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

The time evolution of the baryon asymmetry (knBs) due to the interactions of a superheavy gauge boson (mass MX~10¹⁵ GeV, coupling strength α~1/45) is obtained by numerically integrating the Boltzmann equations. Particle interactions in the very early universe (t10^-35 sec) are assumed to be described by the SU(5) grand unification theory. To a good approximation the results depend upon one parameter, K≡2.9×10¹⁷ α GeVMX. 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 exp(-5.5K). If both C and CP are violated then an initially symmetrical universe evolves a baryon asymmetry which today corresponds to knBs7.8×10^-3ε[1+(16K)1.3], where ε2 is the baryon excess produced when an X-X̄ pair decays. Decays and inverse decays of superheavy bosons are primarily responsible for these results (as Weinberg and Wilczek suggested); however for K1 baryon production falls off much less rapidly than they had expected. A gauge boson of mass 3×{}10¹⁴ GeV could have generated the observed asymmetry knBs10^-9.8±1.6 if ε10^-4.3±1.6. In a companion paper the role of Higgs bosons is considered.