Holographic Wilson Loops, Dielectric Interfaces, and Topological Insulators

TL;DR

This paper uses holography to analyze how interfaces with changing coupling or theta-angle in N=4 SYM affect Wilson loops, revealing electromagnetic-like image charge effects and novel supersymmetric phenomena.

Contribution

It provides the first holographic computation of Wilson loops across interfaces with varying coupling or theta-angle, including supersymmetric cases with unique charge behavior.

Findings

Self-energy and potential include image charge effects similar to electromagnetism.

Supersymmetric interfaces show dramatic differences from electromagnetism, including a case with zero image charge.

Non-supersymmetric interfaces behave similarly to electromagnetic dielectric interfaces.

Abstract

We use holography to study (3+1)-dimensional N=4 supersymmetric SU(Nc) Yang-Mills theory (SYM) in the large-Nc and large coupling limits, with a (2+1)-dimensional interface where the Yang-Mills coupling or theta-angle changes value, or "jumps." We consider interfaces that either break all supersymmetry or that preserve half of the N=4 supersymmetry thanks to certain operators localized to the interface. Specifically, we compute the expectation values of a straight timelike Wilson line and of a rectangular Wilson loop in the fundamental representation of SU(Nc). The former gives us the self-energy of a heavy test charge while the latter gives us the potential between heavy test charges. A jumping coupling or theta-angle acts much like a dielectric interface in electromagnetism: a self-energy or potential includes the effects of image charges. N=4 SYM with a jumping theta-angle may also be interpreted as the low-energy effective description of a fractional topological insulator, as we explain in detail. For non-supersymmetric interfaces, we find that the self-energy and potential are qualitatively similar to those in electromagnetism, despite the differences between N=4 SYM and electromagnetism. For supersymmetric interfaces, we find dramatic differences from electromagnetism which depend sensitively on the coupling of the test charge to the adjoint scalars of N=4 SYM. In particular, we find one special case where a test charge has vanishing image charge.