CMB Spectral Distortions: The HOW, WHAT, and WHEN?

Bryce Cyr (MIT)

March 09, 2026

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Abstract: In this talk, I will boldly attempt to cover the formalism, applications, and experimental prospects of future CMB spectrometers, aimed at measuring small deviations to the blackbody nature of the cosmic microwave background. I will begin with a gentle introduction to the cosmological thermalization problem, providing general motivation from both within and outside of the so-called standard models of cosmology and particle physics. Following this, I will show how current experimental data (from the 1990’s) can be used to constrain dark photons and dark atomic sectors, highlighting the potential gain in sensitivity that would come from a next-generation experiment such as FOSSIL or PIXIE. Finally, I will conclude with an overview of the experimental landscape, which after over two decades of inactivity, has had a flurry of exciting recent developments.