Symbol GW. 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 GW 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.