FOSSIL: A future mission for CMB spectral distortion measurements

FOSSIL is a proposed space mission designed to deliver unprecedented absolute spectroscopic measurements of the sky intensity over a broad frequency range from 50 GHz to 2 THz, in order to accurately measure chemical-potential mu-type, Compton y-type, and Compton relativistic y-type CMB spectral distortions.

The mission is intended to reach monopole sensitivities representing a gain of roughly three orders of magnitude over COBE/FIRAS. These capabilities would allow constraints on primordial density fluctuations on scales of k ~ 10 to 10^4 Mpc^-1, tests of inflationary models, probes of dark matter annihilation, decay, and interactions, constraints on primordial black hole seed scenarios, and pinning down of feedback models in galaxy evolution and structure formation by measuring the cosmic thermal energy content.

FOSSIL's 130 spectral channels would also enable legacy astrophysics, including precise characterization of the Cosmic Infrared Background, line intensity mapping during cosmic noon, and detailed Galactic dust mapping.