Curvaton-assisted hilltop inflation

TL;DR

This paper explores how coupling a curvaton to hilltop inflation models relaxes initial condition constraints and makes sub-Planckian hilltop inflation compatible with recent cosmological data.

Contribution

It introduces a curvaton-assisted mechanism that alleviates initial-value tuning and expands viable parameter space for sub-Planckian hilltop inflation.

Findings

Curvaton coupling relaxes initial-value constraints.

Revives quartic hilltop inflation in sub-Planckian regime.

Finds parameter space consistent with recent observations.

Abstract

Following the recent Atacama Cosmology Telescope (ACT) 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.