Sara Bianco | Searcharxiv

arXiv2026

Improved Big Bang Nucleosynthesis constraints on decaying massive relics

We present updated and improved Big Bang Nucleosynthesis (BBN) constraints on heavy, long-lived beyond the Standard Model (BSM) relics $ϕ$ 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 $^4$He 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 $p\leftrightarrow n$ 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.

hep-ph↗

arXiv2025

Photo- and Hadrodisintegration constraints on massive relics decaying into neutrinos

We perform a detailed study of the cosmological constraints on the decay of a relic particle $ϕ$ into neutrinos, $ϕ\rightarrow ν\barν$, in particular those arising from the observed light-element abundances in the early Universe. We focus on the late-time disintegration of the light elements previously synthesised during BBN. Several processes are relevant, including final-state radiation associated with the decay, as well as subsequent interactions of the injected neutrinos with the thermal background neutrinos or between themselves. All processes generically contribute to the production of electromagnetic and often also hadronic material and may therefore induce late-time photodisintegration and hadrodisintegration reactions, i.e.~the destruction of light elements that have previously been formed during BBN. Here, we examine this scenario with a Monte-Carlo inspired probabilistic approach rather than Boltzmann techniques, taking into account all of these different reactions as well as their interplay. We find the resulting constraints to be very significant, covering a broad range of previously unexplored masses and lifetimes of the relic source particle.

hep-ph↗