Relativistic Gamow Vectors I Derivation from Poles of the S-Matrix

A state vector description for relativistic resonances is derived from the first order pole of the j -th partial S -matrix at the invariant square mass value s R = ( m − i Γ / 2) 2 in the second sheet of the Riemann energy surface. To associate a ket, called Gamow vector, to the pole, we use the generalized eigenvectors of the four-velocity operators in place of the customary momentum eigenkets of Wigner, and we replace the conventional Hilbert space assumptions for the in- and out-scattering states with the new hypothesis that in- and out-states are described by two different Hardy spaces with complementary analyticity properties. The Gamow vectors have the following properties: -They are simultaneous generalized eigenvectors of the four velocity operators with real eigenvalues and of the self-adjoint invariant mass operator M = ( P µ P µ ) 1 / 2 with complex eigenvalue √ s R . - They have a Breit-Wigner distribution in the invariant square mass variable s and lead to an exactly exponential law for the decay rates and probabilities.