Yongchao Zhang, Washington University in St. Louis
Title: Leptogenesis without explicit loops
Abstract: The baryon asymmetry is usually generated from the interference between tree and loop level diagrams in the literature. We propose a novel mechanism for baryon asymmetry involving only tree-level diagrams. In particular, a nonzero $CP$-asymmetry can be generated via at least two sets of interfering tree-level 2->2 or 1->N (N>=3) diagrams. To illustrate it, we consider a simple scotogeneic-type-II seesaw extension of the Standard Model. The imaginary part for the required $CP$-asymmetry comes from the trilinear coupling of inert doublet scalar with the triplet scalar. In this model, neutrino mass is generated by both scotogenic and type-II seesaw contributions, and the real part of the neutral component of the inert-doublet serves as a cold dark matter candidate. The evolutions of dark matter relic density and baryon asymmetry are intimately connected in this scenario.