A new mathematical model of quantum fields has revealed a negative coefficient in a place where physics almost always demands a positive one.
April 24, 2026
Original Paper
Weyl Anomaly Coefficients of Holographic Defect CFTs at Weak and Strong Coupling
arXiv · 2604.19881
The Takeaway
Interacting unitary defect conformal field theories can produce a negative type-A Weyl anomaly coefficient. In standard quantum field theory, these coefficients are typically expected to stay positive to ensure the math doesn't break down. Finding a negative value in this specific defect model is a rare theoretical first that challenges our understanding of field stability. This discovery suggests that the rules governing how fields interact with boundaries or defects are more flexible than we assumed. Understanding these edge cases helps physicists build better models of how the fundamental forces behave at extreme boundaries.
From the abstract
We determine the type-A Weyl anomaly coefficient $b$, associated with the intrinsic scalar curvature of the defect, for the class of holographically realised co-dimension two defect CFTs (dCFTs) introduced in arXiv:2506.14505and arXiv:2512.14853. At strong coupling, we employ the dual D5-brane solutions in Euclidean signature, where the defect is supported on an $S^2$ submanifold of the Euclidean $AdS_3\times S^1$ boundary. At weak coupling, we use the classical solutions of the ${\cal N}=4$ SYM