Instanton
= Instanton
{wiki}
An <instanton> is a localized finite-action classical solution in Euclidean spacetime, used in a semiclassical description of <quantum tunnelling> and other nonperturbative effects. In one-dimensional quantum mechanics it can connect distinct degenerate potential minima over infinite Euclidean time. A <quartic double-well instanton> is an elementary example; a <Yang-Mills instanton> is a gauge-field example with different geometric structure.