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

TL;DR

This paper investigates the inhomogeneous chiral condensate phase in the Gross-Neveu model across non-integer spatial dimensions, revealing its presence below dimension 2 and its absence at and above 2, thus connecting known results in 1, 2, and 3 dimensions.

Contribution

The study extends the analysis of the Gross-Neveu model to non-integer dimensions, showing the inhomogeneous phase exists for all dimensions less than 2 and disappears at dimension 2.

Findings

Inhomogeneous phase exists for all d<2

Phase vanishes exactly at d=2

No instability towards inhomogeneous phase for 2≤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 $1 \leq d <3$, 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 $2\leq d<3$, which suggests that the IP in $d=3$ is solely generated by the presence of a regulator.