Sterile Neutrinos in Colliders and the Early Universe
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I present recent work on the type-I seesaw model, which couples the standard model (SM) to sterile neutrinos that can generate finite masses for the light SM neutrinos and help explain the baryon asymmetry in the eary universe via the mehanism of leptogenesis. We have shown that relativistic and spectator effects associated with the early universe plasma can result in a sign-flip and strong relative enhancement of the final
asymmetry in high-scale leptogenesis scenarios with a vanishing initial abundance of sterile neutrinos.
Sterile neutrinos with sub-TeV masses may be detectable via lepton number violating (LNV) decays at colliders. However, such decays may be suppressed due to a protective approximate pseudo-Dirac symmetry that is necessary if large sterile neutrino production crosssections are to be consistent with `t Hooft natural SM neutrino masses. We have shown that the part of parameter space with `t Hooft natural SM neutrino masses can be split into three regions where pseudo-Dirac symmetry a) does not suppress LNV decays, b) does suppress LNV decays, c) may or may not suppress LNV decays. Region a) covers much of the available parameterspace with sterile neutirno masses .
