$D-\bar D$ mixing in the framework of the HQE revisited

We reconsider the leading HQE contributions to the absorptive part of the mixing amplitude of neutral $D$ mesons by taking also $\alpha_s$ corrections and subleading $1/m_c$ corrections into account. We show that these contributions to $\Gamma_{12}$ do not vanish in the exact SU(3)$_F$ limit and they also can have a large phase. Moreover, we give an example of a new physics model that can enhance these leading HQE terms to $\Gamma_{12}$, which are orders of magnitude lower than the current experimental expectation, by a factor in the upper double-digit range.