CMB spectral distortions in generic two-field models

TL;DR

This paper explores how spectral distortions in the CMB can distinguish between different two-source primordial perturbation models, especially in mixed inflaton-curvaton scenarios, by analyzing their parameter space and potential observational constraints.

Contribution

It introduces a detailed parameterization of two uncorrelated sources affecting primordial perturbations and demonstrates how CMB spectral distortions can break degeneracies in curvaton models.

Findings

Spectral distortions can differentiate two-source models from single-source models.

Future measurements of $ ext{μ}$ and $r$ can constrain curvaton parameters.

The curvaton contribution is either negligible or dominant under current bounds.

Abstract

We investigate the CMB $\mu$ distortion in models where two uncorrelated sources contribute to primordial perturbations. We parameterise each source by an amplitude, tilt, running and running of the running. We perform a detailed analysis of the distribution signal as function of the model parameters, highlighting the differences compared to single-source models. As a specific example, we also investigate the mixed inflaton-curvaton scenario. We find that the $\mu$ distortion could efficiently break degeneracies of curvaton parameters especially when combined with future sensitivity of probing the tensor-to-scalar ratio $r$. For example, assuming bounds $\mu < 0.5 \times 10^{-8}$ and $r<0.01$, the curvaton contribution should either vanish or the curvaton should dominate primordial perturbations and its slow-roll parameter $\eta_{\chi}$ is constrained to the interval $-0.007 < \eta_{\chi}< 0.045$.