Evolution of cosmological baryon asymmetries. I. The role of gauge bosons

The time evolution of the baryon asymmetry (kn/sub B//s) due to the interactions of a superheavy gauge boson (mass M/sub X/approx.1015 GeV, coupling strength αapprox.1/45) is obtained by numerically integrating the Boltzmann equations. Particle interactions in the very early universe (t< or approx. =10-35 sec) are assumed to be described by the SU(5) grand unification theory. To a good approximation the results depend upon one parameter, Kequivalent2.9 x 1017 α GeV/M/sub X/. If C and CP are not violated in the decays of the superheavy boson no asymmetry develops, and any initial baryon asymmetry is reduced by a factor of-tilde)=exp(-5.5K). If both C and CP are violated then an initially symmetrical universe evolves a baryon asymmetry which today corresponds to kn/sub B//stilde)=7.8 x 10-3epsilon/[1+(16K)/sup 1.3/], where epsilon/2 is the baryon excess produced when an X-X-bar pair decays. Decays and inverse decays of superheavy bosons are primarily responsible for these results (as Weinberg and Wilczek suggested); however for K>>1 baryon production falls off much less rapidly than they had expected. A gauge boson of mass 3 x 1014 GeV could have generated the observed asymmetry kn/sub B//stilde)=10/sup -9.8plus-or-minus1.6/ if epsilontilde)=10/sup -4.3plus-or-minus1.6/. In a companion paper the role of Higgs bosons is considered