Electromagnetic Splittings and Light Quark Masses in Lattice QCD

A method for computing electromagnetic properties of hadrons in lattice QCD is described and preliminary numerical results are presented. The electromagnetic field is introduced dynamically, using a noncompact formulation. Employing enhanced electric charges, the dependence of the pseudoscalar meson mass on the (anti)quark charges and masses can be accurately calculated. At $\beta =5.7\mathrm{}$ with Wilson action, the ${\pi }^{+}-{\pi }^0$ splitting is found to be 4.9(3) MeV. Using the measured $K^0-K^{+}$ splitting, we also find $m_u/m_d=0.512\mathrm{}\left(6\right)$. Systematic errors are discussed.