Improved analysis of the rare decay processes of Λ_b

It is noted that in the new Particle Data Group(PDG) version the rare decays of the Λ_b baryon have been revised with more accuracy. The new results show that most of the existing theoretical results on the process Λ_b→Λ_γ Lgbare larger than those of experiments. With the improved higher-order light-cone distribution amplitudes of the Λ baryon, we reanalyze the process in the framework of light-cone quantum chromodynamics sum rules and the branching ratio is estimated to be Br (Λ_b→Λ_γ)=(7.38_(-0.39)~(+0.40))×10~(16), which is consistent with the new experimental result. Furthermore, another process Λ_b→Λl~+l~- is also analyzed in the same frame. The final branching ratio is calculated to be Br (Λ_b→Λl~+l~-)=1.20×10~(-6), which is in good accordance with the data from the PDG and other theoretical predictions.     

Exclusive Semi-leptonic Decays b → s(d)ν in the Standard Model with Fourth Generation

We consider the effects of the fourth generation quarks on the rare B decay processes described by the b → s(d)ννˉ processes at the quark level.We find that the values of the branching ratios for some of these rare decay processes are much larger than the standard model(SM) predictions.These processes can be used to constrain the relevant free parameters.     

Impacts of the Soft—Gluon Exchanges on B→ππ Decays

We have investigated the role of soft-gluon exchanges in B→ππ,using the light-cone sum rules in quantum chromodynamics,The calculations are carried out not only for the tree operators but also for the penguin operators.We conclude that soft-gluon exchanges contribute to the decay amplitudes,noticeably on some decay channels,and thus cannot be neglected.     

B → A transitions in the light-cone QCD sum rules with the chiral current

In this article, we calculate the form-factors of the transitions B → a₁(1260), b₁(1235) in the leading-order approximation using the light-cone QCD sum rules. In calculations, we choose the chiral current to interpolate the B-meson, which has the outstanding advantage that the twist-3 light-cone distribution amplitudes of the axial-vector mesons makes no contributions, and the resulting sum rules for the form-factors suffer from far fewer uncertainties. Then we study the semi-leptonic decays B → a₁(1260) lv_l, b₁(1235) lv_l (l=e,μ,τ), and make predictions for the differential decay widths and decay widths, which can be compared with the experimental data in the coming future.     

Semileptonic bc to cc and bb to bc baryon decays and heavy quark spin symmetry

We study the semileptonic decays of the lowest-lying bc baryons to the lowest-lying cc baryons (Ξ (*) bc →Ξ (*) cc and Ω ( *) bc →Ω (*) cc ),in the limit m b,m c Λ QCD and close to the zero recoil point.The separate heavy quark spin symmetries make it possible to describe all these decays using a single form factor.We also show how these constraints can be used to test the validity of different quark model calculations.bb to bc baryon decays are also discussed.     

B-Meson Wavefunction by a Comparative Analysis of the B → π, K Transition Form Factors

Properties of the B-meson light-cone wavefunction up to next-to-leading order Fock state expansion are studied by a comparative study of the B → π, K form factors within the kT factorization approach and the light-cone sum rule analysis. The form factors F＋,0,T^B→ π and F＋,0,T^B→ K are carefully re-calculated up to O（1/mb^2） within the kT factorization approach in the large recoil region. The QCD light-cone sum rule is applicable in the large and intermediate energy regions, and the QCD light-cone sum rule results in Ref. [12] are adopted for such a comparative study. It is found that when the two phenomenological parameters ∧^-∈ [0.50, 0.55] and δ∈ [0.25, 0.30], the results of F＋,0,T^B→ π （Q^2 ） and F＋,0,T^B→ K（Q ^2） from these two approaches are consistent with each other in the large recoil energy region.     

Analysis of Λ_b →Λl~+l~- rare decays in a non-universal Z’ model

We investigate the rare baryonic Λ_b→Λl~+l~- decays in a non-universal Z’ model, which is one of the wellmotivated extensions of the standard model(SM). Considering the effects of Z-mediated flavour-changing neutral currents(FCNCs) we analyse the differential decay rate, forward-backward asymmetries and lepton polarisation asymmetries for the Λ_b→Λl~+l~- decays. We find significant deviations from their SM predictions, which could indicate new physics arising from the Z gauge boson.     

Electromagnetic properties of the Pc(4312) pentaquark state

Using the light-cone QCD sum rules,we evaluate the magnetic moment of the P_c(4312) pentaquark state by considering both the \bar D\Sigma_c molecular and diquark-diquark-antiquark state,with quantum numbers J^P=2/1^-1.In the calculations,we use the diquark-diquark-antiquark and molecular form of the interpolating currents for the P_c4312 pentaquark and the distribution amplitudes of the photon.The numerical results for the magnetic moment obtained using the two different pictures are quite different from each other,which can be used to pin down the underlying structure of P_c4312 .Any experimental measurement of the magnetic moment in the near future will provide an understanding of the internal structure of this pentaquark state.     

Exclusive Semileptonic Rare Decays B → K^（＊）e＋e- in a Top Quark Two-Higgs-Doublet Model

Employing improved calculations of the decay form factors from light-cone sum rules, we evaluate the invariant mass spectrum, forward-backward asymmetry, and lepton polarizations of the exclusive processes B → K^（＊）e＋e- in the SM and T2HDM. From the recent measurements of their branching ratios, we find that these processes do provide additional bounds on the new parameters in the model considered here. After the inclusion of the new physics contributions, the large enhancement of FBA, which is unobservably small within the SM and of the lepton polarization at large tan β, may precisely test the SM or reveal new physics in forthcoming accurate experiments.     

Semileptonic bc to cc and bb to bc baryon decays and heavy quark spin symmetry

We study the semileptonic decays of the lowest-lying bc baryons to the lowest-lying cc baryons （Ξ （＊） bc → Ξ （＊） cc and Ω （ ＊） bc → Ω （＊） cc ）,in the limit m b,m c Λ QCD and close to the zero recoil point.The separate heavy quark spin symmetries make it possible to describe all these decays using a single form factor.We also show how these constraints can be used to test the validity of different quark model calculations.bb to bc baryon decays are also discussed.     

Rare Decay Process K→πvv^- in Three-Site Higgsless Model]

Rare decay processes K→πvv^- and KL→π^0vv^- are considered in the framework of three-site Higgsless model. The contributions of this new physics model to these two decay processes come from the new heavy gauge bosons and the correction terms for the couplings of the ordinary gauge bosons with fermions. Our numerical results show that the branching ratios of these two decay processes can be enhanced by 40% and 50% relative to those predicted by the standard model.     

Top rare decays t→cV in mirror twin Higgs models

The decay t→cV(V=γ,Z,g)processes in mirror twin Higgs models with colorless top partners are studied in this paper.We report that the branchi ng ratios of these decays can strongly affect the standard model expectations in some parameter spaces and may be detectable according to the current precision electroweak measurements.Thus,constraints on the model parameters may be obtained from the branching fraction of the decay processes,which may serve as a robust detection tool for this new physics model.     

Helicity Amplitude Analysis of e^＋e^- ψ（2S） → γχcJ→γ∧∧^-→γpπ^-p^-π^＋＊

An analysis of the helicity amplitude is performed on the process e^＋e^- ψ（2S） → γχcJ→γ∧∧^-→γpπ^-p^-π^＋. The joint angular distributions for each decay chain are given, and we focus on discussing the E1 contributions to ψ（2S） radiative decays, and the violation of the helicity selection rule in χcJ decays into hyperon pairs, together with the possibility of observing parity violation in successive hyperon decays.     

Study of the s → dv■ rare hyperon decays in the Standard Model and new physics

FCNC processes offer important tools to test the Standard Model(SM)and to search for possible new physics.In this work,we investigate the s→dvv rare hyperon decays in SM and beyond.We find that in SM the branching ratios for these rare hyperon decays range from 10~(-14) to 10~(-11).When all the errors in the form factors are included,we find that the final branching ratios for most decay modes have an uncertainty of about 5% to 10%.After taking into account the contribution from new physics,the generalized SUSY extension of SM and the minimal 331 model,the decay widths for these channels can be enhanced by a factor of 2～7.     

Dynamically generated resonances from the vector octet-baryon decuplet interaction and their radiative decays into $\gamma$-baryon decuplet

The dynarnically generated resonances from vector meson-baryon decuplet are studied using La- grangians of the hidden gauge theory for vector interactions. One shows that some of the generated states can be associated with some known baryon resonances in the PDG data, while others are predictions for new states. Furthermore, we calculate the radiative decay widths of these resonances into a photon and a baryon decuplet.     

Searching for Flavor-Changing Neutral-Current Signals via e＋e-（γγ） →tcht0 in Topcolor-Assisted Technicolor Model

In the context of the top-color-assisted technicolor （TC2） model, the flavor-changing neutral-current （FCNC） interaction induced by the top-higgs （hOt） are predicted at tree level. We study the relevant processes of e＋e-（γγ）→tcht0 at the International Linear Collider （ILC）. It is found that these rare processes production rates can be enhanced significantly in the TC2 model. Especially for the process γγ→tcht0, the total cross section will reach a few fb in the reasonable parameter space. We also calculate the distributions of transverse momenta, pseudo-rapid and invariant mass of the top-higgs. In view of the main decay modes of top-higgs for mho 〈 2mr, we find that there will be several hundreds FCNC events produced at the ILC with annually integral luminosity of 500 fb-1. Due to the clean background, such FCNC signals can possibly be detected at the ILC.     

B→K Transition Form Factor with Tensor Current within the kT Factorization Approach

We apply the kT factorization approach to deal with the B→K transition form factor with tensor current in the large recoil regions. Main uncertainties for the estimation are discussed and we obtain FT^B→K （0） = 0.25±0.01±0.02, where the first error is caused by the uncertainties from the pionic wavefunctions and the second is from that of the B-meson wavefunctions. This result is consistent with the light-cone sum rule results obtained in the literature.     

Implications of the RK and R_(K*) anomalies

We discuss the implications of the recently reported R_K and R_(K*) anomalies, the lepton flavor nonuniversality in the B → Kl~+l~-and B → K~*l~+~l- decay channels. Using two sets of hadronic inputs of form factors, we perform a fit of new physics to the R_K and R_(K*) data, and significant new physics contributions are found. We suggest the study of lepton flavor universality in a number of related rare B,Bs,Bc and Λb decay channels, and in particular we give predictions for the μ-to-e ratios of decay widths with different polarizations of the final state particles, and of the b → dl~+l~- processes, which are presumably more sensitive to the structure of the underlying new physics. With the new physics contributions embedded in the Wilson coefficients, we present theoretical predictions for lepton flavor non-universality in these processes.     

B → X_sγ in BLMSSM

Applying the effective Lagrangian method,we study the flavor changing neutral current process b→ sγwithin the minimal supersymmetric extension of the Standard Model,where baryon and lepton numbers are local gauge symmetries.Constraints on the parameters are investigated numerically with the experimental data for the branching ratio of B→ X_sγ.Additionally,we present the corrections to direct CP-violation in B→ X_sγ and time-dependent CP-asymmetry in B→K~*γ.With appropriate assumptions on the parameters,we find the direct CP-violation Acp is very small,while one-loop contributions to S_(K~*_γ) can be significant.     

A family of double-beauty tetraquarks:Axial-vector state T-bb;(us)

The spectroscopic parameters and decay channels of the axial-vector tetraquark Tho(in what follows,TAV)are explored using the quantum chromodynamics(QCD)sum rule method.The mass and coupling of this state are calculated using two-point sum rules by taking into account various vacuum condensates,up to 10 dimensions.Our prediction for the mass of this state m=(10215±250)MeV confirms that it is stable with respect to strong and electromagnetic decays and can dissociate to conventional mesons only via weak transformations.We investigate the dominant semileptonic■and nonleptonic T AV b:s^-→v10 b:s^-M decays of T AV b:s^-.In these processes,Z-b:s^-is a scalar tetraquark[be][us^-]built of a colo-triplet diquark and an antidiquark,whereas M is one of the vector mesonsρ^-,K^*(892),D^*(2010)^-,and D^*s-.To caleulate the partial w idths of these decays,we use the QCD three-point sum rule approach and evaluate the weak transition form factors Gi(i=0,1,2,3),which govem these processes.The full widthΓfull=(12.9±2.1)×10^-8 MeV and the mean lifetimeτ=5.1+0.99-0.71 fs of the tetraquark TAV are computed us-ing the aforementioned weak decays.The obtained information about the parametersof TAY and Zh,is useful for experimental investigations of these double-heavy exotic mesons.