Precision Particle Physics from extreme ASTROphysical transients

Supernovae (SNe) and neutron star mergers (NSMs) host matter in extreme conditions, exhibiting processes, within the Standard Model (SM) and beyond it (BSM), not testable on Earth. The hot, dense cores of these objects are factories of BSM particles, such as axions, sterile neutrinos, and millicharged particles (MCPs). BSM particles emission may alter the duration of the neutrino burst observed from the historical SN 1987A, but the seminal studies are based on outdated SN simulations. BSM particle emission would also have produced a characteristic gamma-ray burst concurrent with the NSM GW 170817, potentially constraining multiple BSM models, including sterile neutrinos and MCPs, for which no investigation exists. Further, self-interactions in the BSM sector, predicted for many dark matter (DM) candidates but neglected in historical studies, can alter the nature of the BSM outflow. This action will provide a unified answer to these shortcomings, reassessing SN bounds on BSM particle emission using updated SN simulations, including the impact of potential self-interactions, and extending the use of NSMs as a probe of BSM particles. Further, the dense neutrino outflows are sizably affected by neutrino self-interactions. Even SM weak interactions trigger collective flavor conversions, whose outcome is only recently being cleared up. Secret neutrino self-interactions, stronger than the weak ones, can alter both the neutrino light curve and flavor conversions. We will consider this impact to potentially draw constraints on secret neutrino interactions.