Speaker
Maksym Ovchynnikov
(CERN)
Description
In this talk, I discuss how current and upcoming CMB/BBN data can probe new physics in the MeV-era Universe through observables such as $N_{\rm eff}$, primordial helium, and deuterium. I focus on benchmark scenarios including electromagnetic relic decays and late reheating, neutrinophilic decays, and decays into metastable particles such as $\mu,\pi^{\pm},K$, with examples motivated by ALPs, Majorons, dark photons, and HNLs. I highlight why resolving neutrino spectral distortions is essential: simplified thermal treatments of neutrino evolution can miss qualitative changes in $N_{\rm eff}$ and abundances of light elements. Finally, I ask whether future data will exclude these scenarios - or reveal hints of non-standard MeV cosmology.
Author
Maksym Ovchynnikov
(CERN)