Forecasting sensitivity on tilt of power spectrum of primordial gravitational waves after Planck satellite

TL;DR

This paper forecasts the future sensitivity of various CMB experiments to the tilt of the primordial gravitational wave spectrum, considering foreground contamination, and finds that satellite experiments can measure the tilt with reasonable precision.

Contribution

It provides a comprehensive Fisher matrix forecast for the sensitivity of multiple upcoming CMB experiments to the tensor tilt, accounting for foregrounds and current constraints.

Findings

Satellite experiments can measure the tensor tilt with $\sigma_{n_t}\lesssim0.1$ for $r\gtrsim2 imes10^{-3}$.

Ground-based and balloon experiments have worse sensitivity to the tensor tilt.

Current constraints prevent testing the inflationary consistency relation $n_t=-r/8$ with these experiments.

Abstract

By taking into account the contamination of foreground radiations, we employ the Fisher matrix to forecast the future sensitivity on the tilt of power spectrum of primordial tensor perturbations for several ground-based (AdvACT, CLASS, Keck/BICEP3, Simons Array, SPT-3G), balloon-borne (EBEX, Spider) and satellite (CMBPol, COrE, LiteBIRD) experiments of B-mode polarizations. For the fiducial model $n_t=0$, our results show that the satellite experiments give good sensitivity on the tensor tilt $n_t$ to the level $\sigma_{n_t}\lesssim0.1$ for $r\gtrsim2\times10^{-3}$, while the ground-based and balloon-borne experiments give worse sensitivity. By considering the BICEP2/Keck Array and Planck (BKP) constraint on the tensor-to-scalar ratio $r$, we see that it is impossible for these experiments to test the consistency relation $n_t=-r/8$ in the canonical single-field slow-roll inflation models.