Search for: All records

Heavy sterile neutrinos can be produced in core-collapse supernovae (CCSNe), which are superb particle generators because of their high densities and temperatures. If the sterile neutrinos are long-lived, these may be produced inside the supernova core and escape the stellar envelope, later decaying into SM particles like photons and neutrinos. In this work, we first improve the original analytical calculation of the γ-ray fluxes from decays. We then revisit the bounds on the sterile neutrino parameter space from the non-observation of γ -rays from SN1987A by the Solar Maximum Mission (SMM) and constraints from the diffuse γ -ray background arising from sterile neutrino decays. We find that the constraints arising from both the SMM data and the diffuse γ -ray background are weaker than those that have previously appeared in the recent literature. Finally, we study the sensitivity of several present and near-future γ -ray telescopes such as e-ASTROGAM and Fermi-LAT, assuming a nearby future galactic CCSN. We show that future observations can probe mixing angles as low as |U_τ/μ4|²∼ 5 × 10^-17. 

Abstract Sterile neutrinos can be produced through mixing with active neutrinos in the hot, dense core of a core-collapse supernova (SN). The standard bounds on the active-sterile mixing (sin²θ) from SN arise from SN1987A energy-loss, requiringE_loss< 10⁵²erg. In this work, we discuss a novel bound on sterile neutrino parameter space arising from the energy deposition through its decays inside the SN envelope. Using the observed underluminous SN IIP population, this energy deposition is constrained to be below ∼ 10⁵⁰erg. Focusing on sterile neutrino mixing only with tau neutrino, for heavy sterile massesm_sin the range 100 – 500 MeV, we find stringent constraints on sin²θ_τreaching two orders of magnitude lower than those from the SN1987A energy loss argument, thereby probing the mixing angles required for Type-I seesaw mechanism. Similar bounds will also be applicable to sterile mixing only with muons (sin²θ_μ). 

Heavy neutral leptons (HNLs) are often among the hypothetical ingredients behind nonzero neutrino masses. If sufficiently light, they can be produced and detected in fixed-target-like experiments. We show that if the HNLs belong to a richer—but rather generic—dark sector, their production mechanism can deviate dramatically from expectations associated with the standard-model weak interactions. In more detail, we postulate that the dark sector contains an axionlike particle (ALP) that naturally decays into HNLs. Since ALPs mix with the pseudoscalar hadrons, the HNL flux might be predominantly associated with the production of neutral mesons (e.g., ${\pi }^0$, $\eta$) as opposed to charge hadrons (e.g., ${\pi }^{\pm }$, $K^{\pm }$). In this case, the physics responsible for HNL production and decay are not directly related and experiments like DUNE might be sensitive to HNLs that are too weakly coupled to the standard model to be produced via weak interactions, as is generically the case of HNLs that play a direct role in the type-I seesaw mechanism. Published by the American Physical Society2024 

Beyond the Standard Model electromagnetic properties of neutrinos may lead to copious production of sterile neutrinos in the hot and dense core of a core-collapse supernova. In this work, we focus on the active-sterile transition magnetic moment portal for heavy sterile neutrinos. Firstly, we revisit the SN1987A cooling bounds for dipole portal using the integrated luminosity method, which yields more reliable results (especially in the trapping regime) compared to the previously explored via emissivity loss, also known as the Raffelt criterion. Secondly, we obtain strong bounds on the dipole coupling strength reaching as low as 10^{-11} /GeV from energy deposition, i.e., constrained from the observation of explosion energies of underluminous Type IIP supernovae. In addition, we find that sterile neutrino production from Primakoff upscattering off of a proton dominates over scattering off of an electron for low sterile neutrino masses.