ELECTROWEAK BARYOGENESIS USING BARYON NUMBER CARRYING SCALARS

We describe a new mechanism for the generation of the baryon asymmetry of the universe during a first-order electroweak phase transition. Th e mechanism requires the existence of two (or more) baryon number carr ying scalar fields with masses and CP-violating mixing which vary with the Higgs field expectation value. This mechanism can be implemented using squarks in supersymmetric theories or using leptoquarks, Our cen tral observation is that reflection of these scalars from a bubble wal l can yield a significant net baryon number flux into the symmetric ph ase, balanced by a flux of opposite sign into the broken phase, For ge neric parameter choices, scalars with incident energies in a specific, but not narrow, range yield order one reflection asymmetries (between the probability of reflection of the scalers and of their antiparticl es). The interesting energies are those for which there are two propag ating scalars in the symmetric phase but only one in the broken phase. Electroweak sphaleron processes drive the baryon number in the symmet ric phase toward zero, but do not act in the broken phase. Our estimat e of the resulting baryon asymmetry is consistent with cosmological ob servations for a range of mass parameters and CP-violating phases in a supersymmetric implementation, as long as the bubble walls are not to o fast and not too thick. (C) 1998 Elsevier Science B.V.