Holographic Wilson Lines as Screened Impurities

TL;DR

This paper demonstrates that in a strongly-coupled holographic model, Wilson line impurities are screened by an adjoint scalar, leading to the formation of quasi-bound states detectable through scattering phase shifts and resonances.

Contribution

It provides evidence that the adjoint scalar screens Wilson lines in holography, with quasi-bound states appearing as quasi-normal modes of probe D3-branes, even without a black hole horizon.

Findings

Quasi-bound states form at the Wilson line impurity.

Screening is evidenced by scattering phase shifts and resonances.

Quasi-normal modes indicate the presence of screened impurities.

Abstract

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 $\mathcal{N}=4$ supersymmetric $SU(N)$ Yang-Mills theory on the Coulomb branch, where an adjoint scalar has a non-zero expectation value that breaks $SU(N) \to SU(N-1) \times U(1)$. 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.