Measuring primordial anisotropic correlators with CMB spectral distortions

TL;DR

This paper proposes that inflationary models with broken rotational symmetry can produce detectable off-diagonal correlations between CMB spectral distortions and temperature fluctuations, revealing primordial anisotropies.

Contribution

It introduces a method to detect primordial anisotropic signals via $bc$-type spectral distortions correlated with temperature fluctuations in the CMB.

Findings

Quadrupolar bispectrum asymmetry leads to nonzero $bc$-$T$ correlation.

Spectral distortions can detect small-scale primordial fluctuations.

High signal-to-noise ratio achievable with cosmic variance limited experiments.

Abstract

We show that inflationary models with broken rotational invariance generate testable off-diagonal signatures in the correlation between the $\mu$-type distortion and temperature fluctuations of the cosmic microwave background. More precisely, scenarios with a quadrupolar bispectrum asymmetry, usually generated by fluctuations of primordial vector fields, produce a nonvanishing $\mu$-$T$ correlation when $|\ell_1-\ell_2|=2$. Since spectral distortions are sensitive to primordial fluctuations up to very small scales, a cosmic variance limited spectral distortion experiment can detect such effects with a high signal-to-noise ratio.