Testable leptogenesis and $0νββ$ decay in extended seesaw model

Abstract: We investigate the possibility of observable neutrinoless double beta decay $( 0 \nu \beta\beta)$ and viable leptogenesis within a low-scale extended inverse seesaw mechanism with additional sterile neutrinos. General effective field theory (EFT) considerations suggest that if there are experimentally observable signatures in $0 \nu \beta \beta$-decay and a lepton asymmetry generated by heavy right-handed neutrino decays, thermal leptogenesis is likely to be unviable. However, in this work, we show that in the context of low-scale leptogenesis, one can obtain the observed baryon asymmetry of the universe and observable signatures of $0 \nu \beta \beta$ decay in the presence of additional sterile neutrinos. In this framework, the light neutrino masses are suppressed by the extended seesaw parameter, $\mu$, thereby allowing for $\mathcal{O}(10\, \mathrm{TeV})$ right-handed (RH) neutrinos, while avoiding small Yukawa couplings as in other neutrino mass models and near degeneracies in the RH neutrino spectrum as required by the low-scale leptogenesis paradigm. Contributions to the $0 \nu \beta \beta$-decay rate from additional sterile neutrinos can be appreciable, while the corresponding contributions to the early universe lepton asymmetry washout rate are suppressed by other parameters not entering the $0 \nu \beta \beta$-decay amplitudes. We show that for keV-MeV scale, sterile neutrinos future ton-scale $0\nu\beta\beta$-decay experiments offer potential signals while maintaining viable leptogenesis.