Gravitational dark matter production from fermionic spectator fields during inflation

Belfiglio A. Luongo O.
July 2025 Springer Science and Business Media Deutschland GmbH

Journal of High Energy Physics
2025 #2025 Issue 7

We investigate the gravitational particle production from vacuum for a minimally coupled fermionic spectator field during a single-field inflationary phase. We observe that metric perturbations arising from the quantum fluctuations of a scalar inflaton field enhance gravitational production, showing that such a perturbative contribution becomes dominant if the field mass is sufficiently smaller than the inflationary Hubble rate. We focus on modes that leave the Hubble horizon during the latest stages of slow-roll and we numerically compute the total number of particles obtained from perturbations, providing a lower bound on the amount of such “geometric” particles for the case of Starobinsky inflation and a quadratic hilltop scenario. Our outcomes are compatible with the net observational cold dark matter abundance as experimentally measured, whose dark matter candidate exhibits mass in the range 10⁵ ≲ m ≲ 10⁷ GeV, excluded by previous non-perturbative calculations.

Cosmological models , de Sitter space , Effective Field Theories , Particle Nature of Dark Matter

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DSFTA, University of Siena, Via Roma 56, Siena, 53100, Italy
School of Science and Technology, University of Camerino, Via Madonna delle Carceri, Camerino, 62032, Italy
SUNY Polytechnic Institute, Utica, 13502, NY, United States
Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Perugia, Perugia, 06123, Italy
INAF - Osservatorio Astronomico di Brera, Milano, Italy
Al-Farabi Kazakh National University, Al-Farabi av. 71, Almaty, 050040, Kazakhstan

DSFTA
School of Science and Technology
SUNY Polytechnic Institute
Istituto Nazionale di Fisica Nucleare (INFN)
INAF - Osservatorio Astronomico di Brera
Al-Farabi Kazakh National University

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