Higgs mode in (2 + 1)-dimensional O(2) model

In this paper, we investigate the spectral functions of Higgs mode in [Formula: see text] model, which can be experimentally realized a two-dimensional Bose gas. Zero temperature limit is considered. Our calculation fully includes 2-loop contributions. Peaks show up both longitudinal and scalar susceptibilities. Thus, model cannot explain disappearance response at weak interaction limit. Neither it similarity between susceptibilities visibility mode. A possible lower peak about also noted.