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13 pages, 1343 KiB

Open AccessArticle

Neutrinoless Double-Beta Decay Investigations of ⁸²Se Using Three Shell Model Hamiltonians

by Andrei Neacsu and Mihai Horoi

Symmetry 2024, 16(8), 974; https://doi.org/10.3390/sym16080974 - 31 Jul 2024

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Neutrinoless double-beta decay is considered one of the most promising processes that would help clarify some of the symmetry-breaking problems in our understanding of the observable universe. Recent studies of neutrinoless double-beta decay matrix elements have employed statistical approaches based on modified shell model effective Hamiltonians for ⁴⁸Ca (Phys. Rev. C 106, 054302 (2022)) and ¹³⁶Xe (Phys. Rev. C 107, 045501 (2023)). The analyses rely on inducing perturbations in the starting effective Hamiltonians to observe the behavior of a wide range of observables, besides the

0 ν β β

) NME, that are compared with experimental data. Following a Bayesian model averaging approach, the range of probable values for the neutrinoless double-beta decay matrix elements is presented. In this paper, we present a similar study for ⁸²Se, which is described in the same model space as ⁷⁶Ge that is under experimental observation. Due to its faster calculation time compared to ⁷⁶Ge, ⁸²Se can be used as an appropriate substitute in our complex statistical study. Using the calculations performed for the statistical analysis of the neutrinoless double-beta decay matrix elements, we also search for the correlations between the observables that we can compare to experimental data. Full article

(This article belongs to the Special Issue Recent Advances in Double Beta Decay Investigations: In Honor of Prof. Sabin Stoica at His 70th Anniversary)

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12 pages, 1322 KiB

Open AccessArticle

Improved Statistical Analysis for the Neutrinoless Double-Beta Decay Matrix Element of ¹³⁶Xe

by Mihai Horoi

Universe 2024, 10(6), 252; https://doi.org/10.3390/universe10060252 - 4 Jun 2024

Cited by 1 | Viewed by 943

Abstract

Neutrinoless double beta decay nuclear matrix element (

M_{0 ν}

) for ¹³⁶Xe was recently analyzed using a statistical approach (Phys. Rev. C 107, 045501 (2023)). In the analysis, three initial shell model effective Hamiltonians were randomly altered, and their [...] Read more.

Neutrinoless double beta decay nuclear matrix element (

M_{0 ν}

M_{0 ν}

nuclear matrix element (NME) based on a Bayesian Model Averaging approach. In that analysis, a reasonable Gamow-Teller quenching factor of 0.7 was assumed for each starting effective Hamiltonian. Given that the result of the statistical analysis was sensible to this choice, we are here improving that analysis by assuming that the Gamow-Teller quenching factor is also randomly chosen within reasonabe limits for all three starting Hamiltonians. The outcomes are slightly higher expectation values and uncertainties for the

M_{0 ν}

NME. Full article

(This article belongs to the Special Issue Recent Advances in Double Beta Decay Investigations: In Honor of Prof. Sabin Stoica at His 70th Anniversary)

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15 pages, 387 KiB

Open AccessReview

Double Beta Decay: A Shell Model Approach

by Mihai Horoi

Physics 2022, 4(4), 1135-1149; https://doi.org/10.3390/physics4040074 - 26 Sep 2022

Cited by 6 | Viewed by 3110

Abstract

Studies of weak interaction in nuclei are important tools for testing different aspects of the fundamental symmetries of the Standard Model. Neutrinoless double beta decay offers an unique venue of investigating the possibility that neutrinos are Majorana fermions and that the lepton number conservation law is violated. Here, I use a shell model approach to calculate the nuclear matrix elements needed to extract the lepton-number-violating parameters of a few nuclei of experimental interest from the latest experimental lower limits of neutrinoless double beta decay half-lives. The analysis presented here could reveal valuable information regarding the dominant neutrinoless double beta decay mechanism if experimental half-life data become available for different isotopes. A complementary shell model analysis of the two-neutrino double beta decay nuclear matrix elements and half-lives is also presented. Full article

(This article belongs to the Special Issue The Nuclear Shell Model 70 Years after Its Advent: Achievements and Prospects)

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12 pages, 475 KiB

Open AccessArticle

Effects of Atomic-Scale Electron Density Profile and a Fast and Efficient Iteration Algorithm for Matter Effect of Neutrino Oscillation

by Mihai Horoi and Adam Zettel

Universe 2020, 6(1), 16; https://doi.org/10.3390/universe6010016 - 18 Jan 2020

Viewed by 2628

Abstract

In a recent article, we noticed that the electron density in condensed matter exhibits large spikes close to the atomic nuclei. We showed that the peak magnitude of these spikes in the electron densities, 3–4 orders larger than the average electron plasma density in the Sun’s core, have no effect on the neutrino emission and absorption probabilities or on the neutrinoless double beta decay probability. However, it was not clear if the effect of these spikes is equivalent to that of an average constant electron density in matter. We investigated these effects by a direct integration of the coupled Dirac equations describing the propagation of flavor neutrinos into, through, and out of the matter. We proposed a new iteration-based algorithm for computing the neutrino survival/appearance probability in matter, which we found to be at least 20 times faster than some direct integration algorithms under the same accuracy. With this method, we found little evidence that these spikes affect the standard oscillations probabilities. In addition, we show that the new algorithm can explain the equivalence of using average electron densities instead of the spiked electron densities. The new algorithm is further extended to the case of light sterile neutrinos. Full article

(This article belongs to the Special Issue Neutrino Oscillations)

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