Abstract
Light scalar fields typically develop spatially varying backgrounds during inflation. Very often they do not directly affect the density perturbations, but interact with other fields that do leave nontrivial signals in primordial perturbations. In this sense they become “missing scalars” at the cosmological collider. We study potentially observable signals of these missing scalars, focusing on a special example where a missing scalar distorts the usual oscillatory features in the squeezed bispectrum. The distortion is also a useful signal distinguishing the de Sitter background induced thermal mass from a constant intrinsic mass.
Highlights
JHEP12(2021)098 the other hand, bosons with m < H can be copiously produced by inflationary expansion, irrespective of their SM couplings
It is often the case that we can’t see them directly today, either because they decay quickly in the thermal big-bang phase or because they are very weakly coupled.1. Even when they are coupled to the inflaton, the inflaton bispectrum mediated by these light scalar fields lacks the oscillatory signature like that mediated by heavier fields
The light scalar χ gives a space-dependent mass correction to σ, and it is this space-dependent mass that will leave a distinct signal in the inflaton correlator
Summary
Consider a simple model with two massive scalars, σ and χ, with a quartic coupling between them. The parameters mσ, mχ are defined to be the physically measured mass This means the loop-corrected two point function has the following large distance scaling. At each order in g, going from top to bottom is the second perturbative expansion in powers of m2χ/H2, where diagrams with more zero-mode χ propagators are enhanced compared to diagrams with the same topology but fewer zero-mode χ propagators. This is computationally advantageous, because the zero-mode χ propagator is a constant, χ(x)χ(y) zero mode. Which means diagrams with more zero-mode χ propagators are easier to calculate
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