Hadronic Lorentz Violation in Chiral Perturbation Theory

The leading-order Lorentz-violating hadronic Lagrange densities are constructed using chiral perturbation theory. This is done for both pions and nucleons starting from a two-flavor quark-level Lagrangian that consists of dimension-four Lorentzviolation operators. The effective Lagrangians are first constructed in the absence of external fields. The formalism is then extended to include interactions with external fields. The presence of Lorentz violation modifies the transformation behavior of external fields under the chiral group SU(2)L × SU(2)R. This in turn leads to modified pion and nucleon covariant derivatives. By expanding parts of both mesonic and baryonic Lagragians in terms of physical pion and nucleon fields, new approximate bounds on the effective pion Lorentz-violation coefficients are placed using experimental observations from the proton and neutron sectors. The resulting constraints on four pion parameters are at the 10-23 level