Reproducing the Observed Baryon-to-Photon Ratio Through a Cosmological Bounce

The cosmic microwave background fixes the baryon-to-photon ratio at eta = 6.12e-10, which corresponds to a baryon yield, relative to entropy, of Y_B = 8.69e-11. This paper asks what a baryogenesis mechanism must deliver if the early universe passed through a bounce rather than beginning in an expanding singularity, and finds the target itself unchanged but the bookkeeping altered. Writing the final yield as Y_B = kappa epsilon / g_star, with g_star = 106.75 relativistic degrees of freedom, the CP asymmetry required per decay is epsilon = 9.28e-08 at a representative efficiency kappa = 0.1, 9.28e-09 at unit efficiency, and 9.28e-07 at kappa = 0.01. If the asymmetry were instead produced before the bounce and the bounce generated entropy, the requirement rises in direct proportion to the entropy factor, reaching 9.28e-07 for a modest factor of ten at kappa = 0.1. The conclusion is deliberately plain: a bounce does not lower the price of the observed asymmetry; it moves the deadline by which the price must be paid. All values are computed from stated assumptions, not measured.