Ratios of B and D meson decay constants with heavy quark symmetry

摘要

SU(3) flavor symmetry allows the decay constants f_(D_s) and f_(D_d) as well as f_(B_s) and f_(B_d) to be equal. But due to SU(3) flavor symmetry breaking the ratios f_(B_s)/f_(B_d) and f_(D_s)/f_(D_d) are deviated from unity. We have estimated these ratios in the heavy quark effective theory and obtained f_(B_s)/f_(B_d) = 0.93, f_(D_s)/f_(D_d) = 0.94 and the double ratio (f_(B_s)/f_(B_d) )/(f_(D_s)/f_(D_d)) = 0.99.