TeV-scale left-right symmetry and large mixing effects in neutrinoless double beta decay

Abstract

We analyze various contributions to neutrinoless double beta decay ($0\nu\beta\beta$) in a TeV-scale Left-Right Symmetric Model (LRSM) for type-I seesaw dominance. We find that the momentum-dependent effects due to $W_L-W_R$ exchange ($\lambda$-diagram) and $W_L-W_R$ mixing ($\eta$-diagram) could give dominant contributions to the $0\nu\beta\beta$ amplitude in a wide range of the LRSM parameter space. In particular, for a relatively large $W_L-W_R$ mixing, the $\eta$-contribution by itself could saturate the current experimental limit on the $0\nu\beta\beta$ half-life, thereby providing stringent constraints on the relevant LRSM parameters, complementary to the indirect constraints derived from lepton flavor violating observables. In a simplified scenario parametrized by a single light-heavy neutrino mixing, the inclusion of the $\lambda$ and $\eta$ contributions leads to significantly improved $0\nu\beta\beta$ constraints on the light-heavy neutrino mixing as well as on the $W_L-W_R$ mixing parameters. We also present a concrete TeV-scale LRSM setup, where the mixing effects are manifestly enhanced, and discuss the interplay between $0\nu\beta\beta$, lepton flavor violation and electric dipole moment constraints.