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Gravitational waves from supermassive right-handed neutrinos produced at preheating

Shinya Kanemura1,*, Kunio Kaneta2,†, and Dibyendu Nanda1,3,‡

  • 1Department of Physics, The University of Osaka, Toyonaka, Osaka 560-0043, Japan
  • 2Faculty of Education, Niigata University, Niigata 950-2181, Japan
  • 3Department of Physics, School of Basic Sciences and Humanities, SR University, Warangal 506371, India

  • *Contact author: kanemu@het.phys.sci.osaka-u.ac.jp
  • †Contact author: kaneta@ed.niigata-u.ac.jp
  • ‡Contact author: dnanda@het.phys.sci.osaka-u.ac.jp
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Phys. Rev. D 113, 055046 – Published 26 March, 2026

DOI: https://doi.org/10.1103/rr5v-3jvg

Abstract

The postinflationary production of supermassive particles can have profound implications for the thermal history of the Universe and may leave observable imprints in the gravitational wave (GW) background. In scenarios where the inflaton couples predominantly to heavy fields, say right-handed neutrinos (RHNs), nonperturbative mechanisms such as parametric resonance can lead to their efficient production, even when their masses exceed the inflaton mass. Once produced, the RHNs emit gravitons through bremsstrahlung as they decay into the Standard Model (SM) particles via N→ℓ+H, enabled by the unavoidable minimal coupling to gravity, sourcing a stochastic GW background. We study this mechanism within the framework of α-attractor inflationary models, highlighting how the resulting GW spectrum carries indirect imprints of the heavy sector and the postinflationary dynamics. This offers an observational window into otherwise inaccessible supermassive particles and provides a powerful probe of high-scale physics beyond the SM.

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Phys. Rev. D 113, 055046– Published 26 March, 2026
  • Received 16 August 2025
  • Accepted 12 March 2026
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