Glueball and Meson Regge Trajectories From the Gauge/String Correspondence

We use the modern perspective on string theory as being holographic dual to gauge theories to revisit one of the early successes of the dual models: being able to describe the Regge trajectories of hadrons. We identify the classical string configurations in supergravity backgrounds (KS and MN) dual to confining gauge theories which correspond to glueballs. Classically, the glueball Regge trajectories are linear, with zero intercept. By performing a semi-classical analysis we find that the trajectories become non-linear, with a positive intercept and positive curvature. When analyzing the string realization of a meson composed of dynamical quarks in large $N_c$ QCD, we find the emergence of a valuable phenomenological model of the meson in terms of two rotating point-like massive particles, connected by a flux tube. The classical Regge trajectories are non-linear due to the massive "endpoints" of the string.