Non-factorizable effects in B-anti-B mixing

We study the B-parameter (``bag factor'') for B-anti-B mixing within a recently developed heavy-light chiral quark model. Non-factorizable contributions in terms of gluon condensates and chiral corrections are calculated. In addition, we also consider 1/m_Q corrections within heavy quark effective field theory. Perturbative QCD effects below \mu = m_b known from other work are also included. Considering two sets of input parameters, we find that the renormalization invariant B-parameter is B = 1.51 +- 0.09 for B_d and B = 1.40 +- 0.16 for B_s.Comment: 23 pages, 7 figures, RevTex 4 Small changes, included more details in the tex

The \beta-term for D^* --> D \gamma within a heavy-light chiral quark model

We present a calculation of the \beta-term for D^* --> D gamma within a heavy-light chiral quark model. Within the model, soft gluon effects in terms of the gluon condensate with lowest dimension are included. Also, calculations of 1/m_c corrections are performed. We find that the value of \beta is rather sensitive to the constituent quark mass compared to other quantities calculated within the same model. Also, to obtain a value close to the experimental value, one has to choose a constituent light quark mass larger than for other quantities studied in previous papers. For a light quark mass in the range 250 to 300 MeV and a quark condensate in the range -(250-270 MeV)^3 we find the value (2.5 +- 0.6) GeV^-1. This value is in agreement with the value of \beta extracted from experiment 2.7 +- 0.2 GeV^-1.Comment: 16 pages, 5 figure

On the Colour Suppressed Decay Modes B^0 --> D_s^+ D_s^- and B_s^0 --> D^+ D^-

We point out that the decay modes B^0 --> D_s^+ D_s^- and B_s^0 --> D^+ D^- have no factorized contribution. At quark level these dacays can only proceed through the annihilation mechanism, which in the factorized limit give zero amplitude due to current conservation. In this paper, we identify the dominating non-factorizable (colour suppressed) contributions in terms of two chiral loop contributions and one soft gluon emission contribution. The latter contribution can be calculated in terms of the (lowest dimension) gluon condensate within a recently developed heavy-light chiral quark model. We find braching ratios BR(B^0 --> D_s^+ D_s^-) = 7*10^-5 and BR(B^0_s --> D^+ D^-) = 1*10^-3.Comment: 13 pages, 4 figure