γγ decay as a probe of neutrinoless ββ decay nuclear matrix elements

Abstract

We study double gamma (γγ) decay nuclear matrix elements (NMEs) for a wide range of nuclei from titanium to xenon, and explore their relation to neutrinoless double-beta (0νββ) NMEs. To favor the comparison, we focus on double-magnetic dipole transitions in the final ββ nuclei, in particular the γγ decay of the double isobaric analog of the initial ββ state into the ground state. For the decay with equal-energy photons, our large-scale nuclear shell model results show a good linear correlation between the γγ and 0νββ NMEs. Our analysis reveals that the correlation holds for γγ transitions driven by the spin or orbital angular momentum due to the dominance of zero-coupled nucleon pairs, a feature common to 0νββ decay. Our shell-model findings point out the potential of future γγ decay measurements to constrain 0νββ NMEs, which are key to answer fundamental physics questions based on 0νββ experiments.