On the gauge-invariant dynamical charges and densities of the 1-instanton solution

Abstract

We study the gauge-invariant dynamically conserved charges, and their corresponding densities, for instanton solutions of Yang-Mills theories in four dimensional Euclidean space, for the gauge group $SU(2)$. Those charges were constructed in [1,2] through the integral equations of Yang-Mills theory, using techniques on generalized loop spaces. We use the integral non-Abelian Gauss law to evaluate the gauge-invariant flux of the magnetic and electric non-Abelian fields through spherical surfaces centered at the origin of the instanton solution. From such a flux, we define gauge-invariant charge densities by considering the charge within an infinitesimal spherical shell of radius $r\equiv \sqrt{x_i{x}^i}/\lambda$, with $\lambda$ being the parameter of the instanton solution, defining its size, and $x_i{x}^i=(x^1{)}^2+(x^2{)}^2+(x^3{)}^2$. We discuss the issue of the reparameterization invariance of the charges and densities, and show that the magnetic and electric fluxes for the instanton and anti-instanton, at $r=1$ and $x^4=0$, $x^4$ being the Euclidean time, are non-zero and observable. Our results give an interesting picture of the internal structure of the instanton, and may be important for the properties of the Yang-Mills $\theta$-vacuum.

43 pages, 6 figures, Version published in Open Communications in Nonlinear Mathematical Physics, Special Issue Hietarinta 2026, ocnmp:18516, pp 141-183