Yang-Mills instanton
= Yang-Mills instanton
{c}
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 $S^3_\infty\to SU(2)$ 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.