Quark-antiquark composite systems: The Bethe-Salpeter equation in the spectral-integration technique in the case of different quark masses

AbstractThe Bethe-Salpeter equations for quark-antiquark composite systems with different quark masses, such as $$q\bar s(with q = u,d),q\bar Q$$ , and $$s\bar Q$$ (with Q = c, b), are written in terms of spectral integrals. For mesons characterized by the mass M, spin J, and radial quantum number n, the equations are written for the (n, M2) trajectories with fixed J. The mixing between states with different quark spin S and angular momentum L is also discussed.