Prof. Dmitri Melikhov (HEPHY & SINP)
We study the decay constants of D, Ds, B, Bs mesons with Borel QCD sum rules, making use of the recent modifications related to the Borel-parameter-dependent effective continuum threshold. For the fixed values of the QCD parameters, our modifications are shown to lead to a visible shift of the extracted value of the decay constant compared to the standard analysis based on a Borel-parameter-independent threshold. We argue that our modifications allow one to probe the systematic errors of the extracted decay constants. We provide rather accurate results for fD and fDs. We demonstrate that an accurate extraction of fB and fBs is only possible if a very precise value of m_b(m_b) is known.