Partially massless fields during inflation

Abstract

The representation theory of de Sitter space allows for a category of partially massless particles which have no flat space analog, but could have existed during inflation. We study the couplings of these exotic particles to inflationary perturbations and determine the resulting signatures in cosmological correlators. When inflationary perturbations interact through the exchange of these fields, their correlation functions inherit scalings that cannot be mimicked by extra massive fields. We discuss in detail the squeezed limit of the tensor-scalar-scalar bispectrum, and show that certain partially massless fields can violate the tensor consistency relation of single-field inflation. We also consider the collapsed limit of the scalar trispectrum, and find that the exchange of partially massless fields enhances its magnitude, while giving no contribution to the scalar bispectrum. These characteristic signatures provide clean detection channels for partially massless fields during inflation. arXiv:1712.06624v2 [hep-th] 21 Apr 20181 In order to write a local theory with the right number of degrees of freedom, one imposes a gauge symmetry that must be obeyed by the higher-spin Lagrangian. It turns out to be hard to find self-consistent interacting theories of these degrees of freedom. It might be that a single light degree of freedom in the spectrum implies the existence of many other higher-spin degrees of freedom. An extreme example of this is the occurrence of infinitely many fields in the Vasiliev theory of massless higher-spin particles in (A)dS [12,13]. Similarly, interacting theories of an infinite tower of partially massless fields were studied in [14][15][16][17][18].

Bootstrapping inflationary correlators in Mellin space

“…(4.77) 40 In particular, for d = 3, tree-exchanges of conformally coupled and massless scalars are given by (Di)-Logarithms in the momenta [29,36], while exchanges of (partially)-massless fields (which are further constrained by the corresponding gauge-symmetries) have been observed to be given by rational functions of the momenta [34,36,37,41,104,123]. 41 I.e.…”

“…− Li 2 1 − p 34 Exchange of massless scalar. The exchange of a massless scalar in d = 3 presents an interesting example.…”

“…Cosmological observations can be traced back to spatial correlations of primordial fluctuations at the end of inflation, which lie on the boundary of an (approximate) de Sitter space-time. Non-Gaussianities in primordial correlation functions encode the physics of inflation, including interactions and field content, and the ultimate goal of the "Cosmological Collider Physics" programme [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] is to classify the possible shapes of non-Gaussianities for comparison with observations. To this end it is important to develop new tools to systematically carve out the shapes of non-Gaussianities generated by a given spectrum and couplings.…”

Cosmological collider physics and the curvaton

“…Through a careful measurement of such dependencies, one can infer the mass and spin of such heavy particles-a rare opportunity to probe on-shell physics at very high energy scales. This is the focus of the "cosmological collider physics" program [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. For various recent ideas in this direction see, [18][19][20][21][22][23][24][25][26][27][28].…”

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].…”