How Thermal Inflation can save Minimal Hybrid Inflation in Supergravity

Abstract

Minimal hybrid inflation in supergravity has been ruled out by the 2015 Planck observations because the spectral index of the produced curvature perturbation falls outside observational bounds. To resurrect the model, a number of modifications have been put forward but many of them spoil the accidental cancellation that resolves the eta-problem and require complicated Kahler constructions to counterbalance the lost cancellation. In contrast, in this paper the model is rendered viable by supplementing the scenario with a brief period of thermal inflation, which follows the reheating of primordial inflation. The scalar field responsible for thermal inflation requires a large non-zero vacuum expectation value (VEV) and a flat potential. We investigate the VEV of such a flaton field and its subsequent effect on the inflationary observables. We find that, for large VEV, minimal hybrid inflation in supergravity produces a spectral index within the 1-sigma Planck bound and a tensor-to-scalar ratio which may be observable in the near future. The mechanism is applicable to other inflationary models.

9 pages, 1 figure, published version

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• Small-scale Effects of Thermal Inflation on Halo Abundance at High-$z$, Galaxy Substructure Abundance and 21-cm Power Spectrum
• Thermal curvature perturbations in thermal inflation
• Thermal Inflation with a Thermal Waterfall Scalar Field Coupled to a Light Spectator Scalar Field
• O'R Inflation in $F$-term Supergravity
• Hybrid Inflation in Quasi-minimal Supergravity with Monotonic Inflationary Potentia