TeV Scale Left-Right Symmetry and Large Mixing Effects in Neutrinoless Double Beta Decay

We analyze various contributions to neutrinoless double beta decay ($0νββ$) 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 ($λ$-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. 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.

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