Time-like form factors of the nucleon

The electromagnetic form factors are an important tool to explore the structure of the nucleon. The extraction of space-like form factors from electron-proton scattering shows a discrepancy between data of unpolarized Rosenbluth measurements and of polarization experiments. This difference can be explained by means of two-photon exchange corrections. In the time-like region no comparable calculations have been done up to now for the corresponding processes. We investigate the influence of two-photon exchange in the reaction anti pp → e+e- with regard to determination of the time-like form factors and present calculations for future experiments at the PANDA rate at FAIR project.