Constraining the inflationary potential with spectral distortions

TL;DR

Spectral distortions of the CMB can significantly improve constraints on inflationary models and the primordial power spectrum, especially when combined with current and future anisotropy experiments, extending the probed parameter space.

Contribution

This work demonstrates how combining spectral distortion measurements with anisotropy data can substantially tighten constraints on inflationary models, using updated numerical tools and foreground marginalization.

Findings

SD experiments tighten inflationary constraints by up to 640%.

Adding SD data increases the figure of merit by up to 1600.

Forecasts show significant improvements with future missions like PIXIE and PRISM.

Abstract

Measuring spectral distortions (SDs) of the cosmic microwave background (CMB) will provide new constraints on previously unexplored scales of the primordial power spectrum, allowing us to extend the probed parameter space by several orders of magnitude in $k$-space, which could have significant implications in the context of primordial black holes and gravitational waves, among others. Here we discuss how various models of inflation can be tightly constrained by the combination of current and future CMB SD and anisotropy experiments. In particular, we investigate the constraining power of SD experiments such as FIRAS, PIXIE, and PRISM in conjunction with CMB anisotropy probes such as Planck or CMB-S4 plus LiteBIRD. Building on the latest version of the Boltzmann solver CLASS (v3.0), here we also consistently marginalize over the possible galactic and extra-galactic foregrounds for the SD missions. With this numerical setup, we are able to realistically forecast the improvements that the increased lever-arm provided by the addition of the various SD missions will bring for several combinations of the aforementioned experiments. As a result, in all considered models we observe that SDs provide a highly significant tightening of the constraints by up to 640%, and increase the figure of merit up to a factor of around 1600.