Purely triplet seesaw and leptogenesis within cosmological bound, dark matter, and vacuum stability

In a novel standard model extension it has been suggested that, even in the absence of right-handed neutrinos and type-I seesaw, purely triplet leptogenesis leading to baryon asymmetry of the universe can be realized by two heavy Higgs triplets which also provide type-II seesaw ansatz for neutrino masses. In this work we discuss this model predictions for hierarchical neutrino masses in concordance with recently determined cosmological bounds and oscillation data including θ23 in the second octant and large Dirac CP phases. We find that for both normal and inverted orderings, the model fits the oscillation data with the sum of the three neutrino masses consistent with current cosmological bounds determined from Planck satellite data. In addition, using this model ansatz for CP-asymmetry and solutions of Boltzmann equations, we also show how successful predictions of baryon asymmetry emerges in the cases of both unflavoured and two-flavoured leptogeneses. With additional Z2 discrete symmetry, a minimal extension of this model is further shown to predict a scalar singlet WIMP dark matter in agreement with direct and indirect observations which also resolves the issue of vacuum instability persisting in the original model. Although the combined constraints due to relic density and direct detection cross section allow this scalar singlet dark matter mass to be mξ=750 GeV, the additional vacuum stability constraint pushes this limiting value to mξ=1.3 TeV which is verifiable by ongoing experiments. We also discuss constraint on the model parameters for the radiative stability of the standard Higgs mass.