Time delay and time advance in resonance theory

We propose a theory of the resonance–antiresonance scattering process which differs considerably from the classical one (the Breit–Wigner theory), which is commonly used in the phenomenological analysis. Here both resonances and antiresonances are described in terms of poles of the scattering amplitude: the resonances by poles in the first quadrant while the antiresonances by poles in the fourth quadrant of the complex angular momentum plane. The latter poles are produced by non–local potentials, which derive from the Pauli exchange forces acting among the nucleons or the quarks composing the colliding particles.