John Michael Cornwall (born 19 August 1934 in Denver, Colorado) is an American theoretical physicist who does research on elementary particle physics and quantum field theory as well as geophysics and physics of near-space.
He graduated in 1962 from the University of California, Berkeley with a doctorate under the supervision of Malvin Ruderman.
Cornwall invented the Pinch Technique for calculating gauge-invariant off-shell Green's functions for QCD and other Yang-Mills theories, showing how a dynamical gauge-invariant mass arises for QCD gluons and how such gluons, with the long-range pure-gauge fields that necessarily accompany gauge-invariant mass generation, lead to confinement and other non-perturbative phenomena.
He has also written some 40 papers on space plasmas such as the aurora, the ionosphere, and the magnetospheric ring current, leading among other things to a detailed understanding of the dynamical role of electromagnetic cyclotron instabilities in the magnetosphere.Cornwall published with Richard E. Norton in 1973 one of the earliest papers on dynamic symmetry breaking in Yang-Mills theories.
He was a visiting professor for the academic year 1987–1988 at the Massachusetts Institute of Technology and in 1989 at Rockefeller University.