Boundary transitions of the O(n) model on a dynamical lattice

We study the anisotropic boundary conditions for the dilute O(n) loop model with the methods of 2D quantum gravity. We solve the problem exactly on a dynamical lattice using the correspondence with a large $N$ matrix model. We formulate the disk two-point functions with ordinary and anisotropic boundary conditions as loop correlators in the matrix model. We derive the loop equations for these correlators and find their explicit solution in the scaling limit. Our solution reproduces the boundary phase diagram and the boundary critical exponents obtained recently by Dubail, Jacobsen and Saleur, except for the cusp at the isotropic special transition point. Moreover, our solution describes the bulk and the boundary deformations away from the anisotropic special transitions. In particular it shows how the anisotropic special boundary conditions are deformed by the bulk thermal flow towards the dense phase.

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