Entropy generation and limits on the anisotropy of the early Universe

An estimate is made of the maximum rate at which the entropy of the primordial plasma increases in the presence of a homogeneous shear in a Bianchi type I cosmology. The minimum entropy increase is also derived using a GUT cross-section. We tentatively conclude that baryon synthesis arguments allow us to set limits on the shear density at nucleosynthesis which are many orders of magnitude smaller than the limits based on nucleosynthesis …