Exact string potential and heavy quarkonia

Using the exact form of the static string potential we reinvestigate previous potential-model calculations of the energy levels of $q\overline{q}$ resonances. We show the effect of higher-order corrections to strings on the quarkonium spectroscopy and the leptonic decays of the $\Upsilon$ and $\frac{J}{\psi }$ where we find that the roughened form of the string potential has a significant effect. We also propose a new form of the potential which incorporates both the quantum effects and asymptotic freedom.