Neutrinoless double beta decays of hyperons in covariant chiral perturbation theory

TL;DR

This paper investigates neutrinoless double beta decays of hyperons using covariant chiral perturbation theory, revealing that short-range operators dominate the decay amplitude and providing predictions for decay rates far below current experimental limits.

Contribution

It introduces a covariant chiral perturbation theory approach to hyperon $0 uetaeta$ decays, highlighting the dominance of short-range operators and proposing lattice QCD methods to determine key form factors.

Findings

Decay rates are over 20 orders of magnitude below experimental bounds.

Short-range counterterms dominate the decay amplitude.

Differential decay rates are predicted for all accessible hyperon channels.

Abstract

Neutrinoless double beta ($0\nu\beta\beta$) decays of spin-1/2 hyperons are investigated in a covariant baryon chiral perturbation theory framework, extended by a $\Delta L=2$ operator proportional to the Majorana neutrino mass, where $L$ denotes the lepton number. Within the light Majorana neutrino exchange mechanism, the decay amplitudes are found to emerge at the one-loop level, representing the long-range contribution. The extended-on-mass-shell scheme is employed to renormalize the one-loop amplitudes and restore consistent chiral power counting. Consequently, the differential decay rates for all accessible hyperon $0\nu\beta\beta$ channels are predicted and the corresponding branching ratios are more than 20 orders of magnitude smaller than the current experimental upper bounds. Interestingly, it is found that the leading contribution to hyperon $0\nu\beta\beta$ decay is actually from short-range counterterm operators, as required by the renormalization argument. Neutrinoless transition form factors are proposed to determine this leading contribution through future lattice QCD simulations.