High energy sphalerons for baryogenesis at low temperatures

We discuss baryogenesis in scenarios where the Universe is reheated to temperatures <100 GeV by the decay of long-lived massive particles into energetic SM particles. Before its thermalization, the center-of mass energy in collisions between such a particle and a particle from the ambient plasma can be higher than the typical sphaleron mass, even if the temperature of the plasma itself is much lower. Optimistic estimates for the high energy enhancement of the sphaleron cross section suggest that successful baryogenesis is possible for reheating temperatures as low as 0.1-1 GeV. With a simple extension of the SM, sufficient baryon production should be achieved by enhancing the W-boson coupling even if more pessimistic results for the sphaleron rate are correct. In both cases, if the two to many sphaleron reaction is significant enough for the baryogenesis, the same process can be probed in collider and cosmic-ray experiments. Complementing such experimental tests, a significantly improved understanding of the two to many sphaleron rate in the nonperturbative coupling regime is mandatory to determine whether this scenario is viable. Finally, we briefly discuss the possible origin of the required CP violation.

Automated summary

We discuss baryogenesis in scenarios where the Universe is reheated to low temperatures by the decay of long-lived massive particles into energetic SM particles. Optimistic estimates suggest that successful baryogenesis is possible even for low reheating temperatures. The enhancement of the W-boson coupling in an extended SM model can achieve sufficient baryon production.