Abstract

Neutrinoless double beta (0νββ) decay searches are currently among the major foci of experimental physics. The observation of such a decay will have important implications in our understanding of the intrinsic nature of neutrinos and shed light on the limitations of the Standard Model. The rate of this process depends on both the unknown neutrino effective mass and the nuclear matrix element (M0ν) associated with the given 0νββ transition. The latter can only be provided by theoretical calculations, hence the need of accurate theoretical predictions of M0ν for the success of the experimental programs. This need drives the theoretical nuclear physics community to provide the most reliable calculations of M0ν. Among the various computational models adopted to solve the many-body nuclear problem, the shell model is widely considered as the basic framework of the microscopic description of the nucleus. Here, we review the most recent and advanced shell-model calculations of M0ν considering the light-neutrino-exchange channel for nuclei of experimental interest. We report the sensitivity of the theoretical calculations with respect to variations in the model spaces and the shell-model nuclear Hamiltonians.

Highlights

  • Neutrinoless double beta (0νββ) decay is a process in which two neutrons inside the nucleus transform into two protons with the emission of two electrons and no neutrinos

  • We focus on the sensitivity of the calculations with respect to variations in the model spaces and the shell-model nuclear Hamiltonians, as well as to the variations in the “short-range correlations” which reveal the role of shell model (SM) correlated wave functions

  • We test different phenomenological Heff s. All these interactions have been derived modifying the matrix elements of a G-matrix so as to reproduce a chosen set of spectroscopic properties of some nuclei belonging to the mass region of interest

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Summary

Introduction

Neutrinoless double beta (0νββ) decay is a process in which two neutrons inside the nucleus transform into two protons with the emission of two electrons and no neutrinos. While transitions in light nuclei do not have a direct experimental interest, these studies provide us with an important benchmark to test other many-body methods that can be used to calculate transition matrix elements for heavy-mass nuclei of experimental interest They allow us to size the importance of the different lepton number violating mechanisms leading to 0νββ decay processes, and to quantify the effect of the various approximations used in the many-body methods for medium to large nuclear systems. Studies along this line have been carried out (e.g., [18,19,20]).

The Nuclear Shell Model
Short-Range Correlations
The 0νββ-Decay Operator for the Light-Neutrino Exchange
The 2νββ-Decay Operator
Shell-Model Results
Results from Phenomenological Heff s
Results from Realistic Heff s
Comparison between SM Calculations
Conclusions
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