Two-photon exchange correction to $2S$-$2P$ splitting in muonic helium-3   ions
  We calculate the two-photon exchange correction to the Lamb shift in muonic helium-3 ions within the dispersion relations framework. Part of the effort entailed making analytic fits to the electron-$^3$He quasielastic scattering data set, for purposes of doing the dispersion integrals. Our result is that the energy of the 2$S$ state is shifted downwards by two-photon exchange effects by 15.14(49) meV, in good accord with the result obtained from a potential model and effective field theory calculation. 
Carl E. Carlson, Mikhail Gorchtein, Marc Vanderhaeghen
nucl-th hep-ph nucl-ex