Electric Polarizability of Charged Pions from Lattice QCD
Open AccessElectromagnetic polarizabilities are fundamental properties of hadrons which help us understand their structure and quantify the change in internal charge and current distributions induced by external electromagnetic fields. Significant experimental and theoretical effort is dedicated to determine these observables. In this dissertation, I present a study of the charged pion electric polarizability using the background field method in lattice QCD, a calculation directly in terms of quark and gluon dynamics. This approach complements the other theoretical and experimental studies and the methods developed here will help shed light on the open questions in this area. Results are obtained for two pion masses (mπ ≈ 315MeV and mπ ≈ 227MeV) and four dynamical ensembles at each pion mass. Mass shifts due to the applied electric field are extracted by fitting lattice QCD correlators with an effective model that captures the acceleration of the charged pion and the finite-volume effects on the same lattice. The mass shift attributed to the deformation of the pion is then used to compute the electric polarizability. A new fitting procedure is designed to guarantee that the results are manifestly gauge-invariant under different electromagnetic potentials. The results are compared to the predictions from chiral perturbation theory. For smaller volumes we find good agreement, but the results for larger volumes are in tension with chiral perturbation theory predictions.
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