Hamiltonian Truncation with Larger Dimensions

Abstract: Hamiltonian Truncation (HT) is a numerical approach for calculating observables in a Quantum Field Theory non-perturbatively. This approach can be applied to theories constructed by deforming a conformal field theory with a relevant operator of scaling dimension $\Delta$. UV divergences arise when $\Delta$ is larger than half of the spacetime dimension $d$. These divergences can be regulated by HT or by using a more conventional local regulator. In this work we show that extra UV divergences appear when using HT rather than a local regulator for $\Delta \geq d/2+1/4$, revealing a striking breakdown of locality. Our claim is based on the analysis of conformal perturbation theory up to fourth order. As an example we compute the Casimir energy of $d=2$ Minimal Models perturbed by operators whose dimensions take values on either side of the threshold $d/2+1/4$.