Non-Gaussianities in generalized non-local R2-like inflation

Author:

Koshelev Alexey S.,Kumar K. Sravan,Starobinsky Alexei A.

Abstract

Abstract In [1], a most general higher curvature non-local gravity action was derived that admits a particular R2-like inflationary solution predicting the spectral index of primordial scalar perturbations $$ {n}_s(N)\approx 1-\frac{1}{2} $$ n s N 1 1 2 , where N is the number of e-folds before the end of inflation, N ≫ 1, any value of the tensor-to-scalar ratio r(N) < 0.036 and the tensor tilt nt(N) violating the r = –8nt condition. In this paper, we compute scalar primordial non-Gaussianities (PNGs) in this theory and effectively demonstrate that higher curvature non-local terms lead to reduced bispectrum fNL (k1, k2, k3) mimicking several classes of scalar field models of inflation known in the literature. We obtain |fNL| ~ O(1 – 10) in the equilateral, orthogonal, and squeezed limits and the running of these PNGs measured by the quantity $$ \left|\frac{d\ln {f}_{\textrm{NL}}}{d\ln k}\right|\lesssim 1 $$ d ln f NL d ln k 1 . Such PNGs are sufficiently large to be measurable by future CMB and Large Scale Structure observations, thus providing a possibility to probe the nature of quantum gravity. Furthermore, we demonstrate that the R2-like inflation in non-local modification of gravity brings non-trivial predictions which go beyond the current status of effective field theories (EFTs) of single field, quasi-single field and multiple field inflation. A distinguishable feature of non-local R2-like inflation compared to local EFTs is that we can have running of PNGs at least an order of magnitude higher. In summary, through our generalized non-local R2-like inflation, we obtain a robust geometric framework of inflation that can explain any detection of observable quantities related to scalar PNGs.

Publisher

Springer Science and Business Media LLC

Subject

Nuclear and High Energy Physics

Reference68 articles.

1. A.S. Koshelev, K.S. Kumar and A.A. Starobinsky, Generalized non-local R2-like inflation, accepted for publication in JHEP [arXiv:2209.02515] [INSPIRE].

2. A.A. Starobinsky, A new type of isotropic cosmological models without singularity, Phys. Lett. B 91 (1980) 99 [INSPIRE].

3. A.A. Starobinsky, Nonsingular model of the universe with the quantum gravitational de Sitter stage and its observational consequences, in the proceedings of the Second seminar on quantum gravity, Moscow, October 1981, INR Press, Moscow, U.S.S.R. (1982), p. 58 [INSPIRE].

4. A.A. Starobinsky, The perturbation spectrum evolving from a nonsingular initially de-Sitter cosmology and the microwave background anisotropy, Sov. Astron. Lett. 9 (1983) 302 [INSPIRE].

5. A. Vilenkin, Classical and quantum cosmology of the Starobinsky inflationary model, Phys. Rev. D 32 (1985) 2511 [INSPIRE].

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