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We propose Bethe equations for the diagonalization of the Hamiltonian of quantum strings on AdS 5 ×S 5 at large string tension and restricted to certain large charge states from a closed su(2) subsector. The ansatz differs from the recently proposed all-loop gauge theory asymptotic Bethe ansatz by additional factorized scattering terms for the local excitations. We also show that our ansatz quantitatively reproduces everything that is currently known about the string spectrum of these states. Firstly, by construction, we recover the integral Bethe equations describing semiclassical spinning strings. Secondly, we explain how to derive the 1/J energy corrections of M-impurity BMN states, provide explicit, general formulae for both distinct and confluent mode numbers, and compare to asymptotic gauge theory. In the special cases M = 2, 3 we reproduce the results of direct quantization of Callan et al. Lastly, at large string tension and relatively small charge we recover the famous 2 4 √ n 2 λ asymptotics of massive string modes at level n. Remarkably, this behavior is entirely determined by the novel scattering terms. This is qualitatively consistent with the conjecture that these terms occur due to wrapping effects in gauge theory. Our finding does not in itself cure the disagreements between gauge and string theory, but leads us to speculate about the structure of an interpolating Bethe ansatz for the AdS/CFT system at finite coupling and charge. † Also at Steklov Mathematical Institute, Moscow.

Recently Lunin and Maldacena used an SL(3, R) transformation of the AdS 5 ×S 5 background to generate a supergravity solution dual to a so-called β-deformation of N = 4 super Yang-Mills theory. We use a T-duality-shift-T-duality (TsT) transformation to obtain the β-deformed background for real β ≡ γ, and show that solutions of string theory equations of motion in this background are in one-to-one correspondence with those in AdS 5 × S 5 with twisted boundary conditions imposed on the U (1) isometry fields. We then apply the TsT transformation to derive a local and periodic Lax pair for the bosonic part of string theory in the γ-deformed background. We also perform a chain of three consecutive TsT transformations to generate a three-parameter deformation of AdS 5 × S 5 . The three-parameter background is dual to a nonsupersymmetric marginal deformation of N = 4 SYM. Finally, we combine the TsT transformations with SL(2, R) ones to obtain a 6 + 2 parameter deformation of AdS 5 × S 5 .

We review the recent advances towards finding the spectrum of the AdS 5 × S 5 superstring. We thoroughly explain the theoretical techniques which should be useful for the ultimate solution of the spectral problem. In certain cases our exposition is original and cannot be found in the existing literature. The present Part I deals with foundations of classical string theory in AdS 5 × S 5 , light-cone perturbative quantization and derivation of the exact light-cone world-sheet scattering matrix. *