Long distances effects in the hyperfine splittings of heavy quarkonium hybrids

We report on a calculation of the hyperfine splitting of heavy quarkonium hybrids, which takes into account the long-distance form of the heavy-quark spin-dependent potentials. These potenetials are estimated using an interpolation between the known short-distance form and the long distance form calculated in the QCD effective string theory. We correct an error in the long distance form of one of the potentials used before, which leads to very small modifications of the previous results.