Lattice calculation of short-range contributions to neutrinoless double-beta decay π⁻ → π ⁺ee at physical pion mass

Abstract

Neutrinoless double-beta (0νββ) decays provide an excellent probe for determining whether neutrinos are Dirac or Majorana fermions. The short-range matrix elements associated with theπ− → π+ee process contribute at leading order in the 0νββ decay channel nn → pp ee through pion exchange between nucleons. However, current lattice calculations show notable discrepancies in predicting these short-range contributions. To address this issue, we perform a lattice QCD calculation of the π− → π+ee matrix elements using domain wall fermion ensembles at the physical pion mass generated by the RBC/UKQCD Collaboration. To mitigate contamination from around-the-world effects, we develop a new method to reconstruct and subtract them directly from lattice data. We then perform a nonperturbative renormalization using the RI/SMOM approach in (γµ, γµ) and (/q, /q) schemes. Compared with previous studies, this work reduces the uncertainties in the matrix elements and provides an independent cross-check that helps to reconcile the discrepancies among previous lattice calculations.

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Identifiers

ORCID for Jonathan M. Flynn: orcid.org/0000-0002-6280-1677

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