arXiv:1503.08688 · Physical Review B
Higgs amplitude mode in the vicinity of a (2+1) -dimensional quantum critical point: A nonperturbative renormalization-group approach
Félix Rose, F. Léonard, N. Dupuis
Abstract
We study the ``Higgs'' amplitude mode in the relativistic quantum $\mathrm{O}(N)$ model in two space dimensions. Using the nonperturbative renormalization group and the Blaizot--M\'endez-Galain--Wschebor approximation (which we generalize to compute four-point correlation functions), we compute the $\mathrm{O}(N)$-invariant scalar susceptibility at zero temperature in the vicinity of the quantum critical point. In the ordered phase, we find a well-defined Higgs resonance for $N=2$ and 3 and determine its universal properties. No resonance is found for $N\ensuremath{\ge}4$. In the disordered phase, the spectral function exhibits a threshold behavior with no Higgs-like peak. We also show that for $N=2$, the Higgs mode manifests itself as a very broad peak in the longitudinal susceptibility in spite of the infrared divergence of the latter. We compare our findings with results from quantum Monte Carlo simulations and $\ensuremath{\epsilon}=4\ensuremath{-}(d+1)$ expansion near $d=3$.