1. The problem statement, all variables and given/known data Assume that a high-energy nucleon is emitting a pion, i.e. the process N→N+π. Is the pion real or virtual or both? Motivate your answer with a calculation or a good argument. 2. Relevant equations Virtual particles does not obey energy (and momentum) conservation. The virtual particle never appears in the final state. 3. The attempt at a solution I would say that the answer depends on the excitation enrgy of the nucleon and if the pi meson is reabsorbed. But I would spontaneous say that high - energy nucleon means energy is lower than the mass of delta (1232 MeV, mass of nucleon approx 940MeV, mass pion = 140MeV). Also I would think that the RHS is the final state, so that the pion is a real particle. What do you guys think about that?