Effect of irrelevant boundary scaling operators

We investigate the consequences of adding irrelevant (or less relevant) bou ndary operators to a (1+1)-dimensional field theory, using the Ising and th e boundary sine-Gordon model as examples. In the integrable case, irrelevan t perturbations are shown to multiply reflection matrices by Castillejo-Dal itz-Dyson factors: the low-energy behavior is not changed, while Various hi gh-energy behaviors are possible, including "roaming'' renormalization grou p trajectories. In the nonintegrable case, a Monte Carlo study shows that t he IR behavior is again generically unchanged, provided scaling variables a re appropriately renormalized. [S0163-1829(99)51132-6].