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Symmetric boundary conditions in boundary critical phenomena

Philippe Ruelle

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Conformally invariant boundary conditions for minimal models on a cylinder are classified by pairs of Lie algebras (A,G) of ADE type. For each model, we consider the action of its (discrete) symmetry group on the boundary conditions. We find that the invariant ones correspond to nodes in the product graph A × G that are fixed by some automorphism. We proceed to determine the charges of the fields in the various Hilbert spaces, but, in a general minimal model, many consistent solutions occur. In the unitary models (A,A), we show that there is a unique solution with the property that the ground state in each sector of boundary conditions is invariant under the symmetry group. In contrast, a solution with this property does not exist in the unitary models of the series (A,D) and (A,E6). A tempting interpretation of this fact is that a certain (large) number of invariant boundary conditions have unphysical (negative) classical boundary Boltzmann weights. We give a tentative characterization of the problematic boundary conditions.


PACS

02.20.Sv Lie algebras of Lie groups

02.30.Lt Sequences, series, and summability

MSC

82B27 Critical phenomena

22E60 Lie algebras of Lie groups (For the algebraic theory of Lie algebras, see 17Bxx)

Subjects

Mathematical physics

Dates

Issue 50 (17 December 1999)

Received 12 July 1999



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