# Purushottam Sahu: Neutrinoless double beta decay in a left-right symmetric model with a double seesaw mechanism

**Purushottam Sahu: Neutrinoless double beta decay in a left-right symmetric model with a double seesaw mechanism**

We discuss a left-right (L-R) symmetric model with the double seesaw mechanism at the TeV scale generating Majorana masses for the active left-handed (LH) flavour neutrinosναL and the heavy right-handed (RH) neutrinos NβR, α,β = e,μ,τ, which in turn mediate lepton number violating processes, including neutrinoless double beta decay. The Higgs sector is composed of two Higgs doublets HL, HR and a bi-doublet Φ. The fermion sector has the usual for the L-R symmetric models quarks and leptons, along with three SU(2) singlet fermion SγL. The choice of bare Majorana mass term for these sterile fermions induces large Majorana masses for the heavy RH neutrinos leading to two sets of heavy Majorana particles Nj and Sk, j, k = 1, 2, 3, with masses mNj ≪ mSk . Working with a specific version of the model in which the ναL − NβR and the NβR − SγL Dirac mass terms are diagonal, and assuming that mNj ∼ (1−1000) GeV and max(mSk) ∼ (1−10) TeV, mNj ≪ mSk, we study in detail the new “non-standard” contributions to the 0νββ decay amplitude and half-life arising due to the exchange of virtual Nj and Sk. We find that in both cases of NO and IO light neutrino mass spectra, these contributions are strongly enhanced and are dominant at relatively small values of the lightest neutrino mass m1(3) ∼ (10−4 − 10−2) eV over the light Majorana neutrino exchange contribution. In large part of the parameter space, the predictions of the model for the 0νββ decay generalised effective Majorana mass and half- life are within the sensitivity range of the planned next generation of neutrinoless double beta decay experiments LEGEND-200 (LEGEND-1000), nEXO, KamlAND-Zen-II, CUPID, NEXT-HD.