Holographic duals of 3d S-fold CFTs

Abstract: We construct non-geometric AdS$_4$ solutions of IIB string theory where the fields in overlapping patches are glued by elements of the S-duality group. We obtain them by suitable quotients of compact and non-compact geometric solutions. The quotient procedure suggests CFT duals as quiver theories with links involving the so-called $T[U(N)]$ theory. We test the validity of the non-geometric solutions (and of our proposed holographic duality) by computing the three-sphere partition function $Z$ of the CFTs. A first class of solutions is obtained by an S-duality quotient of Janus-type non-compact solutions and is dual to 3d $\mathcal{N}=4$ SCFTs; for these we manage to compute $Z$ of the dual CFT at finite $N$, and it agrees perfectly with the supergravity result in the large $N$ limit. A second class has five-branes, it is obtained by a M\"obius-like S-quotient of ordinary compact solutions and is dual to 3d $\mathcal{N}=3$ SCFTs. For these, $Z$ agrees with the supergravity result if one chooses the limit carefully so that the effect of the fivebranes does not backreact on the entire geometry. Other limits suggest the existence of IIA duals.