Symbol G_W. The coupling constant associated with the weak interaction (see fundamental interactions), which gives rise to beta decay. The Fermi constant has a value 1.435×10⁻³⁶ joule metre³. The Fermi constant characterizes the Fermi theory of weak interactions. The dimensional nature of G_W means that the Fermi theory is limited to low energies and is unrenormalizable (see renormalization). This can be established by dimensional analysis for perturbation theory calculations of weak-interaction processes.