Multi-particle-state contributions to hadronic correlation functions using chiral perturbation theory

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Current and future lattice QCD simulations with physically light pion masses face new challenges. Multi-particle states with one or more pions cause sizable multi-particle-state contaminations in hadronic correlation functions, leading to large systematic uncertainties in the observables computed by numerical simulations. Chiral perturbation theory, the low-energy effective theory for QCD, can be used to compute analytically these multi-particle-state contaminations. In this project we perform these perturbative calculations for various hadronic structure observables (e.g. the axial, pseudoscalar and electromagnetic form factors) and the form factors relevant for semi- leptonic B to pi decays. Our final results can be used to analytically remove the multi-particle-state contaminations for these observables in the analysis of numerical lattice data, thus eliminating an uncertainty that otherwise would result in a systematic error that is hard to quantify.