Challenges and prospects for better measurements of the CMB intensity spectrum

TL;DR

This paper proposes a novel method for detecting CMB spectral distortions by measuring the frequency derivative of the CMB temperature across large frequency ranges, aiming to improve upon previous absolute measurement techniques.

Contribution

It introduces a new observational approach focusing on frequency derivatives and foreground measurements, enhancing prospects for detecting CMB spectral distortions.

Findings

Current methods have failed to detect distortions.

Measuring the frequency derivative offers a promising alternative.

Future observations from ground and space could succeed.

Abstract

Spectral distortions of the Cosmic Microwave Background (CMB) offer the possibility of probing processes which occurred during the evolution of our Universe going back up to Z$\simeq 10^7$. Unfortunately all the attempts so far carried out for detecting distortions failed. All of them were based on comparisons among absolute measurements of the CMB temperature at different frequencies. We suggest a different approach: measurements of the frequency derivative of the CMB temperature over large frequency intervals instead of observations of the absolute temperature at few, well separated, frequencies as frequently done in the past, and, direct measurements of the foregrounds which hinder bobservations, at the same site and with the same radiometer prepared for the search of CMB distortions. We discuss therefore the perspectives of new observations in the next years from the ground, at very special sites, or in space as independent missions or part of other CMB projects