English

Improved Big Bang Nucleosynthesis constraints on decaying massive relics

High Energy Physics - Phenomenology 2026-05-27 v1 Cosmology and Nongalactic Astrophysics

Abstract

We present updated and improved Big Bang Nucleosynthesis (BBN) constraints on heavy, long-lived beyond the Standard Model (BSM) relics ϕ\phi decaying into pairs of Standard Model particles, covering a comprehensive set of two-body decay channels. We treat the leading effects of these injections in detail, discussing the modification of the neutron-to-proton ratio from hadronic interconversions, as well as hadro- and photodisintegration of the light elements. Our analysis incorporates several important refinements with respect to earlier work. We adopt up-to-date primordial abundance measurements, including the new 4^4He determination and the latest nuclear reaction rates. The hadronic and electromagnetic injection spectra are computed using PYTHIA 8, providing a proper treatment of final-state radiation and hadronisation. We further implement an improved treatment of pnp\leftrightarrow n interconversions, accounting for dynamical equilibrium, kaon-induced processes, and updated rates. Additionally, we make use of a refined hadrodisintegration formalism which allows us to also consider disintegration processes while BBN is still active. Together, these improvements yield updated exclusion contours on lifetime, mass, and abundance of the relic for each decay channel considered. Furthermore, we discuss the irreducible freeze-in contribution from inverse decays.

Keywords

Cite

@article{arxiv.2605.26824,
  title  = {Improved Big Bang Nucleosynthesis constraints on decaying massive relics},
  author = {Sara Bianco and Jonas Frerick and Marco Hufnagel and Kai Schmidt-Hoberg},
  journal= {arXiv preprint arXiv:2605.26824},
  year   = {2026}
}

Comments

52 pages, 23 figures

R2 v1 2026-07-22T07:34:19.492Z