Coulomb wave functions of nucleon and Roper on the lattice

By applying a spatially extended sink operator, the nucleon two-point functions are calculated in Coulomb gauge from quenched lattice QCD with overlap fermions. The Bethe-Salpeter wave functions of nucleon and Roper resonance are extracted at different quark masses. The typical size of nucleon is about 0.7 fm, which seems insensitive to the quark masses involved in this work. It is also found that the wave function of Roper has a radial node.