On CMB B-Mode Non-Gaussianity

TL;DR

This paper demonstrates that analyzing the B-mode polarization in the CMB can significantly improve constraints on primordial non-Gaussianity involving tensor and scalar fluctuations, revealing new insights into early universe physics.

Contribution

It introduces the use of the TT correlation to better constrain tensor-scalar-scalar primordial bispectra, surpassing temperature-only measurements.

Findings

TT correlation provides over ten times better constraints than temperature alone.

B-mode non-Gaussianity offers a new window into primordial physics.

Experiment like CMB-Stage IV can significantly improve detection sensitivity.

Abstract

We study the degree to which the cosmic microwave background (CMB) can be used to constrain primordial non-Gaussianity involving one tensor and two scalar fluctuations, focusing on the correlation of one polarization $B$ mode with two temperature modes. In the simplest models of inflation, the tensor-scalar-scalar primordial bispectrum is non-vanishing and is of the same order in slow-roll parameters as the scalar-scalar-scalar bispectrum. We calculate the $\langle BTT\rangle$ correlation arising from a primordial tensor-scalar-scalar bispectrum, and show that constraints from an experiment like CMB-Stage IV using this observable are more than an order of magnitude better than those on the same primordial coupling obtained from temperature measurements alone. We argue that $B$-mode non-Gaussianity opens up an as-yet-unexplored window into the early Universe, demonstrating that significant information on primordial physics remains to be harvested from CMB anisotropies.