Standard Model Baryogenesis through Four-fermion Operators in Braneworlds

We study a new baryogenesis scenario in a class of low fundamental scale braneworld models, which typically have difficulty with sufficient baryogenesis. The scenario is characterized by its minimal nature: only 4D short distance operators are those of the Standard Model and gravity. The baryon number-violating operator is a dimension-6 proton decay operator suppressed today by the mechanism of quark-lepton separation in the extra dimensions. We assume that this operator may have been unsuppressed in the early Universe due to a time-dependent quark-lepton separation. The source of CP violation is the CKM mixing, in combination with the dimension-6 operator sector. We find that nearly independently of cosmology, sufficient baryogenesis is nearly impossible in such a scenario if the fundamental scale is above 100 TeV, as required by an unsuppressed neutron-antineutron oscillation operator. The only exception producing sufficient baryon asymmetry is a scenario involving out of equilibrium c quarks interacting with equilibrium b quarks.