The nucleon mass in Nf=2 lattice QCD: finite size effects from chiral perturbation theory

In the framework of relativistic SU(2)f baryon chiral perturbation theory we calculate the volume dependence of the nucleon mass up to and including O(p4). Since the parameters in the resulting finite size formulae are fixed from the pion mass dependence of the large volume nucleon masses and from phenomenology, we obtain a parameter-free prediction of the finite size effects. We present mass data from the recent Nf=2 simulations of the UKQCD and QCDSF Collaborations and compare these data as well as published mass values from the dynamical simulations of the CP-PACS and JLQCD Collaborations with the theoretical expectations. Remarkable agreement between the lattice data and the predictions of chiral perturbation theory in a finite volume is found