In quantum physics, Regge theory (/ˈrɛdʒeɪ/ REJ-ay, Italian: [ˈrɛddʒe]) is the study of the analytic properties of scattering as a function of angular momentum, where the angular momentum is not restricted to be an integer multiple of ħ but is allowed to take any complex value. The nonrelativistic theory was developed by Tullio Regge in 1959.[1]