Eur. Phys. J. C (2025) 85: 197
https://doi.org/10.1140/epjc/s10052-025-13921-8

Regular Article - Theoretical Physics

Primordial black holes from the ultraslow-roll phase in the inflaton–curvaton mixed field inflation

¹ Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, 210023, Nanjing, China
² School of Astronomy and Space Science, University of Science and Technology of China, 230026, Hefei, Anhui, China
³ Department of Physics, College of Sciences, Northeastern University, 110819, Shenyang, China

^a linan@mail.neu.edu.cn
^b fenglei@pmo.ac.cn

Received: 15 November 2024
Accepted: 9 February 2025
Published online: 19 February 2025

Abstract

Primordial black holes (PBHs) are a promising candidate for dark matter, as they can form in the very early universe without invoking new particle physics. This work explores PBH formation within a curvaton scenario featuring an ultraslow-roll (USR) phase. An inflaton–curvaton mixed field model is presented, where the inflaton drives early inflation and then transits into the USR phase, amplifying the small-scale curvature perturbation. During inflation, the curvaton generates entropy perturbation, which later converts into curvature perturbation after the curvaton decays in the radiation-dominated era. Using the $\delta N$ formalism, we compute the power spectrum of the total primordial curvature perturbation and analyze the relevant non-Gaussianity. Our results show that adding a curvaton field not only has a significant impact on primordial non-Gaussianity, but also introduces more complex inflationary dynamics, even saving the inflaton potentials that generate too low scalar spectral indices. Our model can produce PBHs with mass around ${10}^{-14}{M}_{\odot }$ that account for all dark matter, while remaining consistent with current observational constraints.