# ZZ brane The ZZ brane is a boundary state in [[0562 Liouville theory|Liouville CFT]] defined by $|Z Z\rangle=\int_0^{\infty} d P \Psi_{\rm ZZ}(P) \| P\rangle\rangle, \quad \Psi_{\rm Z Z}(P)=\frac{2 \pi i P}{\Gamma(1-2 i b P) \Gamma\left(1+\frac{2 i P}{b}\right)}.$ In the context of string theory, the ZZ brane can be thought of as a [[0156 D-brane|D-brane]] that exists in the target space of the [[0562 Liouville theory|Liouville theory]]. Unlike [[0658 FZZT brane|FZZT branes]], ZZ branes are unstable Liouville branes localized in the strong coupling region of the Liouville direction. ## Refs - original - [[2001#Zamolodchikov, Zamolodchikov]] ## Related topics - [[0658 FZZT brane]] - [[0642 Boundary Liouville CFT]]