Holographic Wilson lines as screened impurities

In Landau Fermi liquids, screened impurities support quasi-bound states, representing electrons bound to the impurity but making virtual excursions away. Signals of these quasi-bound states are electron-impurity scattering phase shifts and the corresponding resonances in cross sections. We consider large- N , strongly-coupled (3 + 1)-dimensional N $$ \mathcal{N} $$ = 4 supersymmetric SU( N ) Yang-Mills theory on the Coulomb branch, where an adjoint scalar has a non-zero expectation value that breaks SU( N ) → SU( N − 1) × U(1). In the holographic dual we re-visit well-known solutions for a probe D3-brane that describe this theory with a symmetric-representation Wilson line “impurity”. We present evidence that the adjoint scalar screens the Wilson line, by showing that quasi-bound states form at the impurity, producing U(1)-impurity scattering phase shifts and corresponding resonances in cross sections. The quasi-bound states appear holographically as quasi-normal modes of probe D3-brane fields, even in the absence of a black hole horizon, via a mechanism that we argue is generic to screened defects in holography. We also argue that well-known generalisations of these probe D3-brane solutions can describe lattices of screened Wilson/’t Hooft line impurities.