The spectrum of marginally-deformed ${\cal N} = 2$ CFTs with AdS$_4$ S-fold duals of type IIB

A holographic duality was recently established between an ${\cal N} =4$ non-geometric AdS$_4$ solution of type IIB supergravity in the so-called S-fold class, and a three-dimensional conformal field theory (CFT) defined as a limit of ${\cal N} =4$ super-Yang-Mills at an interface. Using gauged supergravity, the ${\cal N} =2$ conformal manifold (CM) of this CFT has been assessed to be two-dimensional. Here, we holographically characterise the large-$N$ operator spectrum of the marginally-deformed CFT. We do this by, firstly, providing the algebraic structure of the complete Kaluza-Klein (KK) spectrum on the associated two-parameter family of AdS$_4$ solutions. And, secondly, by computing the ${\cal N} =2$ supermultiplet dimensions at the first few KK levels on a lattice in the CM, using new exceptional field theory techniques. Our KK analysis also allows us to establish that, at least at large $N$, this ${\cal N} =2$ CM is topologically a non-compact cylindrical Riemann surface bounded on only one side.