On the finite size mass shift formula for stable particles

Luescher's finite size mass shift formula in a periodic finite volume, involving forward scattering amplitudes in the infinite volume, is revisited for the two stable distinguishable particle system. The generalized mass shift formulae for the boson and fermion are derived in the boson-boson and fermion-boson systems, respectively. The nucleon mass shift formula is given in the nucleon-pion system and the relation to the computation within chiral perturbation theory by the QCDSF-UKQCD collaboration is discussed