Dominant 1/m_c Contribution To The Mass Difference in D0-D0bar Mixing

We re-visit the problem of non-perturbative contribution to the mass difference in D0-D0bar mixing within the Standard Model (SM). There are two known approaches to take this contribution into account. In the long long-distance approach one analyzes contribution to the D0-D0bar from exclusive channels due to production of intermediate charmless hadronic states. In the short-distance approach one employs the Operator Product Expansion (OPE) techniques with the non-perturbative contribution coming from the diagrams containing low energy-momentum quark states - quark-antiquark condensates. Within the latter approach, the non-perturbative contribution to the normalized mass difference in D0-D0bar mixing, x_D = Delta M_D / Gamma_D, is estimated to be few x 10^{-3}, that is to say very close to the experimental value of x_D. We attempt to verify quantitatively this estimate here. We find that the actual prediction of the short-distance approach is few times less than the estimate above and order of magnitude less than the experimental value of x_D.