Bootstrapping boundaries and branes

• Published in: The journal of high energy physics 2023-02, Vol.2023 (2), p.19-70, Article 19
• Main Authors: Collier, Scott, Mazáč, Dalimil, Wang, Yifan
• Format: Article
• Language: English
• Subjects: Annuli; Boundary conditions; Branes; Classical and Quantum Gravitation; Conformal Field Models in String Theory; D-Branes; Elementary Particles; Entropy; Field Theories in Lower Dimensions; High energy physics; Partitions (mathematics); Physics; Physics and Astronomy; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Regular Article - Theoretical Physics; Relativity Theory; Scale and Conformal Symmetries; String Theory
• ISSN: 1029-8479; 1029-8479
• DOI: 10.1007/JHEP02(2023)019

A bstract The study of conformal boundary conditions for two-dimensional conformal field theories (CFTs) has a long history, ranging from the description of impurities in one-dimensional quantum chains to the formulation of D-branes in string theory. Nevertheless, the landscape of conformal boundaries is largely unknown, including in rational CFTs, where the local operator data is completely determined. We initiate a systematic bootstrap study of conformal boundaries in 2d CFTs by investigating the bootstrap equation that arises from the open-closed consistency condition of the annulus partition function with identical boundaries. We find that this deceivingly simple bootstrap equation, when combined with unitarity, leads to surprisingly strong constraints on admissible boundary states. In particular, we derive universal bounds on the tension (boundary entropy) of stable boundary conditions, which provide a rigorous diagnostic for potential D-brane decays. We also find unique solutions to the bootstrap problem of stable branes in a number of rational CFTs. Along the way, we observe a curious connection between the annulus bootstrap and the sphere packing problem, which is a natural extension of previous work on the modular bootstrap. We also derive bounds on the boundary entropy at large central charge. These potentially have implications for end-of-the-world branes in pure gravity on AdS 3 .