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Models of spontaneous wave function collapse have been postulated to address the measurement problem in quantum mechanics. Their primary function is to convert coherent quantum superpositions into incoherent ones, with the result that macroscopic objects cannot be placed into widely separated superpositions for observably prolonged times. Many of these processes will also lead to loss of coherence in neutrino oscillations, producing observable signatures in the flavor profile of neutrinos at long travel distances. The majority of studies of neutrino oscillation coherence to date have focused on variants of the continuous state localization model, whereby an effective decoherence strength parameter is used to model the rate of coherence loss with an assumed energy dependence. Another class of collapse models that have been proposed posit connections to the configuration of gravitational field accompanying the mass distribution associated with each wave function that is in the superposition. A particularly interesting and prescriptive model is Penrose’s description of gravitational collapse which proposes a decoherence time τ determined through Egτ∼ℏ, where Eg is a calculable function of the Newtonian gravitational potential. Here we explore application of the Penrose collapse model to neutrino oscillations, reinterpreting previous experimental limits on neutrino decoherence in terms of this model. We identify effects associated with both spatial collapse and momentum diffusion, finding that the latter is ruled out in data from the IceCube South Pole Neutrino Observatory so long as the neutrino wave packet width at production is σν,x≤2×10−12 m. Published by the American Physical Society 2024
Models of spontaneous wave function collapse have been postulated to address the measurement problem in quantum mechanics. Their primary function is to convert coherent quantum superpositions into incoherent ones, with the result that macroscopic objects cannot be placed into widely separated superpositions for observably prolonged times. Many of these processes will also lead to loss of coherence in neutrino oscillations, producing observable signatures in the flavor profile of neutrinos at long travel distances. The majority of studies of neutrino oscillation coherence to date have focused on variants of the continuous state localization model, whereby an effective decoherence strength parameter is used to model the rate of coherence loss with an assumed energy dependence. Another class of collapse models that have been proposed posit connections to the configuration of gravitational field accompanying the mass distribution associated with each wave function that is in the superposition. A particularly interesting and prescriptive model is Penrose’s description of gravitational collapse which proposes a decoherence time τ determined through Egτ∼ℏ, where Eg is a calculable function of the Newtonian gravitational potential. Here we explore application of the Penrose collapse model to neutrino oscillations, reinterpreting previous experimental limits on neutrino decoherence in terms of this model. We identify effects associated with both spatial collapse and momentum diffusion, finding that the latter is ruled out in data from the IceCube South Pole Neutrino Observatory so long as the neutrino wave packet width at production is σν,x≤2×10−12 m. Published by the American Physical Society 2024
Experimental and theoretical studies of β electrons (electrons emitted in β−-decay transitions) and their β-electron spectra have recently experienced a rapid expansion. These β spectral shapes have been used to study total β spectra of fission-product nuclei in the quest for explanation of the reactor-flux anomalies, and individual β transitions in search for β spectral shapes sensitive to the effective value of the weak axial coupling gA. In the former case the TAGS (total absorption gamma-ray spectroscopy) can be efficiently used to measure the total β spectral shapes and in the latter case dedicated measurements of the involved forbidden nonunique β transitions have been deployed. The fourth-forbidden nonunique decay transitions 113Cd(1/2g.s.+)→113In(9/2g.s.+) and 115In(9/2g.s.+)→115Sn(1/2g.s.+) represent theoretically and experimentally much-studied cases where the total β spectra consist of these single transitions. In these particular cases the TAGS method could be used to assess the effective value of gA. In the present work we have identified five more interesting cases where a total β spectrum consists of a single transition. These spectra correspond to second-forbidden nonunique transitions and are gA and/or sNME dependent, where sNME denotes the so-called small relativistic vector nuclear matrix element. These studies have been performed using the nuclear shell model with well established effective Hamiltonians. With this we target to β transitions that would potentially be of high interest for the TAGS and present and future dedicated β-spectrum experiments.
This review provides a succinct overview of the basic aspects of neutrino physics. The topics covered include neutrinos in the standard model and the three-neutrino mixing scheme; the current status of neutrino oscillation measurements and what remains to be determined; the seesaw mechanisms for neutrino mass generation and the associated phenomenology, including the leptogenesis mechanism to explain the observed matter–antimatter asymmetry of the Universe; and models for the origin of the pattern of neutrino mixing and lepton masses based on discrete flavour symmetries and modular invariance.
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