Majorana Neutrino Physics and Matter-Antimatter Asymmetry in Type IIA String Theory

We study Majorana neutrino masses and the matter-antimatter asymmetry in Type IIA string theory on a T⁶/(Z₂ × Z₂) orientifold with intersecting D6-branes. Euclidean D2-instantons with Sp(2) Chan-Paton symmetry generate both the seesaw mechanism and the Weinberg operator. The flavour vectors are not computed from a compactification but fixed by matching, so our results are an existence proof. Matching the measured mass-squared differences selects the seesaw-dominated case with normal ordering. Swampland criteria constrain the instanton action and the reheating temperature. A benchmark example reproduces the neutrino parameters, gives ηB ≈ 8.6 × 10⁻¹¹, within an order of magnitude of observation, and predicts mββ =2.594 meV. A parameter scan shows the mass hierarchy is accommodated rather than predicted.