CMBB-mode non-Gaussianity

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 BT T 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.

Non-Gaussianity as a particle detector

“…-We quantify the size of the tensor-scalar-scalar bispectrum by 42) where the bispectrum is evaluated in the equilateral configuration, k 1 = k 2 = k 3 ≡ k, with vectors maximally aligned with the polarization tensor. This choice of normalization agrees with that adopted in [58] and implies f γζζ NL = √ r/16 for single-field slow-roll inflation [12].…”

“…This signal may be observable in the BT T correlator of CMB anisotropies [58]. 22 A deviation from the leading term of the consistency relation due to spinning particles can arise in a number of ways: first, the unitarity bound can be evaded if the de Sitter isometries are not fully respected in the quadratic action of the spinning field [60,61].…”

“…While the size of the single-exchange diagram is strongly constrained by naturalness, both the diagrams [(e,f)] can lead to naturally large non-Gaussianity, as in the case of the scalar bispectrum. Future constraints on f γζζ NL from observations of the BT T correlator of CMB anisotropies were discussed in [58]. The proposed CMB Stage IV experiments [59] will have the sensitivity to reach σ( √ rf γζζ NL ) ∼ 0.1, which suggests that the tensor non-Gaussianity due to massive spinning particles might be detectable for r 10…”

Prospects for cosmological collider physics

“…These constraints will be extended to those including the CMB B-modes sourced by tensor non-Gaussianities [29,32] and a more exhaustive search will be performed to include recently-developed models (e.g. [24,33]).…”

In search of large signals at the cosmological collider

“…In the coming decades, much more observational data will further shed light in this era. In particular, the precision in the primordial Non-Gaussianity (NG) measurement will be improved by orders of magnitudes [1]. Among various NG observables, the oscillatory shape in the squeezed limit due to particle production during the inflation is particularly striking.…”