Finite size effects in boundary sine-Gordon theory

We examine the finite volume spectrum and boundary energy in boundary sine-Gordon theory, based on our recent results obtained by closing the boundary bootstrap. The spectrum and the reflection factors are checked against truncated conformal space, together with a (still unpublished) prediction by Al.B. Zamolodchikov for the boundary energy and the relation between the parameters of the scattering amplitudes and of the perturbed CFT Hamiltonian. In addition, a derivation of Zamolodchikov's formulae is given. We find an entirely consistent picture and strong evidence for the validity of the conjectured spectrum and scattering amplitudes, which together give a complete description of the boundary sine-Gordon theory on mass shell. (C) 2002 Elsevier Science B.V. All rights reserved.