Washout Survival of a Baryon Asymmetry Across the Hot Phase of a Bounce

An asymmetry produced before or during the hot phase of a bouncing cosmology is partially erased by the same interactions that created it, a process called washout. This paper computes the surviving fraction of an initial baryon yield as a function of a washout strength K and of the duration of the hot phase, which a bounce can lengthen. For weak washout, K = 0.1, the surviving fraction is 0.976; at K = 1 it is 0.785; at K = 10 it falls to 8.84e-02 for a standard hot phase and to 7.81e-03 when the bounce triples that phase; at K = 100 essentially nothing survives, with a fraction of 2.91e-11. The integrated washout at K = 10 is W = 2.43 e-foldings of depletion. The practical result is a survival boundary: production mechanisms operating in the strong-washout regime cannot rely on an asymmetry made before the bounce, whatever its initial size within reasonable bounds. Computed from stated assumptions, not measured.