Spectro-spatial evolution of the CMB III: transfer functions, power spectra and Fisher forecasts

Understand

In this paper, we provide the first computations for the distortion transfer functions of the cosmic microwave background (CMB) in the perturbed Universe, following up on paper I and II in this series.

• We illustrate the physical effects inherent to the solutions, discussing and demonstrating various limiting cases for the perturbed photon spectrum.
• We clarify the relationship between distortion transfer functions and the photon spectrum itself, providing the machinery that can then compute constrainable CMB signal power spectra including spectral distortions for single energy injection and decaying particle scenarios.
• Our results show that the $\mu \times T$ and $y\times T$ power spectra reach levels that can be constrained with current and future CMB experiments without violating existing constraints from COBE/FIRAS.