Unitary Dual-Resonance S-matrices

Dual-resonance models realize crossing symmetry, Regge behavior and infinitely many resonances in a compact analytic form but their canonical tree-level realizations fall short of genuine S-matrix unitarity. Here we explicitly construct fully unitary dual-resonance amplitudes distinct from the conventional worldsheet construction. The zero-width resonance towers are promoted into a physical absorptive spectrum that retains their characteristic crossing and Regge organization, while unitarizing the amplitude through a mechanism distinct from standard eikonalization. The resulting S-matrices are also local and analytic, and can contain controllable second-sheet Regge trajectories as well as substantial inelasticity. More broadly, our construction opens up a new route to charting the space of consistent strongly coupled S-matrices.