$2\nu\beta\beta$ Spectrum in Chiral Effective Field Theory

TL;DR

This paper analyzes the $2 uetaeta$ decay spectrum using chiral effective field theory, highlighting the importance of chiral corrections like weak magnetism and pion exchange for accurate interpretation and potential insights into new physics.

Contribution

It introduces next-to-leading-order chiral corrections to the $2 uetaeta$ decay spectrum and explores their implications for new physics searches and connections to neutrinoless double beta decay.

Findings

Chiral corrections significantly affect the $2 uetaeta$ electron spectrum.

Pion-exchange contributions relate to neutrinoless double beta decay matrix elements.

Chiral effective field theory provides a framework for interpreting double beta decay spectra.

Abstract

We investigate two-neutrino double beta decay ($2\nu\beta\beta$) in chiral effective field theory. We find contributions from weak magnetism and double-weak pion-exchange at next-to-leading-order in the chiral power counting. We discuss the impact of the chiral corrections on the electron spectra and find that they should be included in analyses of $2\nu\beta\beta$ decay that aim to uncover new physics signatures in the electron spectrum. We illustrate this point by revisiting the effect of sterile neutrinos and non-standard charged interactions. We also find that the pion-exchange contributions involve nuclear matrix elements that are related to those appearing in neutrinoless double beta decay ($0\nu \beta \beta$). We investigate whether the $0\nu \beta \beta$ nuclear matrix elements can be obtained from detailed measurements of the energy spectrum of the outgoing electrons in $2\nu\beta\beta$ transitions.