Jackiw is famous for the discovery of the so-called axial anomaly, also known as Adler–Bell–Jackiw anomaly, also known as the chiral anomaly. In 1969, Roman Jackiw and John Stewart Bell published their explanation, which was later expanded and clarified by Stephen L. Adler, of the (observed) decay of a neutral pion into two photons. This decay is forbidden by a symmetry of classical electrodynamics, but Bell and Jackiw showed that this symmetry cannot be preserved at the quantum level.