Baryon asymmetry from the decay and scattering of a Majorana fermion pair coupled to quarks

We compute the baryon asymmetry in decay and scattering processes involving the electromagnetically charge-neutral fermion χ that carries the nonzero baryon number and interacts with quarklike fermions U, D via a vector-vector dimension-six effective operator, in the theory we developed in our earlier work. Majorana masses for the χ break the baryon number and split the Dirac fermion χ into a pair of Majorana fermions Xn with an indefinite baryon number. We identify loop amplitudes for Xn decay and scattering processes that are sensitive to the baryon number violation. The phases in the Majorana mass and couplings, in conjunction with the phase from intermediate on-shell states, lead to C and CP violation in these processes. For some representative parameter choices, we numerically compute the decay and scattering baryon asymmetries between the process and its conjugate process and find that the asymmetry generated is very interesting for explaining the baryon asymmetry of the Universe.