We investigate the influence of the fourth generation of quarks on the branching ratio, the CP-asymmetry and the polarization asymmetries in $B \rar ρ\ell^+ \ell^-$ decay. Taking $|V_{t'd}V_{t'b}|\sim 0.001$ with phase about $10^\circ$, which is consistent with the $sin2ϕ_1$ of the CKM and the $B_d$ mixing parameter $Δm_{B_d}$, we obtain that for both ($μ, τ$) channels the branching ratio is increased and the magnitude of CP-asymmetry and polarization asymmetries decreased by the mass and mixing parameters of the 4th generation of quarks . These results can serve as a good tool to search for new physics effects, precisely, to search for the fourth generation of quarks($t', b')$ via its indirect manifestations in loop diagrams.
The rare $B\to K^{*}ν\barν$ decay when $K^{*}$ meson is longitudinally or transversely polarized is analysed in the context of the fourth generation model. A significant enhancement to the missing energy spectrum over the SM is recorded.
In this paper, we investigate the effects of the fourth generation of quarks on the double-lepton polarization asymmetries in the $B_s \rar ϕ\ell^+ \ell^-$ decay. It is shown that these asymmetries in $B_s \rar ϕ\ell^+ \ell^-$ decay compared with those of $B \rar K \ell^+ \ell^-$ decay are more sensitive to the fourth-generation parameters. We conclude that an efficient way to establish the existence of the fourth generation of quarks could be the study of these asymmetries in the $B_s \rar ϕ\ell^+ \ell^-$ decay.
Influence of the fourth generation, if ever exists, on the experimentally measurable quantities such as invariant dilepton mass distribution, lepton forward-backward asymmetry, and the ratio (Gamma_L/Gamma_T) of the decay widths when K* meson is longitudinally and transversally polarized, is studied. Using the experimental results on the branching ratios for the (B -> X_s) gamma and semileptonic (B -> X_c l nu) decays, the two possible solutions of the 4x4 Cabibbo-Kobayashi-Maskawa factor (V_{t's} V_{t^'b}) are obtained as a function of the t'-quark mass. It is observed that the results for th…
We show that the exclusive decay $B\rightarrow K^{\ast}γ$ can be related to the semileptonic decay $B\rightarrowρe\barν$ using heavy-quark symmetry and $SU(3)$ flavor symmetry. A direct measurement of the $q^{2}$-spectrum for the semileptonic decay can provide relevant information for the exclusive rare decay.
This study investigates the influence of the fourth generation quarks on the double lepton polarizations in B \rar K \ell^+ \ell^- decay. Taking |V_{t's}V_{t'b}|\sim \{0.01-0.03\} with phase about 100^\circ, which is consistent with the b\to s\ell^+\ell^- rate and the B_s mixing parameter Delta m_{B_s}$, we obtain that the double lepton(muon and tau) polarizations are quite sensitive to the existence of fourth generation. It can serve as a good tool to search for new physics effects, precisely, to indirect search for the fourth generation quarks(t', b').
The contribution of the fourth generation quarks to the rare (B_s -> l^+ l^-) and (B_s -> l^+ l^- gamma) decays are studied. Constraints on the extended Cabibbo-Kobayashi-Maskawa matrix elements |V_{tb} V_{ts}*| and |V_{t'b} V_{t's}*| are obtained from the existing experimental result for the branching ratio of the (B -> X_s gamma) decay. The branching ratios of the above-mentioned decays, as well as the photon spectrum in the (B_s -> l^+ l^- gamma) decay, are studied. It is found that the results are sensitive to the existence of the fourth generation.
We study some rare decays of $B_s$ meson governed by the quark level transitions $ b \to s$, in the fourth generation model popularly known as SM4. Recently it has been shown that SM4, which is a simple extension of the SM3, can successfully explain several anomalies observed in the CP violation parameters of $B$ and $B_s$ mesons. We find that in this model due to the additional contributions coming from the heavy $t'$ quark in the loop, the branching ratios and other observables in rare $B_s$ decays deviate significantly from their SM values. Some of these modes are within the reach of LHCb e…
This study investigates the influence of the fourth generation quarks on the total branching ratio and the single lepton polarizations in Λ_b --> Λ\ell^+ \ell^- decay. Taking $|V_{t's}V_{t'b}| {0.01-0.03} with phase just below $90^\circ$, which is consistent with the b\to s\ell^+\ell^- rate and the B_s mixing parameter Δm_{B_s}, we obtain that the total branching ratio and the single lepton(μ, τ) polarizations are quite sensitive to the existence of fourth generation. It can serve as a good tool to search for new physics effects, precisely, to search for the fourth generation quarks(t', b').
If the fourth generation fermions exist, the new quarks could influence the branching ratio of the rare $B\to K^{*}ν\barν$ decay. Two possible solutions of the fourth generation CKM factor $(V^{*}_{\acute{t}s}V_{\acute{t}b})^(\pm)$ are obtained as a function of the new $\acute{t}$-quark mass $(m_{\acute{t}})$ from the experimental results of the $B\to X_{s}γ$ together with the semileptonic decay $B\to X_{c}\ell\barν$. The branching ratio of the decay $B\to K^{*}ν\barν$ in the two cases is estimated. In one case, a significant enhancement to the branching ratio of the decay $B\to K^{*}ν\barν$ o…
In the ratio of ratios of rates for radiative and semileptonic decays of B and D to K* and rho mesons the non-computable form factors mostly cancel out. The resulting method for the determination of Vub is largely free of hadronic uncertainties, raising the prospect of a precise determination of Vub.
I review the phenomenology of exclusive Bbar -> Kbar pi l^+ l^- decays, with focus on the intermediate resonant Kbar^*(892) mode. The status of angular observables at both ends of the dilepton mass spectrum is revisited. Constraints on the b -> s Wilson coefficients C_7,C_9,C_10 based on 2011 data from the B factories, CDF and LHCb are presented.
We present an analysis on the exclusive rare radiative decay modes Sigma_b->Sigma gamma and Xi_b->Xi gamma. The transition form factors which parameterize these processes are calculated using QCD light-cone sum rules. The decay widths we predict are Gamma(Sigma_b->Sigma gamma)=(7.21\pm0.04)\times10^{-18}GeV} and Gamma(Xi_b->Xi gamma)=(1.34\pm0.07)\times10^{-16}GeV. The Branching ratio of Xi_b->Xi gamma is predicted to be Br(Ξ_b->Xi gamma)=(3.03\pm0.10)\times10^{-4}.
We report recent results in rare B decays. Our focus will be on b -> d gamma and b -> s l^+ l^- transitions. We discuss their impact on the CKM phenomenology and their role within our search for new physics. In particular, we analyse the impact of a recent lattice QCD estimate of the B -> K* form factor at zero recoil. We also briefly discuss the presently available optimal theoretical tools for the inclusive and exclusive modes.
We consider measurements of exclusive rare semi-tauonic $b$-hadron decays, mediated by the $b \rightarrow s τ^+ τ^-$ 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 $τ$ decay modes (up to discrete ambiguities). This, together with the potentially large statistics of $Z\to b\bar b$, opens the door for the experimental determination of $τ$ polarizations in these rare $b$-hadron decays. In light of the curre…
It has been shown that the data from the Large Hadron Collider (LHC) does not rule out a chiral sequential fourth generation of fermions that obtain their masses through an identical mechanism as the other three generations do. However, this is possible only if the scalar sector of the Standard Model is suitably enhanced, like embedding it in a type-II two-Higgs doublet model. In this article, we try to show that double Higgs production (DHP) can unveil the existence of such a hidden fourth generation in a very efficient way. While the DHP cross-section in the SM is quite small, it is signific…
Rare $B$-decays induced by flavour-changing neutral currents (FCNC) is one of the promising candidates for probing physics beyond the Standard model. However, for identifying potential new physics from the data, reliable control over QCD contributions is necessary. We focus on one of such QCD contributions - the charming loops - that potentially can lead to difficulties in disentangling new physics effects from the observables and discuss the possibility to gain control over theoretical predictions for charming loops.
We study the exclusive rare decay B -> K l(bar) l. We calculate the relevant form factors within a relativistic constituent quark model, for the first time without employing the impulse approximation. The calculated form factors are used to evaluate differential decay rates and polarization observables. We present results on the q2-dependence of a set of observables with and without long-distance contributions. A similar analysis is done for the exclusive rare decays B_c -> D (D*) l(bar) l with special emphasis on the cascade decay B_c -> D* (-> D pi) l(bar) l. We derive a four-fold angular de…
We present the first complete results for the semileptonic and rare radiative form factors of B-mesons weak decay into a light vector-meson (rho, omega, K*, phi) in the light-cone sum-rule approach. The calculation includes radiative corrections, higher-twist corrections and SU(3)-breaking effects. The theoretical uncertainty is investigated in detail. A simple parametrization of the form factors is given in terms of three parameters each. We find that the form factors observe several relations inspired by heavy-quark symmetry.
Rare decays $Λ_b \to Λγ$ and $Λ_b \to Λl^{+} l^{-}$ (l= e, $μ$) are examined. We use QCD sum rules to calculate the hadronic matrix elements governing the decays. The $Λ$ polarization in the decays is analyzed and it is shown that the polarization parameter in $Λ_b \to Λγ$ does not depends on the values of hadronic form factors. And the energy spectrum of $Λ$ in $Λ_b \to Λl^{+} l^{-}$ is given.
The exclusive rare radiative $B$-decays are studied in the framework of the relativistic quark model based on the quasipotential approach in quantum field theory. The large recoil momentum of the final vector meson allows for the expansion of the decay form factor in inverse powers of the b-quark mass. This considerably simplifies the analysis of these decays. The $1/m_b$ expansion is carried out up to the second order. The form factor of \btok decay is found to be $F_1^{B\to K^* γ}(0)=0.32\pm 0.03 $ and it leads to $BR(B\to K^*γ)= (4.5\pm 1.5) \times 10^{-5}$, which is in agreement with the r…
The exclusive rare decay $B \ra K^\ast γ$ takes place in a region of maximum recoil, $q^{2}=0$, posing a problem for nonrelativistic quark models which are usually thought to be most reliable at zero recoil. The Bauer--Stech--Wirbel (BSW) model, formulated in the infinite--momentum--frame (IMF) formalism, is designed to work at $q^2=0$. We show in this model that the ratio relating the decay $B \ra K^\ast γ$ and the $q^2$--spectrum of the semileptonic decay $B\ra ρe {\bar ν}$, becomes independent of the wave function in the SU(3) flavor symmetry limit. We show that this feature is also true in…
Nonperturbative effects in exclusive reactions $B\to K^{(*)}ll$ are discussed. Form factors which describe the main long-distance contribution to the meson transition amplitude are calculated within the dispersion formulation of the quark model: namely, the form factors in the decay region are expressed as relativistic double spectral representations through the wave functions of the initial and final mesons. The dilepton forward-backward asymmetry and the lepton polarization turn out to be largely independent of the particular choice of the quark model parameters and can be predicted with hig…
We study long-distance effects in rare exclusive semileptonic decays B -> (K, K*) (l+ l-, nu bar{nu}) and analyze dilepton spectra and asymmetries within the framework of the Standard Model. The form factors, describing the meson transition amplitudes of the effective Hamiltonian are calculated within the lattice-constrained dispersion quark model: the form factors are given by dispersion representations through the wave functions of the initial and final mesons, and these wave functions are chosen such that the B -> K* transition form factors agree with the lattice results at large q**2. We c…
The effects of possible right-handed weak hadronic currents in rare exclusive semileptonic decays B -> (K, K*) nu bar{nu} are investigated using a lattice-constrained dispersion quark model for the calculation of the relevant mesonic form factors. The results obtained for the branching ratios and the missing energy spectra are presented and the sensitivity of various observables to long-distance physics is investigated. It is shown that the asymmetry of transversely polarized K*(T) mesons as well as the K / K*(T) production ratio are only slightly sensitive to long-distance contributions and m…
In these lectures we give, first, the model-independent analysis of the exclusive rare decays B -> K l(bar) l and B_c -> D(D*) l(bar) l with special emphasis on the cascade decay B_c -> D(*)(-> D pi) l(bar) l. We derive a four-fold angular decay distribution for this process in terms of helicity amplitudes including lepton mass effects. The four-fold angular decay distribution allows to define a number of physical observables which are amenable to measurement. Second, we calculate the relevant form factors within a relativistic constituent quark model, for the first time without employing the …
The large cross section for t-tbar production at the LHC and at any future hadron collider provides a high-statistics and relatively clean environment for a study of W boson properties: after tagging on a leptonic decay of one of the Ws and the two b-jets, an additional W still remains in the event. We study the prospect of making the first exclusive hadronic decay of a fundamental boson of the standard model, using the decay modes W to pi gamma and W to pi pi pi, and other related decays. By using strong isolation criteria, which we impose by searching for jets with a single particle constitu…
We present a model-independent description of the exclusive rare decays B-> K* e+e- in the low recoil region (large lepton invariant mass q^2 ~ m_b^2). In this region the long-distance effects from quark loops can be computed with the help of an operator product expansion in 1/Q, with Q={m_b, \sqrt{q^2}}. Nonperturbative effects up to and including terms suppressed by Lambda/Q and mc^2/mb^2 relative to the short-distance amplitude can be included in a model-independent way. Based on these results, we propose an improved method for determining the CKM matrix element |V{ub}| from a combination o…
B meson rare decays ($B\to K(K^{*})l\bar l$ and $B\to K^*γ$) are analyzed in the framework of effective field theory of heavy quarks. The semileptonic and penguin type form factors for these decays are calculated by using the light cone sum rules method at the leading order of $1/m_Q$ expansion. Four exact relations between the two types of form factors are obtained at the leading order of $1/m_Q$ expansion. Of particular, the relations are found to hold for whole momentum transfer region. We also investigate the validity of the relations resulted from the large energy effective theory based o…
We study the light-front zero-mode contribution to the tensor form factors $T_i(i=1,2,3)$ for the exclusive rare $P\to V\ell^+\ell^-$ decays using a covariant fermion field theory model in $(3+1)$ dimensions. While the zero-mode contribution in principle depends on the form of the vector meson vertex $Γ^μ=γ^μ- (2k-P_V)^μ/D$, the three tensor form factors $T_i(i=1,2,3)$ are found to be free from the zero mode if the denominator $D$ contains the term proportional to the light-front energy or the longitudinal momentum fraction factor $(1/x)^n$ of the struck quark with the power $n>0$. Since the d…
The invariant mass spectrum, forward-backward asymmetry, and lepton polarizations of the exclusive processes $B\to K(K^*)\ell^+ \ell^-, \ell=μ, τ$ are analyzed under supersymmetric context. Special attention is paid to the effects of neutral Higgs bosons (NHBs). Our analysis shows that the branching ratio of the process $\bkm$ can be quite largely modified by the effects of neutral Higgs bosons and the forward-backward asymmetry would not vanish. For the process $\bksm$, the lepton transverse polarization is quite sensitive to the effects of NHBs, while the invariant mass spectrum, forward-bac…
We consider rare radiative B decays such as B -> K^* gamma or B -> rho gamma in soft-collinear effective theory, and show that the decay amplitudes are factorized to all orders in alpha_s and at leading order in Lambda/m_b.By employing two-step matching, we classify the operators for radiative B decays in powers of a small parameter lambda(~ \sqrt{Lambda/m_b}) and obtain the relevant operators to order lambda in SCET_I. These operators are constructed with or without spectator quarks including the four-quark operators contributing to annihilation and W-exchange channels. And we employ SCET_II …
We evaluate the LHC's potential of observing Higgs boson decays into light elementary or composite resonances through their hadronic decay channels. We focus on the Higgs boson production processes with the largest cross sections, $pp\to h$ and $pp\to h+\mathrm{jet}$, with subsequent decays $h \to ZA$ or $h\to Z\,η_c$, and comment on the production process $pp\to hZ$. By exploiting track-based jet substructure observables and extrapolating to $3000~\mathrm{fb}^{-1}$ we find ${\cal BR}(h \to ZA) \simeq {\cal BR}(h \to Z η_c) \lesssim 0.02$ at 95% CL. We interpret this limit in terms of the 2HDM…
In this study a systematical analysis of various polarization asymmetries in inclusive $b \rar s \ell^+ \ell^-$ decay in the standard model (SM) with four generation of quarks is carried out. We found that the various asymmetries are sensitive to the new mixing and quark masses for both of the $μ$ and $τ$ channels. Sizeable deviations from the SM values are obtained. Hence, $b \rar s \ell^+ \ell^-$ decay is a valuable tool for searching physics beyond the SM, especially in the indirect searches for the fourth-generation of quarks ($t', b')$.
This review discusses the present experimental and theoretical status of rare flavour-changing neutral current $b$-quark decays at the begin of 2018. It includes a discussion of the experimental situation and details of the currently observed anomalies in measurements of flavour observables, including lepton flavour universality. Progress on the theory side, within and beyond the Standard Model theory is also discussed, together with potential New Physics interpretations of the present measurements.
We investigate the $ε^{\prime} /ε$ for $K\to ππ$ in a sequential fourth generation model. By giving the basic formulae for $ε^{\prime}/ε$ in this model, we analyze the numerical results which are dependent of $m_{t^{\prime}}$ and imaginary part of the fourth CKM factor, ${Im}V^{*}_{t^{'}s}V_{t^{'}d}$ (or $V^{*}_{t^{'}s}V_{t^{'}d}$ and the fourth generation CKM matrix phase $θ$). We find that, unlike the SM, when taking the central values of all parameters for $ε^{\prime}/ε$, the values of $ε^{\prime}/ ε$ can easily fit to the current experimental data for all values of hadronic matrix elements…
For a model with a fourth family of quarks, new sources of flavor changing neutral currents are identified by confronting the unitary 4x4 quark mixing matrix with the experimental measured values of the familiar 3x3 quark mixing matrix. By imposing as experimental constraints the known bounds for the flavor changing neutral currents, the largest mixing of the known quarks with the fourth family ones is established. The predictions are: a value for |V_{tb}| significantly different from unity, large rates for rare top decays as t->cγand t->cZ, the last one reachable at the Large Hadrion Collider…
We review our works on the sequential fourth generation model and focus on the constriants of $4\times 4$ quark mixing matrix elements. We investigate the quark mixing matrix elements from the rare $K,B$ meson decays. We talk about the $ hierarchy$ of the $4\times 4$ matrix and the existence of fourth generation.
This study examines the influence of the fourth generation quarks on the double lepton polarizations forward--backward asymmetries in B \rar K^\ast \ell^+ \ell^- decay. We obtain that for both (muon, tau) channels the magnitude and the sign of the differential forward--backward asymmetries and the magnitude of the average forward--backward asymmetries are quite sensitive to the 4th generation quarks mass and mixing parameters. It can serve as a good tool to search for new physics effects, precisely, to search for the fourth generation quarks(t', b') via its indirect manifestations in the loop …
The rare decays of $Λ_b$ baryon governed by the quark level transitions $ b \to s$, are investigated in the fourth quark generation model popularly known as SM4. Recently it has been shown that SM4, which is a very simple extension of the standard model, can successfully explain several anomalies observed in the CP violation parameters of $B$ and $B_s$ mesons. We find that in this model due to the additional contributions coming from the heavy $t'$ quark in the loop, the branching ratios and other observables in rare $Λ_b$ decays deviate significantly from their SM values. Some of these modes …
We use loop induced processes like meson oscillations and rare b hadron decays to determine the absolute values of the CKM matrix elements $|V_{ub}|$ and $|V_{cb}|$ and compare our results to the standard determinations based on inclusive and exclusive semileptonic tree-level decays of B mesons. For many years there have been tensions between the inclusive and exclusive determinations. Assuming the absence of new physics, we find that meson oscillation data shows a slight preference for the inclusive value of $|V_{cb}|$ and the exclusive value for $|V_{ub}|$. Rare b decay data prefers values f…
The realization that first- and second-generation Yukawa couplings can be probed by decays of the Higgs boson to a meson in association with a photon has renewed interest in such rare exclusive decays. We present here a detailed study of the rare $Z$-boson processes $Z \to J/ψ+γ$, $Z \to Υ+γ$, and $Z \to ϕ+γ$ that can serve as benchmarks for the analogous Higgs-boson decays. We include both direct-production and fragmentation contributions to these decays, and consider the leading QCD corrections and the relativistic corrections to the $J/ψ$ and $Υ$ processes. We present numerical predictions …
In the SUSY SO(10) GUT context, we study the exclusive processes $B \to K^{(*)} l^+l^-(l=μ,τ)$. Using the Wilson coefficients of relevant operators including the new operators $Q_{1,2}^{(\prime)}$ which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like, the invariant mass spectrum (IMS), lepton pair forward backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients $C_{Q_{1,2}}^\prime$, among new contributions, are dominant. Our results show that the NHB effe…
Efforts to predict the rare exclusive decay $B\to K^{\ast}γ$ from the well known inclusive decay $b\to sγ$ are frustrated by the effect of the large recoil momentum. We show how to reduce the large uncertainty in calculating this decay by relating $B\to K^{\ast}γ$ to the semileptonic process $B\toρe\barν$ using the heavy-quark symmetry in B decays and SU(3) flavor symmetry. A direct measurement of the $q^{2}$-spectrum for the semileptonic decay can provide accurate information for the exclusive rare decay.
We revisit four generations within the context of supersymmetry. We compute the perturbativity limits for the fourth generation Yukawa couplings and show that if the masses of the fourth generation lie within reasonable limits of their present experimental lower bounds, it is possible to have perturbativity only up to scales around 1000 TeV, i.e. the current experimental bounds and perturbative unification are mutually exclusive. Such low scales are ideally suited to incorporate gauge mediated supersymmetry breaking, where the mediation scale can be as low as 10-20 TeV. The minimal messenger m…
Using the QCD {\it hybrid} (moments-Laplace) sum rule, we show $semi$-$analytically$ that, in the limit $M_b \rar \infty$, the $q^2$ and $M_b$ behaviours of the heavy-to-light exclusive ($\bar B\rar ρ~(π)$ semileptonic as well as the $ B\rar ργ$ rare) decay--form factors are $universally$ dominated by the contribution of the soft light-quark condensate rather than that of the hard perturbative diagram. The QCD-analytic $q^2$ behaviour of the form factors is a polynomial in $q^2/M^2_b$, which mimics quite well the usual pole parametrization, except in the case of the $A_1^B$ form factor, where …
We have investigated $B \to (K,K^*)(l\bar l,ν\barν)$ decay channels and predicted some form factor dependent observables (e.g. branching ratio, forward-backward asymmetry and lepton polarization asymmetry) considering new physics contribution from non-universal $Z'$ model. We have found that there is appreciable difference between the standard model and $Z'$ model predictions. Recently, the lepton flavour non-universality parameters $R_K$ and $R_{K^*}$ have been measured by the LHCb collaboration and are found to be different from their standard model predictions. These deviations provide the …
Exclusive rare Higgs decays into lepton pair plus one light hadron, such as $h\to ρ^0(ω)\ell\bar{\ell}$, $h\to π^0\ell\bar{\ell}$, $h\to π^+ (K^+)\ell^-\barν_\ell$, and $h\to ρ^+(K^{*+})\ell^-\barν_\ell$, have been explored in the standard model. Decay amplitudes are dominantly from the Higgs couplings to gauge bosons and to charged leptons, and their branching ratios are predicted in the range of $10^{-8}\sim 10^{-5}$. We have also analyzed the differential dilepton invariant mass and angular distributions of $h\to ρ^0 \ell^+\ell^-$ decays. It will be challenging to search for these rare proc…
We calculate the independent helicity amplitudes in the decays $B \to K^* \ell^+ \ell^-$ and $B \to ρ\ell ν_\ell$ in the so-called Large-Energy-Effective-Theory (LEET). Taking into account the dominant $O(α_s)$ and SU(3) symmetry-breaking effects, we calculate various Dalitz distributions in these decays making use of the presently available data and decay form factors calculated in the QCD sum rule approach. Differential decay rates in the dilepton invariant mass and the Forward-Backward asymmetry in $B \to K^* \ell^+ \ell^-$ are worked out. We also present the decay amplitudes in the transve…
We use the new symmetries in the heavy quark limit to calculate the exclusive B-decays $B \rightarrow K ψ(ψ^{\prime})$ and $B \rightarrow K^* ψ(ψ^{\prime})$. The estimated decay rates are compared with experimental values. We also estimate rare $B \rightarrow K^* γ$ decay rate, based on these experimental data and heavy quark symmetry.
We investigate the exclusive rare $B_c\to D_{(s)}ν_{\ell}\bar{ν_{\ell}}$ and $B\to D_{(s)}\ell^+\ell^-$ ($\ell=e,μ,τ$) decays within the standard model and the light-front quark model constrained by the variational principle for the QCD motivated effective Hamiltonian. The form factors $f_{\pm}(q^2)$ and $f_T(q^2)$ are obtained from the analytic continuation method in the $q^+=0$ frame. While the form factors $f_+(q^2)$ and $f_T(q^2)$ are free from the zero-mode, the form factor $f_-(q^2)$ is not free from the zero-mode in the $q^+=0$ frame. We discuss the covariance(i.e. frame-independence) o…
A model-independent analysis for the exclusive, rare B -> pi^+ pi^- l^+ l^- decay is presented. The dependence of the various physically measurable asymmetries and CP violating asymmetry on the new Wilson coefficients is studied in detail. It is observed that different measurable quantiles are very sensitive to the different new Wilson coefficients, i.e., to the existence of new physics beyond standard model.
Using the most general, model-independent form of effective Hamiltonian, the exclusive, rare $B \rar K^\ast ν\bar ν$ decay is analyzed. The sensitivity of the branching ratios and missing mass-squared spectrum to the new Wilson coefficients is discussed.
Using the light-front quark model, we calculate the transition form factors, decay rates, and longitudinal lepton polarization asymmetries for the exclusive rare $B_s\to (K,η^{(\prime)})(\ell^+\ell^-,ν_{\ell}\bar{ν_{\ell}}$ ($\ell=e,μ,τ$) decays within the standard model, taking into account the $η-η'$ mixing angle. For the mixing angle $θ=-20^{\circ}$ ($-10^{\circ}$) in the octet-singlet basis, we obtain ${\rm BR}(B_s\to η\sumν_{\ell}\barν_{\ell})=1.1 (1.7)\times 10^{-6}$, ${\rm BR}(B_s\to ημ^+μ^-)=1.5 (2.4)\times 10^{-7}$, ${\rm BR}(B_s\to ητ^+τ^-)=3.8 (5.8)\times 10^{-8}$, ${\rm BR}(B_s\to …
Rare Lambda_b -> Lambda l^+ l^- decay is investigated in framework of general two Higgs doublet model, in which a new source of CP violation exists (model III). The polarization parameter, CP asymmetry and decay width are calculated. It is shown that CP asymmetry is a very sensitive tool for establishing model III.
