title: Universal properties of the Higgs resonance in (2+1)-dimensional U(1) critical systems.
abstract: We present spectral functions for the magnitude squared of the order parameter in the scaling limit of the two-dimensional superfluid to Mott insulator quantum phase transition at constant density, which has emergent particle-hole symmetry and Lorentz invariance. The universal functions for the superfluid, Mott insulator, and normal liquid phases reveal a low-frequency resonance which is relatively sharp and is followed by a damped oscillation (in the first two phases only) before saturating to the quantum critical plateau. The counterintuitive resonance feature in the insulating and normal phases calls for deeper understanding of collective modes in the strongly coupled (2+1)-dimensional relativistic field theory. Our results are derived from analytically continued correlation functions obtained from path-integral Monte Carlo simulations of the Bose-Hubbard model.
authors.affiliation: National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Kun
authors.initials: K
authors.lastname: Chen
authors.forename: Longxiang
authors.initials: L
authors.lastname: Liu
authors.forename: Youjin
authors.initials: Y
authors.lastname: Deng
authors.forename: Lode
authors.initials: L
authors.lastname: Pollet
authors.forename: Nikolay
authors.initials: N
authors.lastname: Prokof'ev