Sandage-Loeb test data on dark energy constraints
• Prospects for searching for sterile neutrinos with gravitational wave and $\gamma$-ray burst joint observations