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

We revisit 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 show 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 with large left-right neutrino mixing. 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.