Light Particles with Spin in Inflation

Abstract

The existence of light particles with spin during inflation is prohibited by the Higuchi bound. This conclusion can be evaded if one considers states with a sizeable coupling with the inflaton foliation, since this breaks the de Sitter isometries. The action for these states can be constructed within the Effective Field Theory of Inflation, or using a CCWZ procedure. Light particles with spin have prescribed couplings with soft inflaton perturbations, which are encoded in consistency relations. We study the phenomenology of light states with spin 2. These mix with the graviton changing the tensor power spectrum and can lead to sizeable tensor non-Gaussianities. They also give rise to a scalar bispectrum and trispectrum with a characteristic angle-dependent non-Gaussianity.

Interferometer constraints on the inflationary field content

“…One proven way to scan all that is possible, at least from the late-time signatures perspective, is to employ an effective theory approach. We have done so by adopting the approach of [22] and focusing on the phenomenology corresponding to the presence of an extra spin-2 field. The key to a sufficiently large signal at small scales is choosing an appropriate time-dependence for the sound speed of the helicity-2 mode, c 2 (t).…”

“…It would be interesting to explore other possibilities for the functional form of c 2 ; we leave this to future work. It is important to stress that a considerable region of parameter space has not been ruled out by existing data, but by the requirement [22] that the dynamics does not run into a gradient instability. This goes to show that it is the interplay between model building & observational requirements to act as the most powerful filter towards a viable cosmology.…”

“…We take the parameter ρ to be a constant. The functions C ζ (ν) and C γ (ν) can be computed analytically for c 0 1 and c 2 1 [22] and are represented in Figs. (1) and (2) in the mass range ν ∈ [3/5, 7/5].…”

“…The massive s = 2 case is special in that a ghost-free fully non-linear formulation exists [16,17] and has been used in the context of inflation [18][19][20] (see also [21] and references therein for an approach with a related model). In this work we shall adopt a specific approach [22] to non-minimal coupling during inflation which is the natural generalization of the effective field theory (EFT) of single field (or clock) inflation of [23]. This is an EFT for the fluctuations around a given FLRW solution.…”

Constraining graviton non-Gaussianity through the CMB bispectra

“…Indeed, one particularly interesting setup where the power of symmetries manifests itself is in theories with higher spin fields. The possible signature of the presence of massive (or partially massless) fields during inflation has been extensively studied both theoretically [8][9][10][11][12][13][14][15][16] and observationally [17][18][19]. In fact, in the massless case, there are very strong theorems constraining the existence of HS fields in Minkowski spacetime (see no-go theorems [20][21][22]) which can be avoided in curved spacetime settings [23].…”