Gravitational modulated reheating and non-Gaussianity in Supergravity R^2 inflation

TL;DR

This paper explores how flat directions in supersymmetric theories can modulate reheating after R^2 inflation, leading to specific predictions for non-Gaussianity, spectral index, and tensor-to-scalar ratio.

Contribution

It introduces a novel mechanism of modulated reheating in supergravity R^2 inflation caused by quantum fluctuations of flat directions, affecting curvature fluctuations.

Findings

Spectral index between 0.960 and 0.983

Local non-Gaussianity parameter f_nl around ±10

Tensor-to-scalar ratio r less than 4×10^{-3}

Abstract

Reheating after R^2 inflation proceeds through gravitational particle production of conformally noninvariant fields. We argue that the nonvanishing expectation value of flat directions generic in supersymmetric theories break conformal invariance of the fields coupled to them in a position-dependent manner due to quantum fluctuations. As a result modulated reheating can occur after the supergravity R^2-inflation. The resultant curvature fluctuation is a mixture of the one produced during inflation and that produced by modulated reheating. The spectral index takes a value between n_s=0.960 and 0.983, the nonlinearity parameter of the local-type non-Gaussianity can be f_nl\sim \pm 10, and the tensor-to-scalar ratio is r \le 4\times 10^{-3}.