Title: High-Precision Calculations in Strongly Coupled Quantum Field Theory with Next-to-Leading-Order Renormalized Hamiltonian Truncation,
Abstract: Hamiltonian Truncation (a.k.a. Truncated Spectrum Approach) is an efficient
numerical technique to solve strongly coupled QFTs in d=2 spacetime dimensions.
Further theoretical developments are needed to increase its accuracy and the
range of applicability. With this goal in mind, here we present a new variant
of Hamiltonian Truncation which exhibits smaller dependence on the UV cutoff
than other existing implementations, and yields more accurate spectra. The key
idea for achieving this consists in integrating out exactly a certain class of
high energy states, which corresponds to performing renormalization at the
cubic order in the interaction strength. We test the new method on the strongly
coupled two-dimensional quartic scalar theory. Our work will also be useful for
the future goal of extending Hamiltonian Truncation to higher dimensions d >=
3.