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We compute the two photon exchange contributions to elastic scattering ofpolarized electrons from target protons. We use a nonlocal field theoryformalism for this calculation. The formalism maintains gauge invariance andprovides a systematic procedure for making this calculation. The results dependon one unknown parameter \bar b. We compute the two photon exchange correctionto the ratio of electric to magnetic form factors extracted using thepolarization transfer experiments. The correction is found to be small if \barb ~ 1. However for larger values of \bar b>3, the correction can be quitesignificant. The correction to the polarization transfer results goes in theright direction to explain their difference with the ratio measured byRosenbluth separation method. We find that the difference between the twoexperimental results can be explained for a wide range of values of theparameter \bar b. We also find that the corrections due to two photon exchangedepend on the photon longitudinal polarization epsilon. Hence we predict anepsilon dependence of the form factor ratio extracted using the polarizationtransfer technique. Finally we obtain a limit on \bar b by requiring that thenon-linearity in epsilon dependence of the unpolarized reduced cross section iswithin experimental errors.

Two Photon Exchange Contributions to Elastic e + p --> e + p Process in a Nonlocal Field Formalism