Left-right symmetry and leading contributions to neutrinoless double beta decay

TL;DR

This paper investigates how mixing between the standard model W boson and a hypothetical heavier W_R boson affects neutrinoless double beta decay rates, highlighting a potentially dominant long-range pion exchange contribution.

Contribution

It demonstrates that LR mixing can dominate the decay rate through long-range pion exchange, a novel insight in minimal left-right symmetric models with type-II dominance.

Findings

LR mixing can significantly enhance decay rates

Long-range pion exchange may dominate over short-range contributions

Positive signals are still possible even if inverted hierarchy is ruled out

Abstract

We study the impact of the mixing (LR mixing) between the standard model $W$ boson and its hypothetical, heavier right-handed parter $W_R$ on the neutrinoless double beta decay ($0\nu\beta\beta$-decay) rate. Our study is done in the minimal left-right symmetric model assuming type-II dominance scenario with charge conjugation as the left-right symmetry. We then show that the $0\nu\beta\beta$-decay rate may be dominated by the contribution proportional to this LR mixing, which at the hadronic level induces the leading-order contribution to the interaction between two pions and two charged leptons. The resulting long-range pion exchange contribution can significantly enhance the decay rate compared to previously considered short-range contributions. Finally, we find that even if future cosmological experiments rule out the inverted hierarchy for neutrino masses, there are still good prospects for a positive signal in the next generation of $0\nu\beta\beta$-decay experiments.