We investigate how hypothetical particles-sterile neutrinos-can be produced in the interior of exploding supernovae via the resonant conversion of nu over bar mu and nu over bar tau. The novelty of... Show moreWe investigate how hypothetical particles-sterile neutrinos-can be produced in the interior of exploding supernovae via the resonant conversion of nu over bar mu and nu over bar tau. The novelty of our treatment lies in the proper account of the resulting lepton number diffusion. We compute the yield of sterile neutrinos and find that even after taking into account backreaction, sterile neutrinos can carry out a sizeable fraction of the total energy of the explosion comparable to that of active neutrinos. The production is, however, sensitive to the temperature in the inner supernovae regions, making robust predictions of challenging. In order to understand whether this production affects supernova evolution and can therefore be constrained, detailed simulations including the effects of sterile neutrinos are needed. Show less
Boyarsky, A.; Ovchynnikov, M.; Sabti, N.; Syvolap, V. 2021
The existence of feebly interacting massive particles (FIMPs) could have significant implications on the effective number of relativistic species N-eff in the early Universe. In this work, we... Show moreThe existence of feebly interacting massive particles (FIMPs) could have significant implications on the effective number of relativistic species N-eff in the early Universe. In this work, we investigate in detail how short-lived FIMPs that can decay into neutrinos affect N-eff and highlight the relevant effects that govern its evolution. We show that even if unstable FIMPs inject most of their energy into neutrinos, they may still decrease N-eff, and identify neutrino spectral distortions as the driving power behind this effect. As a case study, we consider heavy neutral leptons (HNLs) and indicate which regions of their parameter space increase or decrease Neff. Moreover, we derive bounds on the HNL lifetime from the cosmic microwave background and comment on the possible role that HNLs could play in alleviating the Hubble tension. Show less
The extension of the Standard Model with two gauge-singlet Majorana fermions can simultaneously explain two beyond-the-Standard-model phenomena: neutrino masses and oscillations, as well as the... Show moreThe extension of the Standard Model with two gauge-singlet Majorana fermions can simultaneously explain two beyond-the-Standard-model phenomena: neutrino masses and oscillations, as well as the origin of the matter-antimatter asymmetry in the Universe. The parameters of such a model are constrained by the neutrino oscillation data, direct accelerator searches, big bang nucleosynthesis, and requirement of successful baryogenesis. We show that their combination still leaves an allowed region in the parameter space below the kaon mass. This region can be probed by the further searches of NA62, DUNE, or SHiP experiments. Show less
Boiarskyi, O.; Ovchynnikov, M.; Ruchayskiy, O.; Syvolap, V. 2021
We constrain the lifetime of thermally produced heavy neutral leptons (HNLs) from big bang nucleosynthesis. We show that even a small fraction of mesons present in the primeval plasma leads to the... Show moreWe constrain the lifetime of thermally produced heavy neutral leptons (HNLs) from big bang nucleosynthesis. We show that even a small fraction of mesons present in the primeval plasma leads to the overproduction of primordial helium-4. This constrains the lifetime of HNLs to be tau(N) < 0.02 s for masses above the mass of the pion (as compared to 0.1 s reported previously). In combination with accelerator searches, this allows us to put a new lower bound on the HNL masses and define the "bottom line" for HNL searches at the future Intensity Frontier experiments. Show less
