Hyperfine splitting in ordinary and muonic hydrogen

We provide an accurate evaluation of the two-photon exchange correction to the hyperfine splitting of S energy levels in muonic hydrogen exploiting the corresponding measurements in electronic hydrogen. The proton structure uncertainty in the calculation of $\alpha^5$ contribution is sizably reduced.Comment: 5 pages, 4 figures, update in radiative corrections, the resulting HFS is provided, version published in Eur. Phys. J. A 54: 3 (2018

Dispersion relation formalism for the two-photon exchange correction to elastic muon-proton scattering: elastic intermediate state

We evaluate the two-photon exchange correction to the unpolarized cross section in the elastic muon-proton scattering within dispersion relations. One of the six independent invariant amplitudes requires a subtraction. We fix the subtraction function to the model estimate of the full two-photon exchange at one of three MUSE beam energies and make a prediction for the two other energies. Additionally, we present single and double polarization observables accounting for the lepton mass.Comment: 16 pages, 9 figures, version published in Eur. Phys. J. C, 78 6 (2018) 51

Two-photon exchange correction to the Lamb shift and hyperfine splitting of S levels

We evaluate the two-photon exchange corrections to the Lamb shift and hyperfine splitting of S states in electronic hydrogen relying on modern experimental data and present the two-photon exchange on a neutron inside the electronic and muonic atoms. These results are relevant for the precise extraction of the isotope shift as well as in the analysis of the ground state hyperfine splitting in usual and muonic hydrogen.Comment: 5 pages, 1 figure, version published in Eur. Phys. J. A 55; 64 (2019