Distinguishing different scenarios of early energy release with spectral distortions of the cosmic microwave background

TL;DR

Future precise measurements of the CMB spectrum could significantly enhance our understanding of the early universe, potentially detecting or ruling out various particle decay and dissipation scenarios with unprecedented sensitivity.

Contribution

This paper demonstrates the potential of PIXIE-like spectrometers to vastly improve constraints on early-universe energy release scenarios through spectral distortion measurements.

Findings

PIXIE can improve constraints on spectral distortions by over three orders of magnitude.

Potential to detect signatures of relic particle annihilation and decay.

Future experiments could further enhance sensitivity to pre-recombination processes.

Abstract

Deviations of the cosmic microwave background (CMB) frequency spectrum from a pure blackbody tell an exciting story about the thermal history of our Universe. In this paper we illustrate how well future CMB measurements might decipher this tale, envisioning a PIXIE-like spectrometer, which could improve the distortion constraints obtained with COBE/FIRAS some 20 years ago by at least three orders of magnitude. This opens a large discovery space, offering deep insights to particle and early-universe physics, opportunities that no longer should be left unexplored. Specifically, we consider scenarios with annihilating and decaying relic particles, as well as signatures from the dissipation of primordial small-scale power. PIXIE can potentially rule out different early-universe scenarios, and moreover will allow unambiguous detections in many of the considered cases, as we demonstrate here. We also discuss slightly more futuristic experiments, with several times improved sensitivities, to highlight the large potential of this new window to the pre-recombination universe.