Aspects of Integrability in AdS/CFT Duality
  In this dissertation, we discuss how our understanding of the large-N spectrum of AdS/CFT has been deepened by integrability-based approaches. We begin with a comprehensive review of the integrability of the gauge theory spin-chain and that of the string sigma model. In the light of the AdS/CFT duality, they should be just two ways of describing the same underlying integrability, and it is believed that the unified integrability can be characterised by a set of Bethe ansatz equations which is valid for all values of the 't Hooft coupling. By studying the asymptotic spectrum of the AdS/CFT in the infinite spin/R-charge limit, we first identify the corresponding solitonic counterparts in the context of the AdS/CFT, which are the so-called dyonic giant magnons and the SYM magnon boundstates. Then we show that the S-matrix computed directly from the string solitons scattering precisely reproduces the prediction from the conjecture. We further perform an analyticity test by studying the singularities of the conjectured magnon boundstate S-matrix and checking the physicality conditions. These tests give strong positive supports for the integrability of large-N AdS/CFT as well as the specific form of the conjectured Bethe ansatz equations. Concerning the string theory integrability, we also provide a detailed study of certain classical string solutions on AdS_5 x S^5. These are constructed in such a way they correspond to generic soliton solutions of (Complex) sine/sinh-Gordon equations via the so-called Pohlmeyer reduction procedure. Furthermore, we describe them in terms of algebro-geometric data as finite-gap solutions, giving a complete map of the elliptic string solutions. 
Keisuke Okamura