Lower bound on the entropy of boundaries and junctions in (1+1)-dimensional quantum critical systems.

A lower bound is derived for the boundary entropy s=lng of a (1+1)-dimensional quantum critical system with boundary under the conditions c≥1 on the bulk conformal central charge and Δ1>(c-1)/12 on the most relevant bulk scaling dimension. This is the first general restriction on the possible values of g for bulk critical systems with c≥1.