  In the framework of nonrelativistic QCD, we consider a new class of radiative
corrections, which are generated at next-to-next-to-next-to-leading order
through the chromoelectric dipole interaction of heavy quarkonium with
ultrasoft virtual gluons. We provide analytical formulae from which the
resulting shifts in the quarkonium energy levels and the wave functions at the
origin may be calculated. We discuss the phenomenological implications for the
top-antitop and Upsilon systems and point out some limitations of describing
charmonium using a Coulomb potential.

High Energy Physics - Phenomenology