Monodromy Defects in Free Field Theories

Authors: Lorenzo Bianchi, Adam Chalabi, Vladimír Procházka, Brandon Robinson, and Jacopo Sisti Preprint number: UUITP- 16/21 Abstract: We study co-dimension two monodromy defects in theories of conformally coupled scalars and free Dirac fermions in arbitrary d dimensions. We characterise this family of conformal defects by computing the one-point functions of the stress-tensor and conserved current for Abelian flavour symmetries as well as two-point functions of the displacement operator. In the case of d = 4, the normalisation of these correlation functions are related to defect Weyl anomaly coefficients, and thus provide crucial information about the defect conformal field theory. We provide explicit checks on the values of the defect central charges by calculating the universal part of the defect contribution to entanglement entropy. Moreover, we leverage the non-supersymmetric free field results to compute a novel defect Weyl anomaly coefficient in a d = 4 theory of free N = 2 hypermultiplets. In carefully studying the defect operator product expansion, we identify notable relevant operators in the defect theories and use them to study the behaviour of the defect under renormalisation group flow.