https://doi.org/10.1140/epjs/s11734-025-01863-x
Regular Article
Preheating and gravitational waves in large-field hilltop inflation
Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, 500032, Hyderabad, India
Received:
15
July
2025
Accepted:
12
August
2025
Published online:
18
August
2025
The combined Planck, BICEP/Keck Array and BAO measurements of the scalar spectral index and the tensor-to-scalar ratio from the cosmic microwave background observations severely constrain or completely rule out several models of inflationary potentials. On the other hand, the data seems to favor concave potentials over convex ones. In this paper, we study preheating and gravitational waves after inflation in a large-field, regularized hilltop potential where inflation takes place in the concave plateau. The inflaton, 
, is coupled to a subdominant scalar field, 
, through a quartic coupling. After inflation ends, oscillates about the potential minimum and becomes inhomogeneous. The growth of the fluctuation modes, 
and 
, on a homogeneous oscillating background is analyzed in linear perturbation theory, revealing that small modes likely experience broad self-resonance or external parametric resonance. To determine if the resonances are sufficiently strong to cause unstable growth of the modes we perform a lattice simulation. The lattice simulations demonstrate that, although the initial inhomogeneities generate a stochastic gravitational wave background that remains below the present observational limit, the fluctuations do not grow exponentially, and the occupation numbers of and remain close to zero.
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© The Author(s), under exclusive licence to EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature 2025
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
