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.

• Received 10 September 2014

DOI:https://doi.org/10.1103/PhysRevD.91.113004