The holiest grail

TL;DR

This paper explores how B-mode polarization in the CMB can significantly improve constraints on primordial non-Gaussianity involving tensors and scalars, revealing new insights into early Universe physics.

Contribution

It demonstrates that BTT correlations in the CMB can provide constraints on primordial non-Gaussianity that surpass temperature-based methods by over an order of magnitude.

Findings

BTT measurements offer stronger constraints on tensor-scalar-scalar couplings.

B-mode non-Gaussianity probes early Universe physics beyond temperature anisotropies.

Significant information on primordial physics can be extracted from CMB B-mode polarization.

Abstract

I will discuss to what degree 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 $B$-mode polarization fluctuation with two temperature fluctuations (BTT). 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. I will 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. I will 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. BTT presents a measure of both primordial tensors and primordial non-Gaussianity, two of the most sought after signatures of the inflationary paradigm.