Naturally Large Cosmological Neutrino Asymmetries in the Minimal Supersymmetric Standard Model

A large neutrino asymmetry could have significant observable consequences for nucleosynthesis and the cosmic microwave background. If the baryon asymmetry originates via the Affleck-Dine mechanism along a $d=4\mathrm{}$ flat direction of the scalar potential in the minimal supersymmetric standard model and if the lepton asymmetry originates via Affleck-Dine leptogenesis along a $d=6\mathrm{}$ direction, corresponding to the lowest dimension directions conserving $R$ parity, then the ratio $n_L/n_B$ is naturally in the range ${10}^8–{10}^9$. As a result, a potentially observable neutrino asymmetry is correlated with a baryon asymmetry of the order of ${10}^{-10\mathrm{}}$.