On Spontaneous Baryogenesis and Transport Phenomena

Abstract: The spontaneous baryogenesis mechanism by Cohen, Kaplan and Nelson is reconsidered taking into account the transport of particles inside the electroweak bubble walls. Using linear response theory, we calculate the modifications on the thermal averages of the charges of the system due to the presence of a space time dependent `charge potential' for a quantum number not orthogonal to baryon number. The local equilibrium configuration is discussed, showing that, as a consequence of non zero densities for conserved charges, the $B+L$ density is driven to non zero values by sphaleronic processes. Solving a rate equation for the baryon number generation, we obtain an expression for the final baryon asymmetry of the Universe containing the relevant parameters of the bubble wall, {\it i.e.} its velocity, its width, and the width of the region in which sphalerons are active. Compared to previous estimates in which transport effects were not taken into account, we find an enhancement of nearly three orders of magnitude in the baryon asymmetry. Finally, the role of QCD sphalerons in cooperation with transport effects is analyzed, showing that the net result depends crucially on the particle species which enter into the charge potential.