Nuclear Physics & RIKEN Theory Seminar

The traditional description of high-energy small-angle scattering in QCD has two components --- a soft Pomeron Regge pole for the tensor glueball, and a hard BFKL Pomeron in leading order at weak coupling. On the basis of gauge/string duality, we present a coherent treatment of the Pomeron. In large-$N$ QCD-like theories, we use curved-space string-theory to describe simultaneously both the BFKL regime and the classic Regge regime. The problem reduces to finding the spectrum of a single $j$-plane Schr\"odinger operator. For ultraviolet-conformal theories, the spectrum exhibits a set of Regge trajectories at positive $t$, and a leading $j$-plane cut for negative $t$, the cross-over point being model-dependent. For theories with logarithmically-running couplings, one instead finds a discrete spectrum of poles at all $t$, where the Regge trajectories at positive
$t$ continuously become a set of slowly-varying and closely-spaced poles at negative $t$. Our results agree with expectations for the BFKL Pomeron at negative $t$, and with the expected glueball spectrum at positive $t$, but provide a framework in which they are unified. Effects beyond the single Pomeron exchange are briefly discussed.