Boundary & interface CFTs
A boundary or interface carries its own universal data, even when the bulk critical theory is fixed. I study which boundary conditions and interfaces a theory admits, how symmetry constrains them, and how they can be realized on the lattice. Spectra, entanglement, and responses to quantum quenches provide complementary ways to probe this structure and connect microscopic models with boundary and interface CFTs.
Papers
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Exactly solvable non-unitary conformal interfaces in unitary CFTs
Preprint · arXiv:2606.32035 (2026)
We construct exactly solvable lattice interfaces that preserve conformal symmetry while introducing non-unitarity into an otherwise unitary bulk theory. Matching the lattice and CFT descriptions requires independent incoming and outgoing boundary states with a biorthogonal pairing, and yields a non-unitary generalization of Cardy's consistency condition. The effective central charge governing interface entanglement can be complex; in a subclass where it stays real, it can grow without bound.
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Universal entanglement signatures of interface conformal field theories
Physical Review B 109, L041104 (2024)
We study entanglement across lattice interfaces connecting CFTs with different central charges. For two regions meeting at the interface, mutual information and reflected entropy have the same leading logarithmic scaling. In the models studied, the corresponding effective central charge equals the smaller bulk central charge, showing how correlations across the junction encode interface universality.
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Universal time evolution of string order parameter in quantum critical systems with boundary invertible or noninvertible symmetry breaking
Physical Review B 111, 165121 (2025)
String order provides a dynamical probe of symmetries broken by a boundary or interface. We derive universal decay laws after a quantum quench: exponential in time for a global quench and algebraic for a local quench. The analysis applies to both invertible and noninvertible symmetries, and is verified in lattice models. We also connect string order on a subsystem to full counting statistics.
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Boundary criticality of complex conformal field theory: A case study in the non-Hermitian 5-state Potts model
SciPost Physics 19, 164 (2025)
We identify free, fixed, and mixed conformal boundary conditions in the non-Hermitian five-state Potts chain at its complex bulk fixed point. The spectra of open chains organize into conformal towers that reveal the boundary operator content. Kramers–Wannier duality relates different boundary conditions, extending the study of complex CFTs from bulk conformal data to boundary critical phenomena.