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Register a new userMNS Parameters from Neutrino Oscillations, Single Beta Decay and Double Beta Decay
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We examine the constraints on the MNS lepton mixing matrix =66rom the present and future experimental data of the neutrino oscillation, tritium beta decay, and neutrinoless double beta decay for Majorana neutrinos. We show that the small mixing angle solutions for solar neutrino problem are disfavored for small averaged mass ($<m_ u>$) of neutrinoless double beta decay ($leq 0.01$ eV) in the inverse neutrino mass hierarchy scenario. This is the case even in the normal mass hierarchy scenario except for very restrictive value of the averaged neutrino mass ($bar{m_ u}$) of single beta decay. The lower mass bound for $bar{m_ u}$ is given from the present neutrino oscillation data. We obtain some relations between $<m_ u>$ and $bar{m_ u}$. The constraints on the Majorana CP violating phases are also given.
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Neutrino Self-Interactions ($ u$SI) beyond the Standard Model are an attractive possibility to soften cosmological constraints on neutrino properties and also to explain the tension in late and early time measurements of the Hubble expansion rate. The required strength of $ u$SI to explain the $4sigma$ Hubble tension is in terms of a point-like effective four-fermion coupling that can be as high as $10^9, G_F$, where $G_F$ is the Fermi constant. In this work, we show that such strong $ u$SI can cause significant effects in two-neutrino double beta decay, leading to an observable enhancement of decay rates and to spectrum distortions. We analyze self-interactions via an effective operator as well as when mediated by a light scalar. Data from observed two-neutrino double beta decay is used to constrain $ u$SI, which rules out the regime around $10^9, G_F$.
The observation of neutrinoless double beta decay will have important consequences. First it will signal that lepton number is not conserved and the neutrinos are Majorana particles. Second, it represents our best hope for determining the absolute neutrino mass scale at the level of a few tens of meV. To achieve the last goal, however, certain hurdles have to be overcome involving particle, nuclear and experimental physics. Particle physics is important since it provides the mechanisms for neutrinoless double beta decay. In this review we emphasize the light neutrino mass mechanism. Nuclear physics is important for extracting the useful information from the data. One must accurately evaluate the relevant nuclear matrix elements, a formidable task. To this end, we review the recently developed sophisticated nuclear structure approaches, employing different methods and techniques of calculation. We also examine the question of quenching of the axial vector coupling constant, which may have important consequences on the size of the nuclear matrix elements. From an experimental point of view it is challenging, since the life times are extremely long and one has to fight against formidable backgrounds. One needs large isotopically enriched sources and detectors with good energy resolution and very low background.
Recent neutrino experiment results show a preference for the normal neutrino mass ordering. The global efforts to search for neutrinoless double beta decays undergo a broad gap with the approach to the prediction in the three-neutrino framework based on the normal ordering. This research is intended to show that it is possible to find a neutrinoless double beta decay signal even with normal ordered neutrino masses. We propose the existence of a light sterile neutrino as a solution to the higher effective mass of the electron neutrino expected by the current experiments. A few short-baseline oscillation experiments gave rise to a limit on the mass of the sterile neutrino and its mixing with the lightest neutrino. We demonstrate that the results of neutrinoless double beta decays can also narrow down the range of the mass and the mixing angle of the light sterile neutrino.
We examine the prospects of detecting an analogous process of neutrinoless double beta decay at a neutrino factory from a high energy muon storage ring. Limits from LEP experiments, neutrinoless double beta decay as well as from global fits have to be incorporated and severely restrict the results. We investigate what limits on light and heavy effective Majorana neutrino masses can be obtained and compare them with existing ones. Discussed are also contributions from right-handed neutrinos and purely right-handed interactions. Other ``new physics contributions to the same final state might produce large event numbers.
We discuss a mechanism of neutrinoless double beta decay, where neutrinos of different flavours come into play. This is realized by effective flavour-violating scalar interactions. As one consequence, we find that within the normal mass ordering the neutrino effective mass may no longer vanish due to contributions from other flavours. We evaluate the necessary nuclear matrix elements, consider the interference between the standard diagram and the new scalar one, and analyze a UV-complete model that realizes the scalar interaction. Tests of the complete model are possible at colliders and future neutrino experiments. Our scenario represents an alternative mechanism for neutrinoless double beta decay, where nevertheless lepton number violation resides only in Majorana mass terms of light neutrinos.
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