Conformal Windows beyond Asymptotic Freedom

TL;DR

This paper investigates the existence and properties of conformal fixed points in four-dimensional gauge theories with fermions and scalars, especially beyond the asymptotic freedom regime, revealing a narrowed conformal window and new fixed points.

Contribution

It provides a comprehensive perturbative analysis of fixed points in gauge theories with scalars and fermions beyond the Veneziano limit, including finite-N corrections and phase diagram insights.

Findings

Identification of a new infrared fixed point with detailed properties.

Conformal window is narrowed by finite-N effects.

No clear evidence of new fixed points at large N_f beyond weak coupling.

Abstract

We study four-dimensional gauge theories coupled to fermions in the fundamental and meson-like scalars. All requisite beta functions are provided for general gauge group and fermion representation. In the regime where asymptotic freedom is absent, we determine all interacting fixed points using perturbation theory up to three loop in the gauge and two loop in the Yukawa and quartic couplings. We find that the conformal window of ultraviolet fixed points is narrowed-down by finite-$N$ corrections beyond the Veneziano limit. We also find a new infrared fixed point whose main features such as scaling exponents, UV-IR connecting trajectories, and phase diagram are provided. Both fixed points collide upon varying the number of fermion flavours $N_{\rm f}$, and conformality is lost through a saddle-node bifurcation. We further revisit the prospect for ultraviolet fixed points in the large $N_{\rm f}$ limit where matter field fluctuations dominate. Unlike at weak coupling, we do not find clear evidence for new scaling solutions even in the presence of scalar and Yukawa couplings.