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

Abstract

We revisit various contributions to neutrinoless double beta decay (0νββ) 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 (λ diagram) and W_L−W_R mixing (η diagram) could give dominant contributions to the 0νββ 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 η contribution by itself could saturate the current experimental limit on the 0νββ 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 λ and η contributions leads to significantly improved 0νββ 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 0νββ, lepton flavor violation and electric dipole moment constraints.