Non-leptonic decays in an extended chiral quark model

We consider the color suppressed (nonfactorizable) amplitude for the decay mode $\bar{B_{d}^0} \rightarrow \pi^0 \pi^{0}$. We treat the $b$-quark in the heavy quark limit and the energetic light ($u,d,s$) quarks within a variant of Large Energy Effective Theory combined with an extension of chiral quark models. Our calculated amplitude for $\bar{B_{d}^0} \rightarrow \pi^0 \pi^{0}$ is suppressed by a factor of order $\Lambda_{QCD}/m_b$ with respect to the factorized amplitude, as it should according to QCD-factorization. Further, for reasonable values of the (model dependent) gluon condensate and the constituent quark mass, the calculated nonfactorizable amplitude for $\bar{B_{d}^0} \rightarrow \pi^0 \pi^{0}$ can easily accomodate the experimental value. Unfortunately, the color suppressed amplitude is very sensitive to the values of these model dependent parameters. Therefore fine-tuning is necessary in order to obtain an amplitude compatible with the experimental result for $\bar{B_{d}^0} \rightarrow \pi^0 \pi^{0}$.Comment: 10 pages, 6 figures. Presented at QCD@work, Lecce, Italy, june 201

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

The double radiative annihilation of the heavy-light fermion bound states

We consider the double-radiative decays of heavy-light QED and QCD atoms, $\mu^+ e^- \to \gamma\gamma$ and $\bar{B}^{0}_s \to \gamma\gamma$. Especially, we take under scrutiny contributions coming from operators that vanish on the free-quark mass shell. We show that by field redefinitions these operators are converted into contact terms attached to the bound state dynamics. A net off-shell contribution is suppressed with respect to the effect of the well known flavour-changing magnetic-moment operator by the bound-state binding factor. The negligible off-shellness of the weakly bound QED atoms becomes more relevant for strongly bound QCD atoms. We analyze this off-shellness in model-approaches to QCD, one of them enabling us to keep close contact to the related effect in QED. We also comment on the off-shell effect in the corresponding process $\bar{B}_d \to K^* \gamma$, and discuss possible hindering of the claimed beyond-standard-model discovery in this decay mode.Comment: 24 pages, 5 figures; to be published in Fizika