Nonabelian alpha_s³/(m_q r²) heavy-quark-antiquark potential

We calculate the leading mass-suppressed two-loop contribution, proportional to alpha_s^3/(m_q r^2), to the potential of a heavy quark-antiquark system. This contribution originates in the nonabelian nature of quantum chromodynamics (QCD) and has no analogue in quantum electrodynamics (QED). For this purpose, we elaborate a technique based on the implementation of the threshold expansion within the effective theory of nonrelativistic QCD (NRQCD). We discuss phenomenological implications of our result for heavy-quarkonium physics. We also confirm a previous result for the two-loop O(alpha_s^2) correction to the static potential.