Inhomogeneous condensation in the Gross-Neveu model in noninteger spatial dimensions $1\le d<3$

Abstract

The Gross-Neveu model in the $N\to \infty$ approximation in $d=1$ spatial dimensions exhibits a chiral inhomogeneous phase (IP), where the chiral condensate has a spatial dependence that spontaneously breaks translational invariance and the ${\mathbb{Z}}_2$ chiral symmetry. This phase is absent in $d=2$, while in $d=3$ its existence and extent strongly depends on the regularization and the value of the finite regulator. This work connects these three results smoothly by extending the analysis to non-integer spatial dimensions $1\le d<3$, where the model is fully renormalizable. To this end, we adapt the stability analysis, which probes the stability of the homogeneous ground state under inhomogeneous perturbations, to non-integer spatial dimensions. We find that the IP is present for all $d<2$ and vanishes exactly at $d=2$. Moreover, we find no instability towards an IP for $2\le d<3$, which suggests that the IP in $d=3$ is solely generated by the presence of a regulator.

Comments: 14 pages, 6 figures. v2: corrected an error in the analysis for figure 6, version as accepted for publication in Physical Review D