The exclusive B_s\rightarrow \phi \ell^+ \ell^- decay in the two Higgs doublet models

We study the differential branching ratio, the branching ratio and the forward-backward asymmetry for exclusive decay in the two Higgs doublet model. We analyze the dependences of these quantities on the model parameters and show that these observables are highly sensitive to new physics and hence may provide a powerful probe of the SM and beyond. Received: 27 March 2002 / Revised version: 3 July 2002 / Published online: 20 September 2002 RID="a" ID="a" e-mail: gurerk@newton.physics.metu.edu.tr RID="b" ID="b" e-mail: gsevgur@metu.edu.tr     

Double-lepton polarization asymmetries in the $B \to K \ell^ + \ell^-$ decaybeyond the standard model

General expressions for the double-lepton polarizations in the decay are obtained, using a model independent effective Hamiltonian, including all possible interactions. Correlations between the averaged double-lepton polarization asymmetries and the branching ratio, as well as the averaged single-lepton polarization asymmetry are studied. It is observed that a study of the double-lepton polarization asymmetries can serve as a good test for establishing new physics beyond the standard model.Received: 23 November 2003, Revised: 8 March 2004, Published online: 30 April 2004     

General analysis of CP-violation in polarized $b \rightarrow d \ell^ + \ell^-$ decay

The CP-violating asymmetries in the decay, when one of the leptons is polarized, is investigated using the most general form of the effective Hamiltonian. The sensitivity of the CP-violating asymmetries to the new Wilson coefficients is studied.Received: 23 August 2003, Published online: 4 November 2003     

CP violation in \Lambda_b \to p \pi^- decay

Using the next-to-leading order QCD corrected effective Hamiltonian, scale and scheme independent Wilson coefficients, we have estimated the branching ratio and CP violating asymmetries for the decay mode in the Standard Model using the framework of generalized factorization. The effects of nonfactorizable contributions are taken into account by treating the effective no. of colors as a free parameter. The form factors are evaluated in the nonrelativistic quark model. The estimated branching ratio is found to be which lies below the current experimental upper limit and the CP violating asymmetries are and . Received: 15 February 2000 / Published online: 8 June 2000     

Rare $$\Lambda _c\rightarrow p \ell ^+\ell ^-$$ decay in the relativistic quark model

The relativistic quark model based on the quasipotential approach with the QCD-motivate potential is employed for the calculation of the form factors of the \(\Lambda _c\rightarrow p\) rare weak transitions. Their momentum dependence is explicitly determined without additional assumptions and extrapolations in the whole kinematical range of the momentum transfer squared \(q^2\). The differential \(\Lambda _c\rightarrow p l^+l^-\) decay branching fractions and angular distributions are calculated on the basis of these form factors. Both the perturbative and effective Wilson coefficients, which include contributions of vector meson resonances, are used. The calculated branching fraction of the \(\Lambda _c\rightarrow p \mu ^+\mu ^-\) rare decay is well consistent with the experimental upper limit very recently set by the LHCb Collaboration.     

Lepton polarization asymmetries in rare semi-tauonic $$ b \rightarrow s $$ exclusive decays at FCC- ee

We consider measurements of exclusive rare semi-tauonic b-hadron decays, mediated by the \(b \rightarrow s \tau ^+ \tau ^-\) transition, at a future high-energy circular electron–positron collider (FCC-ee). We argue that the high boosts of b-hadrons originating from on-shell Z boson decays allow for a full reconstruction of the decay kinematics in hadronic \(\tau \) decay modes (up to discrete ambiguities). This, together with the potentially large statistics of \(Z\rightarrow b\bar{b}\), opens the door for the experimental determination of \(\tau \) polarizations in these rare b-hadron decays. In the light of the current experimental situation on lepton flavor universality in rare semileptonic B decays, we discuss the complementary short-distance physics information carried by the \(\tau \) polarizations and suggest suitable theoretically clean observables in the form of single- and double-\(\tau \) polarization asymmetries.     

\mu\rightarrow e\gamma decay in the left-right supersymmetric model

We calculate the dipole amplitude for the decay and related processes in the left-right supersymmetric model when parity breaking occurs at a considerably large scale. The low-energy flavor violation in the model originates either from the nonvanishing remnants of the left-right symmetry in the slepton mass matrix or from the direct flavor changing lepton-slepton-neutralino interaction. The result is found to be large and already accessible with current experimental accuracy for supersymmetric masses not far above the electroweak scale. It also provides nontrivial constraints on the lepton mixing in the model. Received: 8 June 1998 / Published online: 15 October 1998