Physics Colloquium of 8 March 2022

"From the Kondo Problem to Wilson Lines —- Defects in Many-Body Systems"
Zohar Komargodski, Simons Center for Geometry and Physics, Stony Brook Univ.

We review the role of defects in many-body systems and in Quantum Field Theory. The Kondo defect has led to the Renormalization-Group and Wilson line defects have been paramount in the classification of low-energy phases of gauge theories. We review some recent progress on the topic of defects in magnets and in gauge theories. We define a notion of zero-temperature impurity entropy and argue that it captures the number of degrees of freedom on the impurity. We demonstrate this idea for magnetic impurities, pinning field impurities, and Wilson lines, making several experimental predictions on the way.

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