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We report on a chiral effective field theory calculation of Compton scattering from the proton. Our calculation includes pions, nucleons, and the Delta(1232) as explicit degrees of freedom. It uses the delta expansion, and so implements the hierarchy of scales m_pi < M_Delta-M_N < Lambda_chi. In this expansion the power counting in the vicinity of the Delta peak changes, and resummation of the loop graphs associated with the Delta width is indicated. We have computed the nucleon Compton amplitude in the delta expansion up to N3LO for photon energies of the order of m_pi. This is the first order at which the proton Compton scattering amplitudes receive contributions from contact operators which encode contributions to the spin-independent polarisabilities from states with energies of the order of Lambda_chi. We fit the coefficients of these two operators to the experimental proton Compton data that has been taken in the relevant photon-energy domain, and are in a position to extract new results for the proton polarisabilities alpha and beta.
We report observables for elastic Compton scattering from $^3$He in Chiral Effective Field Theory with an explicit $Delta(1232)$ degree of freedom ($chi$EFT) for energies between 50 and 120 MeV. The $gamma,{}^3$He amplitude is complete at N3LO, $math
We calculate the $N^*$ contributions to the generalized polarizabilities of the proton in virtual Compton scattering. The following nucleon excitations are included: $N^*(1535)$, $N^*(1650)$, $N^*(1520)$, $N^*(1700)$, $Delta(1232)$, $Delta^*(1620)$ a
Compton scattering off the proton in the third resonance region is analyzed for the first time, owing to the full combined analysis of pion- and photo-induced reactions in a coupled-channel effective Lagrangian model with K-matrix approximation. Two
Real and virtual Compton scattering has been and will be an important tool to study the structure of hadronic systems. We summarize the status of real Compton scattering and give an outlook at the new theoretical and experimental developments in the field of virtual Compton scattering.
We analyze virtual Compton scattering off the nucleon at low energies in a covariant, model-independent formalism. We define a set of invariant functions which, once the irregular nucleon pole terms have been subtracted in a gauge-invariant fashion