Baryon Isocurvature Limits on an Asymmetry Generated at a Bounce

If the baryon asymmetry was generated with slightly different efficiency in different places, the universe carries baryon isocurvature perturbations: fluctuations in the baryon-to-photon ratio at fixed total density. Microwave-background data bound such fluctuations tightly. This paper translates an isocurvature fraction bound of beta_iso < 0.038 into an allowed root-mean-square scatter in the asymmetry, finding S_rms below about 4.02e-04 under the stated translation, and tabulates which production scatters pass: a patch-to-patch efficiency scatter of 1e-3 or 1e-4 passes comfortably, while scatters of 0.05 and above do not, with the 1e-2 case recorded as passing = False under the stated limit. A bounce that generates the asymmetry through a spatially varying process, such as inhomogeneous reheating of the bounce surface, must therefore be homogeneous in its efficiency at the sub-percent level. Computed from stated assumptions, not measured.