IV.T87 — Fine structure from holonomy corrections

The fine-structure splitting of hydrogen is a higher-order B-sector holonomy correction on T^2 of order alpha_em^4 m_e c^2 ~ 1.8e-4 eV, entirely determined by iota_tau; the n=2 level splits into j=3/2 and j=1/2 components, with the splitting computed from alpha_em ~ (8/15) iota_tau^4 and m_e = m_n/R(iota_tau).