The renormalisation group for the truncated conformal space approach on the cylinder

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In this paper we continue the study of the truncated conformal space approach to perturbed conformal field theories, this time applied to bulk perturbations and focusing on the leading truncation-dependent corrections to the spectrum.

• We find expressions for the leading terms in the ground state energy divergence, the coupling constant renormalisation and the energy rescaling.
• We apply these methods to problems treated in two seminal papers and show how these RG improvements greatly increase the predictive power of the TCSA approach.
• One important outcome is that the TCSA spectrum of excitations is predicted not to converge for perturbations of conformal weight greater than 3/4, but the ratios of excitation energies should converge.