The Baryon Wilson Loop Area Law in QCD

TL;DR

This paper clarifies the correct area law for the baryonic Wilson loop in QCD, deriving the $ riangle$ law from vortex-monopole models and reconciling it with lattice and strong-coupling approximations.

Contribution

The paper derives the $ riangle$ law for the baryonic Wilson loop from vortex-monopole models and connects it with non-Abelian Stokes' theorem, resolving previous ambiguities.

Findings

The $ riangle$ law leads to a larger Wilson loop value than the $Y$ law.

Strong-coupling surfaces persist as surfaces in the non-Abelian Stokes' theorem.

The derivation extends to $SU(N)$ gauge groups with $N>3$.

Abstract

There is still confusion about the correct form of the area law for the baryonic Wilson loop (BWL) of QCD. Strong-coupling (i.e., finite lattice spacing in lattice gauge theory) approximations suggest the form $\exp [-KA_Y]$, where $K$ is the $q\bar{q}$ string tension and $A_Y$ is the global minimum area, generically a three-bladed area with the blades joined along a Steiner line ($Y$ configuration). However, the correct answer is $\exp[-(K/2)(A_{12}+A_{13}+A_{23})]$, where, e.g., $A_{12}$ is the minimal area between quark lines 1 and 2 ($\Delta$ configuration). This second answer was given long ago, based on certain approximations, and is also strongly favored in lattice computations. In the present work, we derive the $\Delta$ law from the usual vortex-monopole picture of confine- ment, and show that in any case because of the 1/2 in the $\Delta$ law, this law leads to a larger value for the BWL (smaller exponent) than does the $Y$ law. We show that the three-bladed strong-coupling surfaces, which are infinitesimally thick in the limit of zero lattice spacing, survive as surfaces to be used in the non-Abelian Stokes' theorem for the BWL, which we derive, and lead via this Stokes' theorem to the correct $\Delta$ law. Finally, we extend these considerations, including perturbative contributions, to gauge groups $SU(N)$, with $N>3$.