Weyl anomalies of four dimensional conformal boundaries and defects

Motivated by questions about quantum information and classification of quantum field theories, we consider Conformal Field Theories (CFTs) in spacetime dimension d >= 5 with a conformally-invariant spatial boundary (BCFTs) or 4-dimensional conformal defect (DCFTs). We determine the boundary or defect contribution to the Weyl anomaly using the standard algorithm, which includes imposing Wess-Zumino consistency and fixing finite counterterms. These boundary/defect contributions are built from the intrinsic and extrinsic curvatures, as well as the pullback of the ambient CFT's Weyl tensor. For a co-dimension one boundary or defect (i.e. d = 5), we reproduce the 9 parity-even terms found by Astaneh and Solodukhin, and we discover 3 parity-odd terms. For larger co-dimension, we find 23 parity-even terms and 6 parity-odd terms. The coefficient of each term defines a central charge that characterizes the BCFT or DCFT. We show how several of the parity-even central charges enter physical observables, namely the displacement operator two-point function, the stress-tensor one-point function, and the universal part of the entanglement entropy. We compute several parity-even central charges in tractable examples: monodromy and conical defects of free, massless scalars and Dirac fermions in d >= 6; probe branes in Anti-de Sitter (AdS) space dual to defects in CFTs with d >= 6; and Takayanagi's AdS/BCFT with d = 5. We demonstrate that several of our examples obey the boundary/defect a-theorem, as expected.

Automated summary

Motivated by quantum information and classification of quantum field theories, this study examines Conformal Field Theories (CFTs) in spacetime dimension d >= 5 with conformally-invariant spatial boundaries (BCFTs) or 4-dimensional conformal defects (DCFTs). The boundary or defect contributions to the Weyl anomaly are determined using a standard algorithm, and the central charges characterizing the BCFTs or DCFTs are calculated. In addition, several parity-even and parity-odd terms are discovered, and the impact of the parity-even central charges on physical observables are demonstrated.