Defects in 4d SCFTs from supergravity and holographic renormalization

A bstract Type IIB string theory admits Janus solutions connecting AdS 5 vacua. These geometries correspond to interface conformal field theories and are naturally described in five-dimensional supergravity as AdS 4 foliations over an interval. In this work, we introduce a novel type of Janus solution in AdS 5 , featuring AdS 2 × S 2 foliations instead of AdS 4 . We interpret these solutions as the supergravity duals of line defects in four-dimensional SCFTs and we discuss their D-brane engineering. Our primary tool is Romans supergravity in five dimensions, which provides a simple Type IIB truncation over S 5 . Within this framework, under specific conditions, we construct regular solutions interpolating between AdS 5 and AdS 2 × ℝ 3 . These geometries represent one-parameter deformations of AdS 5 vacua and are characterized by a running profile for two-form gauge potentials and a scalar field in the supergravity bulk. Finally, using holographic renormalization, we explicitly compute the on-shell action of the defect and we discuss the one-point functions in the holographic field theory.