Matrix elements of four-fermion operators in the HQET

The B-B̄ mixing, B-meson lifetimes, the Bs-B̄s lifetime difference and SUSY FCNC effects in ∆B = 2 processes are very important measurable quantities in B-meson phenomenology whose theoretical predictions depend on unknown matrix elements of several four–fermion operators. We present preliminary results for the matrix elements of the relevant four–fermion operators computed on a sample of 600 lattices of size 24 × 40 at β = 6.0, using the SW–Clover action for light quarks with rotated light quark propagators and the lattice version of the HQET for heavy quarks. As a necessary ingredient of the calculation, we also present results for the next-to-leading order matching of the full theory to the lattice HQET (oneand two–loop anomalous dimensions, one–loop QCD-HQET matching coefficients and one–loop continuum-lattice HQET matching coefficients).