Light dark sector via thermal decays of Dark Matter: the case of a 17 MeV particle coupled to electrons

TL;DR

This paper explores whether a 17 MeV particle, suggested by recent experimental anomalies, could serve as a mediator between the Standard Model and hidden sectors, potentially illuminating dark matter interactions.

Contribution

It proposes a novel scenario where a 17 MeV boson coupled to electrons mediates interactions between the Standard Model and dark sectors, motivated by recent experimental hints.

Findings

Analyzes the viability of a 17 MeV mediator in dark matter interactions.

Connects experimental anomalies with theoretical models of dark sector mediators.

Suggests new experimental avenues to test the 17 MeV particle hypothesis.

Abstract

Recent experimental observations, most notably those reported by the ATOMKI and Positron Annihilation into Dark Matter Experiment (PADME) collaborations, have hinted anomalies that may indicate the presence of a new resonance with a mass around $17\,\text{MeV}$, potentially interacting with both nucleons and electrons. Since 2020, ATOMKI has observed this resonance in nuclear transitions from excited to ground states in ${}^{8}\mathrm{Be}$, ${}^{4}\mathrm{He}$, and ${}^{12}\mathrm{C}$. More recently, in 2025, PADME, operating at the Laboratori Nazionali di Frascati, has also hinted a similar excess, in this case in the $e^{+}e^{-}$ final-state events originating from positron annihilation on fixed-target atomic electrons of Carbonium. This concordance strengthens the case for a common underlying origin, potentially involving a new boson, conventionally referred to as $X_{17}$. Despite these intriguing developments, the global experimental landscape remains highly dynamic, particularly in light of recent MEG~II constraints, and a definitive confirmation or exclusion of the $X_{17}$ hypothesis is still lacking. Within this evolving and exciting context, this thesis investigates whether a hypothetical $17\,\text{MeV}$ particle, coupled to electrons as suggested by the PADME observations, could function as a mediator between the Standard Model and previously unexplored hidden sectors. Such a mediator could, in principle, offer a novel pathway toward addressing one of the principal outstanding inconsistencies of the Standard Model: the nature and origin of dark matter.