Inverse seesaw mechanism, leptogenesis, observable proton decay, andΔR±± in supersymmetric SO(10) with heavy WR

Abstract

We explore the prospects of low-scale leptogenesis in a class of supersymmetric SO(10) models using extra singlet neutrinos (Ti, i=1, 2, 3) and the Higgs representations 126H⊕ ¯¯¯¯¯¯¯126H as well as 16H⊕¯¯¯¯¯16H. A singlet neutrino, which we show can be as light as 105–106 GeV, decays through its small mixings with right-handed (RH) neutrinos creating a lepton asymmetry which is explicitly shown to be flavor dependent. While the doublet vacuum expectation value in ¯¯¯¯¯16H triggers the generation of desired mixings, it also induces a large RH-triplet vacuum expectation value that breaks the left-right intermediate gauge symmetry and gives large right-handed neutrino masses. Manifest unification of gauge couplings and generation of heavy RH neutrino masses are achieved by purely renormalizable interactions. The canonical (Type-I) seesaw contributions to the light neutrino mass matrix cancel out while the Type-II seesaw contribution is negligible. Determining the parameters of the dominant inverse seesaw formula by using the underlying quark-lepton symmetry and neutrino oscillation data, we show how leptogenesis under the gravitino constraint is successfully implemented. New formulas for the decay rate and the asymmetry parameter are derived leading to baryon asymmetry within the observed range without invoking a resonant condition on RH neutrinos. The model is found to work for hierarchical as well as inverted hierarchical light neutrino masses. Testable predictions of the model are RH doubly charged Higgs bosons which may be leptophilic and accessible to the Tevatron, LHC or a linear collider. In a model-independent manner, the Drell-Yan pair production cross section at the Tevatron or LHC is shown to be bounded between 59%–79% of their left-handed counterparts with same mass. In contrast to single-step breaking supersymmetric grand unified theories, which predict a long proton lifetime for the decay p→e+π0, here this lifetime is substantially reduced, bringing it within one order of the current experimental limit.