Effective double-beta-decay operator for 76Ge and 82Se

TL;DR

This paper develops an improved shell-model operator for neutrinoless double-beta decay in 76Ge and 82Se using many-body perturbation theory, leading to a significant increase in predicted nuclear matrix elements.

Contribution

It introduces a comprehensive method to construct effective decay operators that include higher-order diagrams, enhancing the accuracy of decay rate predictions.

Findings

Effective operator increases nuclear matrix elements by 20% for 76Ge.

Effective operator increases nuclear matrix elements by 30% for 82Se.

Method accounts for physics outside the shell-model space.

Abstract

We use diagrammatic many-body perturbation theory in combination with low-momentum interactions derived from chiral effective field theory to construct effective shell-model transition operators for the neutrinoless double-beta decay of 76Ge and 82Se. We include all unfolded diagrams to first- and second-order in the interaction and all singly folded diagrams that can be constructed from them. The resulting effective operator, which accounts for physics outside the shell-model space, increases the nuclear matrix element by about 20% in 76Ge and 30% in 82Se.