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Curvaton-assisted hilltop inflation

Wen-Yuan Ai1,2,*, Stephen F. King3,†, Xin Wang3,4,5,‡, and Ye-Ling Zhou6,§

  • 1State Key Laboratory of Dark Matter Physics, Tsung-Dao Lee Institute and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 201210, China
  • 2Key Laboratory for Particle Astrophysics and Cosmology (MOE), and Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University, Shanghai 201210, China
  • 3School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom
  • 4Dipartimento di Fisica e Astronomia “Galileo Galilei,” Università degli Studi di Padova, Via Francesco Marzolo 8, 35131 Padova, Italy
  • 5INFN, Sezione di Padova, Via Francesco Marzolo 8, 35131 Padova, Italy
  • 6School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, UCAS, Hangzhou 310024, China

  • *Contact author: wenyuanai@sjtu.edu.cn
  • †Contact author: king@soton.ac.uk
  • ‡Contact author: xin.wang@unipd.it
  • §Contact author: zhouyeling@ucas.ac.cn
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Phys. Rev. D 114, 076002 – Published 1 October, 2026

DOI: https://doi.org/10.1103/gbgy-7fkl

Abstract

Following the recent Atacama Cosmology Telescope results, we consider hilltop inflation where the inflaton is coupled to a curvaton, simultaneously addressing two main challenges faced by conventional hilltop inflation models: the initial-value problem; and their viability for sub-Planckian field values. In standard single-field hilltop inflation, the inflaton must start extremely close to the maximum of the potential, raising concerns about the naturalness of the initial conditions. We demonstrate that the curvaton field not only significantly relaxes the initial-value tuning required for hilltop inflation but also opens up parameter space through modifying the curvature perturbation power spectrum, reviving the quartic hilltop inflation model in the sub-Planckian regime. We find viable parameter space consistent with the recent cosmological observations.

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Phys. Rev. D 114, 076002– Published 1 October, 2026
  • Received 20 May 2026
  • Accepted 3 September 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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