Non-factorizable contributions to Bd0ˉ→Ds(∗)Ds(∗)ˉ\bar{B^0_d} \to D_s^{(*)} \bar{D_s^{(*)}}

It is pointed out that decays of the type $B \to D \bar{D}$ have no factorizable contributions, unless at least one of the charmed mesons in the final state is a vector meson. The dominant contributions to the decay amplitudes arise from chiral loop contributions and tree level amplitudes generated by soft gluon emissions forming a gluon condensate. We predict that the branching ratios for the processes $\bar B^0 \to D_s^+ D_s^-$, $\bar B^0 \to D_s^{+*} D_s^-$ and $\bar B^0 \to D_s^+ D_s^{-*}$ are all of order $(3- 4) \times 10^{-4}$, while $\bar B^0 \to D_s^{+*} D_s^{-*}$ has a branching ratio 5 to 10 times bigger. We emphasize that the branching ratios are sensitive to $1/m_c$ corrections.Comment: 4 pages, 4 figures. Based on talk by J.O. Eeg at BEACH 2004, 6th international conference on Hyperons, Charm and Beauty Hadrons, Illionois Institute of Technology, Chicago, june. 27 - july 3, 200

The self-penguin contribution to K→2πK \to 2 \pi

We consider the contribution to $K \rightarrow 2 \pi$ decays from the non-diagonal s \ra d quark transition amplitude. First, we calculate the most important part of the $s \rightarrow d$ transition, the so-called self-penguin amplitude $\sim G_F \alpha_s$, including the heavy top-quark case. Second, we calculate the matrix element of the $s \rightarrow d$ transition for the physical $K \rightarrow 2 \pi$ process. This part of the analysis is performed within the Chiral Quark Model where quarks are coupled to the pseudoscalar mesons. The CP-conserving self-penguin contribution to $K \rightarrow 2\pi$ is found to be negligible. The obtained contribution to $\epsilon'/\epsilon$ is sensitive to the values of the quark condensate $$ and the constituent quark mass $M$. For reasonable values of these quantities we find that the self-penguin contribution to $\epsilon'/\epsilon$ is 10-15% of the gluonic penguin contribution and has the same sign. Given the large cancellation between gluonic and electroweak penguin contributions, this means that our contribution is of the same order of magnitude as $\epsilon'/\epsilon$ itself.Comment: Latex, 12 pages, 2 figure

A Heavy-Light Chiral Quark Model

We present a new chiral quark model for mesons involving a heavy and a light (anti-) quark. The model relates various combinations of a quark - meson coupling constant and loop integrals to physical quantities. Then, some quantities may be predicted and some used as input. The extension from other similar models is that the present model includes the lowest order gluon condensate of the order (300 MeV)^4 determined by the mass splitting of the 0^- and the 1^- heavy meson states. Within the model, we find a reasonable description of parameters such as the decay constants f_B and f_D, the Isgur-Wise function and the axial vector coupling g_A in chiral perturbation theory for light and heavy mesons.Comment: 31 pages, 13 figures, RevTex4.

Soft end-point and mass corrections to the eta' g*g* vertex function

Power-suppressed corrections arising from end-point integration regions to the space-like vertex function of the massive eta'-meson virtual gluon transition eta' - g*g* are computed. Calculations are performed within the standard hard-scattering approach (HSA) and the running coupling method supplemented by the infrared renormalon calculus. Contributions to the vertex function from the quark and gluon contents of the eta' -meson are taken into account and the Borel resummed expressions for F_{eta' g*g*}(Q2,\omega ,\eta), as well as for F_{eta' g g*}}(Q^{2},\omega =\pm 1,\eta) and F_{eta' g*g*}(Q^{2},\omega =0,\eta) are obtained. It is demonstrated that the power-suppressed corrections \sim (\Lambda ^{2}/Q^{2})^{n}, in the explored range of the total gluon virtuality 1 <Q2 < 25 GeV2, considerably enhance the vertex function relative to the results found in the framework of the standard HSA with a fixed coupling. Modifications generated by the eta ' -meson mass effects are discussed

A New Estimate of ε′/ε\varepsilon '/\varepsilon

We discuss direct $CP$ violation in the standard model by giving a new estimate of $\varepsilon'/\varepsilon$ in kaon decays. Our analysis is based on the evaluation of the hadronic matrix elements of the \mbox{$\Delta S =1$} effective quark lagrangian by means of the chiral quark model, with the inclusion of meson one-loop renormalization and NLO Wilson coefficients. Our estimate is fully consistent with the $\Delta I =1/2$ selection rule in $K\to \pi\pi$ decays which is well reproduced within the same framework. By varying all parameters in the allowed ranges and, in particular, taking the quark condensate---which is the major source of uncertainty---between $(-200\ {\rm MeV})^3$ and $(-280\ {\rm MeV})^3$ we find $$-5.0 \times 10^{-3}\ <\varepsilon'/\varepsilon <\ 1.4 \times 10^{-3}\ .$$ Assuming for the quark condensate the improved PCAC result \mbox{\vev{\bar qq} = -(221\: \pm 17\ {\rm MeV})^3} and fixing $\Lambda_{\rm QCD}^{(4)}$ to its central value, we find the more restrictive prediction $$\varepsilon '/\varepsilon = ( 4 \pm 5 ) \,\times \,10^{-4}\ ,$$ where the central value is defined as the average over the allowed values of Im $\lambda_t$ in the first and second quadrants. In these estimates the relevant mixing parameter Im $\lambda_t$ is self-consistently obtained from $\varepsilon$ and we take $m_t^{\rm pole} = 180 \pm 12$ GeV. Our result is, to a very good approximation, renormalization-scale and $\gamma_5$-scheme independent.Comment: 40 pages, uuencoded LATEX2e file including 13 eps figures, revised version to appear in Nucl. Phys.

A QCD Sum Rule Approach to the s→dγs\to d\gamma Contribution to the Ω−→Ξ−γ\Omega^-\to \Xi^-\gamma Radiative Decay

QCD sum rules are used to calculate the contribution of short-distance single-quark transition $s\rightarrow d \gamma$, to the amplitudes of the hyperon radiative decay, $\Omega^-\rightarrow \Xi^-\gamma$. We re-evaluate the Wilson coefficient of the effective operator responsible for this transition. We obtain a branching ratio which is comparable to the unitarity limit.Comment: 15 pages, Revtex, 13 figures available as a uuencoded, gz-compressed ps fil

Long Distance Contribution to s→dγs \to d\gamma and Implications for Ω−→Ξ−γ,Bs→Bd∗γ\Omega^-\to \Xi ^-\gamma, B_s \to B_d^*\gamma and b→sγb \to s\gamma

We estimate the long distance (LD) contribution to the magnetic part of the $s \to d\gamma$ transition using the Vector Meson Dominance approximation $(V=\rho,\omega,\psi_i)$. We find that this contribution may be significantly larger than the short distance (SD) contribution to $s \to d\gamma$ and could possibly saturate the present experimental upper bound on the $\Omega^-\to \Xi^-\gamma$ decay rate, $\Gamma^{\rm MAX}_{\Omega^-\to \Xi^-\gamma} \simeq 3.7\times10^{-9}$eV. For the decay $B_s \to B^*_d\gamma$, which is driven by $s \to d\gamma$ as well, we obtain an upper bound on the branching ratio $BR(B_s \to B_d^*\gamma)<3\times10^{-8}$ from $\Gamma^{\rm MAX}_{\Omega^-\to \Xi^-\gamma}$. Barring the possibility that the Quantum Chromodynamics coefficient $a_2(m_s)$ be much smaller than 1, $\Gamma^{\rm MAX}_{\Omega^-\to \Xi^-\gamma}$ also implies the approximate relation $\frac{2}{3} \sum_i \frac{g^2_{\psi_i}(0)}{m^2_{\psi_i}} \simeq \frac{1}{2} \frac{g^2_\rho(0)}{m^2_\rho} + \frac{1}{6}\frac{g^2_\omega(0)}{m^2_\omega}$. This relation agrees quantitatively with a recent independent estimate of the l.h.s. by Deshpande et al., confirming that the LD contributions to $b \to s\gamma$ are small. We find that these amount to an increase of $(4\pm2)\%$ in the magnitude of the $b \to s \gamma$ transition amplitude, relative to the SD contribution alone.Comment: 16 pages, LaTeX fil

On the short-distance constraints from K_{L,S} -> mu^+ mu^-

Motivated by new precise results on several $K_L$ decays, sensitive to the ${K_L \to \gamma \gamma}$ form factor, we present a new analysis of the $K_L\to \mu^+\mu^-$ long-distance amplitude based on a semi-phenomenological approach. Particular attention is devoted to the evaluation of the uncertainties of this method and to the comparison with alternative approaches. Our main result is a conservative upper bound of $2.5 \times 10^{-9}$ on $B(K_L \to \mu^+ \mu^-)_{\rm short}$, which is compatible with the SM expectation and which provides significant constraints on new-physics scenarios. The possibility to extract an independent short-distance information from future searches on $K_S \to \mu^+ \mu^-$ is also briefly discussed.Comment: 16 pages, 4 figures, late

The ΔS=1\Delta S = 1 Weak Chiral Lagrangian as the Effective Theory of the Chiral Quark Model

We use the chiral quark model to estimate the coefficients of the weak chiral lagrangian as obtained from the bosonization of the ten relevant operators of the $\Delta S = 1$ effective quark lagrangian. All contributions of order $N_c^2$ as well as $N_c$ and $\alpha_s N_c$ are included. The chiral coefficients are given in terms of $f_{\pi}$, the quark and gluon condensates and the scale-dependent NLO Wilson coefficients of the corresponding operators. In addition, they depend on the constituent quark mass $M$, a parameter characteristic of the model. The $\gamma_5$-scheme dependence of the chiral coefficients, computed via dimensional regularization, and the Fierz transformation properties of the operator basis are discussed in detail. We apply our result to the evaluation of the hadronic matrix elements for the decay $K^0 \rightarrow 2 \pi$, consistently including the renormalization induced by the meson loops. The effect of this renormalization is sizable and introduces a long-distance scale dependence that matches in the physical amplitudes the short-distance scale dependence of the Wilson coefficients.Comment: Revised version to appear in Nucl. Phys. B 48 pages, uuencoded LATEX file including 4 eps figure

Lepton Flavour Violating Leptonic/Semileptonic Decays of Charged Leptons in the Minimal Supersymmetric Standard Model

We consider the leptonic and semileptonic (SL) lepton flavour violating (LFV) decays of the charged leptons in the minimal supersymmetric standard model (MSSM). The formalism for evaluation of branching fractions for the SL LFV charged-lepton decays with one or two pseudoscalar mesons, or one vector meson in the final state, is given. Previous amplitudes for the SL LFV charged-lepton decays in MSSM are improved, for instance the $\gamma$-penguin amplitude is corrected to assure the gauge invariance. The decays are studied not only in the model-independent formulation of the theory in the frame of MSSM, but also within the frame of the minimal supersymmetric SO(10) model within which the parameters of the MSSM are determined. The latter model gives predictions for the neutrino-Dirac Yukawa coupling matrix, once free parameters in the model are appropriately fixed to accommodate the recent neutrino oscillation data. Using this unambiguous neutrino-Dirac Yukawa couplings, we calculate the LFV leptonic and SL decay processes assuming the minimal supergravity scenario. A very detailed numerical analysis is done to constrain the MSSM parameters. Numerical results for SL LFV processes are given, for instance for tau -> e (mu) pi0, tau -> e (mu) eta, tau -> e (mu) eta', tau -> e (mu) rho0, tau -> e (mu) phi, tau -> e (mu) omega, etc.Comment: 36 pages, 3 tables, 5 .eps figure