 Yang-Mills instanton

A Yang-Mills instanton is a finite-action Euclidean gauge field with self-dual or anti-self-dual curvature. On ${\mathbb{R}}^4$, its asymptotic pure gauge defines a map $S_{\infty }^3\to SU(2)$ whose degree is the instanton number.

It is a gauge-field instanton solving the Euclidean Yang-Mills equations, with additional finite-action and duality conditions.