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Register a new userCoherent Active-Sterile Neutrino Flavor Transformation in the Early Universe
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We solve the problem of coherent Mikheyev-Smirnov-Wolfenstein (MSW) resonant active-to-sterile neutrino flavor conversion driven by an initial lepton number in the early universe. We find incomplete destruction of lepton number in this process and a sterile neutrino energy distribution with a distinctive cusp and high energy tail. These features imply alteration of the non-zero lepton number primordial nucleosynthesis paradigm when there exist sterile neutrinos with rest masses ~ 1 eV. This could result in better light element probes of (constraints on) these particles.
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Observations of radio pulsars have revealed that they have large velocities which may be greater than 1000 km/s. In this work, the efficacy of an active-sterile neutrino transformation mechanism to provide these large pulsar kicks is investigated. A phase-space based approach is adopted to follow the the transformation of active neutrinos to sterile neutrinos through an MSW-like resonance in the protoneutron star to refine an estimate to the magnitude of the pulsar kick that can be generated in such an event. The result is that this mechanism can create the large pulsar kicks that are observed while not overcooling the star.
We examine medium-enhanced, neutrino scattering-induced decoherent production of dark matter candidate sterile neutrinos in the early universe. In cases with a significant net lepton number we find two resonances, where the effective in-medium mixing angles are large. We calculate the lepton number depletion-driven evolution of these resonances. We describe the dependence of this evolution on lepton numbers, sterile neutrino rest mass, and the active-sterile vacuum mixing angle. We find that this resonance evolution can result in relic sterile neutrino energy spectra with a generic form which is sharply peaked in energy. We compare our complete quantum kinetic equation treatment with the widely-used quantum Zeno ansatz.
Flavor-universal neutrino self-interaction has been shown to ease the tension between the values of the Hubble constant measured from early and late Universe data. We introduce a self-interaction structure that is flavor-specific in the three active neutrino framework. This is motivated by the stringent constraints on new secret interactions among electron and muon neutrinos from several laboratory experiments. Our study indicates the presence of a strongly interaction mode which implies a late-decoupling of the neutrinos just prior to matter radiation equality. Using the degeneracy of the coupling strength with other cosmological parameters, we explain the origin of this new mode as a result of better fit to certain features in the CMB data. We find that if only one or two of the three active neutrino flavors are interacting, then the statistical significance of the strongly-interacting neutrino mode increases substantially relative to the flavor-universal scenario. However, the central value of the coupling strength for this interaction mode does not change by any appreciable amount in the flavor-specific cases. We also briefly analyze a scenario with more than three neutrino species of which only one is self-interacting. In none of the cases, we find a large enough Hubble constant that could resolve the so-called Hubble tension.
Light sterile neutrinos have been introduced as an explanation for a number of oscillation signals at $Delta m^2 sim 1$ eV$^2$. Neutrino oscillations at relatively short baselines provide a probe of these possible new states. This paper describes an accelerator-based experiment using neutral current coherent neutrino-nucleus scattering to strictly search for active-to-sterile neutrino oscillations. This experiment could, thus, definitively establish the existence of sterile neutrinos and provide constraints on their mixing parameters. A cyclotron-based proton beam can be directed to multiple targets, producing a low energy pion and muon decay-at-rest neutrino source with variable distance to a single detector. Two types of detectors are considered: a germanium-based detector inspired by the CDMS design and a liquid argon detector inspired by the proposed CLEAR experiment.
Cosmic inflation is commonly assumed to be driven by quantum fields. Quantum mechanics predicts phenomena such as quantum fluctuations and tunneling of the field. Here we show an example of a quantum interference effect which goes beyond the semi-classical treatment and which may be of relevance in the early universe. We study the quantum coherent dynamics for a tilted, periodic potential, which results in genuine quantum oscillations of the inflaton field, analogous to Bloch oscillations in condensed matter and atomic systems. Our results show that quantum interference phenomena may be of relevance in cosmology.
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