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

On Distinguishing Non-Standard Interactions from Radiative Corrections in Neutrino-Electron Scattering

We present a contribution of higher order to neutrino-electron scattering that is a charged-current counterpart of both the anomalous axial-vector triangle and possible non-standard interaction contributions. It arises in the standard model with massive neutrinos, and renormalizes the nondiagonal axial-vector form-factor at low energies. We show that, due to the small size of radiative corrections, the neutrino-electron scattering still provides a discovery potential for some of the non-standard neutrino interactions proposed in the literature.Comment: 9 pages, 3 figures, change in title and context of the consideration, results of radiative corrections unchange

New physics in \epsilon' from chromomagnetic contributions and limits on Left-Right symmetry

New physics in the chromomagnetic flavor changing transition s->dg* can avoid the strong GIM suppression of the Standard Model and lead to large contributions to CP-violating observables, in particular to the epsilon' parameter, that we address here. We discuss the case of the Left-Right symmetric models, where this contribution implies bounds on the phases of the right-handed quark mixing matrix, or in generic models with large phases a strong bound on the Left-Right symmetry scale. To the leading order, a numeric formula for epsilon' as a function of the short-distance coefficients for a wide class of models of new physics is given.Comment: 12 pages, Eq. 12 and related numerics amende

On the color suppressed contribution to $\bar{B_{d}^0} \rightarrow \, \pi^0 \pi^{0}

The decay modes of the type $B \rightarrow \pi \, \pi$ are dynamically different. For the case $\bar{B_{d}^0} \rightarrow \, \pi^+ \pi^-$ there is a substantial factorized contribution which dominates. In contrast, the decay mode $\bar{B_{d}^0} \rightarrow \, \pi^0 \pi^{0}$ has a small factorized contribution, being proportional to a small Wilson coefficient combination. However, for the decay mode $\bar{B_{d}^0} \rightarrow \, \pi^0 \pi^{0}$ there is a sizeable nonfactorizable (color suppressed) contribution due to soft (long distance) interactions, which dominate the amplitude. We estimate the branching ratio for the mode $\bar{B_{d}^0} \rightarrow \, \pi^0 \pi^{0}$ in the heavy quark limit for the $b$- quark. In order to estimate color suppressed contributions we treat the energetic light ($u,d,s$) quark within a variant of Large Energy Effective Theory combined with a recent extension of chiral quark models in terms of model- dependent gluon condensates. We find that our calculated color suppressed amplitude is suppressed by a factor of order $\Lambda_{QCD}/m_b$ with respect to the factorizable amplitude, as it should according to QCD-factorization. Further, for reasonable values of the constituent quark mass and the gluon condensate, 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 $\bar{B_{d}^0} \rightarrow \, \pi^0 \pi^{0}$. A possible link to the triangle anomaly is discussed.Comment: The submitted Latex version correspond to 23 pages in ps-version and contains 4 figure