Universal persistent currents in mesoscopic metal rings due to long-range Coulomb interactions

We calculate the average persistent current in a mesoscopic metal ring threaded by a magnetic flux in the diffusive regime. It is shown that the classical electromagnetic energy leads to a {\it{universal}} average current of the order of $ \alpha e c / C_{0}$, where $\alpha$ is the fine structure constant, $-e$ is the charge of the electron, $c$ is the velocity of light, and $C_{0}$ is the classical capacitance of the ring. Striking similarities between persistent currents and universal conductance fluctuations are discovered. We suggest a simple experiment to test our theory.