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Regge Trajectories Revisited in the Gauge/String Correspondence

We attempt to obtain realistic glueball Regge trajectories from the gauge/string correspondence. To this end we study closed spinning string configurations in two supergravity backgrounds: Klebanov-Strassler (KS) and Maldacena-Nunez (MN) which are dual to confining gauge theories. These backgrounds represent two embeddings of N=1 SYM, in the large rank limit, in string theory. The classical configuration we consider is that of a folded closed string spinning in a supergravity region with vanishing transverse radius (τ= 0) which is dual to the IR of the gauge theory. Classically, a spinning string yields a linear Regge trajectory with zero intercept. By performing a semi-classical analysis we find that quantum effects alter both the linearity of the trajectory and the vanishing classical intercept: J:=α(t)= α_0 + α' t +β\sqrt{t}. Two features of our Regge trajectories are compatible with the experimental Pomeron trajectory: positive intercept and positive curvature. The fact that both KS and MN string backgrounds give the same functional expression of the Regge trajectories suggests that in fact we are observing string states dual to N=1 SYM.