Two-photon exchange at lowQ2

We studied two-photon exchange for elastic electron-proton scattering at low $Q^2$. Compact approximate formulas for the amplitudes were obtained. Numerical calculations were done for $Q^2⩽0.1{\mathrm{GeV}}^2$ with several realistic form factor parametrizations, yielding similar results. They indicate that the corrections to the magnetic form factor can visibly affect the cross-section and proton radii. For low-$Q^2$ electron-neutron scattering two-photon exchange corrections were shown to be negligibly small.