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| Format: | Preprint |
| Published: |
2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2602.17620 |
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Table of Contents:
- 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.