Search

The semitauonic $B_c^- \to J/ψτ^-\barν_τ$ decay is optimal to scrutinize possible new physics effects in $b \to c τ^- \barν_τ$ transitions as indicated by the current data on $R(D^{(*)})$ anomalies. In this work, we study the $B_c^- \to J/ψτ^-\barν_τ$ decay with both polarized $τ$ and $J/ψ$. Their subsequent decays, with $J/ψ\to μ^+ μ^-$ as well as $τ^- \to π^- ν_τ$, $τ^- \to ρ^- ν_τ$ and $τ^- \to \ell^-\barν_\ellν_τ$, are exploited to extract the energy and angular distributions of the charged final-state particles in the processes. Starting with the most general effective Hamiltonian relevant for the $b \to c τ^- \barν_τ$ transitions, including all possible Lorentz structures of the dimension-six operators with both left- and right-handed neutrinos, we first derive the five-fold differential decay rate in terms of the visible final-state kinematics. From this distribution, we then construct in total 34 normalized observables, among which nine refer to the CP-violating triple product asymmetries that vanish within the Standard Model. We also construct five new observables based on the combinations of these normalized observables that can only be attributed to the right-handed neutrinos. On the other hand, considering the low statistics of the fully differential distribution, we introduce some integrated observables with only one kinematic variable left, which are more promising to be measured due to the largely increased statistics. The sensitivities of all these observables to the different new physics scenarios are investigated in detail. Finally, assuming an ideal circumstance, we give an estimate of the statistical uncertainties of the nine CP-conserving observables at LHCb and found that $τ^-\to π^-ν_τ$ has the highest analyzing power among the three $τ$ decay channels., 40 pages, 7 figures and 2 tables; SM predictions in different q2 bins added, final version published in the journal

Motivated by the latest CDF $W$-mass measurement as well as the muon $g-2$ anomaly and the discrepancies observed in $b \to s \ell^+ \ell^-$ transitions, we propose an extension of the Standard Model (SM) with the $SU(2)_L$-singlet vector-like fermion partners that are featured by additional $U(1)^\prime$ gauge symmetry. The fermion partners have the same SM quantum numbers as of the right-handed SM fermions, and can therefore mix with the latter after the electroweak and the $U(1)^\prime$ symmetry breaking. As a result, desirable loop-level corrections to the $(g-2)_\mu$, the $W$-boson mass $m_W$ and the Wilson coefficient $C_9$ in $b \to s \mu^+ \mu^-$ transitions can be obtained. The final allowed parameter space is also consistent with the constraints from the $Z \to \mu^+ \mu^-$ decay, the neutrino trident production and the LHC direct searches for the vector-like quarks and leptons., Comment: 34 pages, 15 figures, comments welcome

The absence of semitauonic decays of charmed hadrons makes the decay processes mediated by the quark-level $c\to d τ^+ ν_τ$ transition inadequate for probing a generic new physics (NP) with all kinds of Dirac structures. To fill in this gap, we consider in this paper the quasielastic neutrino scattering process $ν_τ+n\to τ^-+Λ_c$, and propose searching for NP through the polarizations of the $τ$ lepton and the $Λ_c$ baryon. In the framework of a general low-energy effective Lagrangian, we perform a comprehensive analysis of the (differential) cross sections and polarization vectors of the process both within the Standard Model and in various NP scenarios, and scrutinize possible NP signals. We also explore the influence on our findings due to the uncertainties and the different parametrizations of the $Λ_c \to N$ transition form factors, and show that they have become one of the major challenges to further constrain possible NP through the quasielastic scattering process., 31 pages, 17 figures, and 3 tables. Comments are welcome

If the leptoquarks proposed to account for the intriguing anomalies observed in the $B$-meson decays, $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$, as well as in the anomalous magnetic moment of the muon, $(g-2)_\mu$, can be embedded into the scotogenic Dirac neutrino model, all these flavor anomalies, together with the origin of neutrino masses and the nature of dark matter, would be potentially addressed in a unified picture. Among the minimal seesaw, one-loop, and two-loop realizations of the dimension-4 effective operator $\mathcal{L}_{4}$ for the Dirac neutrino masses, we show that plenty of diagrams associated with the two-loop realizations of $\mathcal{L}_{4}$ can support the coexistence of leptoquarks and dark matter candidates. After a simple match of these leptoquarks to those that can accommodate all the flavor anomalies, we establish the scotogenic Dirac neutrino models embedded with leptoquarks, which could address all the problems mentioned above., Comment: 15 pages, 16 tables, 9 figures

If the Dirac neutrino masses are generated by a new scalar doublet with a vacuum at keV order, there would be rare hope to probe the framework in low-energy flavor physics, such as the lepton-flavor violating processes. However, the predicted neutrino Yukawa couplings being around the order of electronic Yukawa can realize a purely thermal Dirac leptogenesis, and thus render a more direct link between the high- and the low-energy CP violation. Despite its inert property in the low-energy flavor processes, the keV-vacuum induced Dirac neutrino model can generate a significant shift of the effective neutrino number, which can in turn be probed by the big-bang nucleosynthesis and cosmic microwave background epochs. We show that such a keV-vacuum induced Dirac neutrino model is already constrained by the current observations and will be probed with forecast sensitivity, serving therefore as a complementary avenue to test the Dirac leptogenesis., 8 pages, and 3 figures

We update the Standard Model (SM) predictions for the branching ratios of the rare top-quark decays $t \to cg(g)$, and evaluate the maximum rates that can be reached in the aligned as well as in the four conventional two-Higgs-doublet models (2HDMs) with $\mathcal{Z}_2$ symmetries. Taking into account the relevant constraints on the model parameters resulting from a global fit obtained at the $95.5\%$ confidence level, we find that the branching ratios of $t \to cg$ and $t \to cgg$ decays can reach up to $3.36\times 10^{-9}$ and $2.95\times 10^{-9}$ respectively, being therefore of the same order, in the aligned 2HDM (A2HDM). This is obviously different from the SM case, where the predicted branching ratio of the three-body decay $t \to cgg$ is about two orders of magnitude larger than that of the two-body decay $t \to cg$. On the other hand, compared with the SM predictions, no significant enhancements are observed in the four conventional 2HDMs with $\mathcal{Z}_2$ symmetries for the branching ratios of these two decays. Nevertheless, the predicted branching ratios of $t \to cg$ and $t \to cgg$ decays in the A2HDM are still out of the expected sensitivities of the future high-luminosity Large Hadron Collider and the Future Circular Collider in hadron-hadron mode., 48 pages, 6 figures, and 4 tables; more references and discussions added, final version published in the journal

We investigate the potential for searching and identifying the leptoquark (LQ) effects in the charm sector through the low-energy polarized scattering processes $\vec{e}^{\,-}p\to e^-Λ_c$, $e^-\vec{p}\to e^-Λ_c$, and $\vec{e}^{\,-}\vec{p}\to e^-Λ_c$. Considering only the longitudinally polarized processes, we show that the different LQ models can be disentangled from each other by measuring the four spin asymmetries, $A_{L}^e$, $A_{L}^p$, $A_{L3}^{ep}$, and $A_{L6}^{ep}$, constructed in terms of the polarized cross sections. Although it is challenging to accomplish the same goal with transversely polarized processes, we find that investing them in future experiments is especially beneficial, since they can directly probe into the imaginary part of the Wilson coefficients in the general low-energy effective Lagrangian. With our properly designed experimental setups, it is also demonstrated that promising event rates can be expected for all these processes and, even in the worst-case scenario -- no LQ signals are observed at all, they can still provide a competitive potential for constraining the new physics, compared with those from the conventional charmed-hadron weak decays and the high-$p_T$ dilepton invariant mass tails at high-energy colliders., 24 pages, 11 tables, and 7 figures; more discussions and references added, final version published in the journal

The recently updated measurement of the $W$-boson mass by the CDF collaboration exhibits a $7\sigma$ deviation from the SM expectation, which may imply a sign of new physics beyond the SM. The observed discrepancy could be explained by new fermions that carry the electroweak gauge charges and affect the vacuum polarization of gauge bosons. Notably, if the new fermions also have the same quantum numbers as of the SM quarks, they can mix with the latter and thus modify the penguin diagrams governing the $b \to s \ell^+ \ell^-$ transitions. Therefore, the $W$-boson mass shift could be related to the $b \to s \ell^+ \ell^-$ anomalies observed by the LHCb collaboration during the past few years. To investigate this possibility, we consider in this paper a model containing a vector-like top partner gauged under a new $U(1)^\prime$ symmetry. It is found that the latest CDF $m_W$ measurement and the $b \to s \ell^+ \ell^-$ anomalies can be simultaneously accommodated at $2\sigma$ level., Comment: 7 pages, 3 figures, typos fixed, figures refined, and references added

Motivated by the recent anomalies in $b \to s \ell^+ \ell^-$ transitions, we explore a minimal $Z^\prime$ scenario, in which the $Z^\prime$ boson has a flavour-changing coupling to charm and top quarks and a flavour-conserving coupling to muons. It is found that such a $Z^\prime$ boson can explain the current $b \to s \ell^+ \ell^-$ anomalies, while satisfying other flavour and collider constraints simultaneously. The $Z^\prime$ boson can be as light as few hundreds GeV. In this case, the $t \to c \mu^+ \mu^-$ decay and the $tZ^\prime$ associated production at the LHC could provide sensitive probes of such a $Z^\prime$ boson. As a special feature, the $Z^\prime$ contributions to all rare $B$- and $K$-meson processes are controlled by one parameter. This results in interesting correlations among these processes, which could provide further insights into this scenario. In addition, an extended scenario, in which the $Z^\prime$ boson interacts with the $SU(2)_L$ fermion doublets with analogous couplings as in the minimal scenario, is also investigated., Comment: 40 pages, 13 figures, typos fixed, comments and references added

The updated measurements from the LHCb and SH0ES collaborations have respectively strengthened the deviations of the ratio $R_{K}$ in rare semi-leptonic $B$-meson decays and the present-day Hubble parameter $H_0$ in the Universe, implying tantalizing hints of new physics beyond the Standard Model. In this paper, we consider a simple flavor-specific two-Higgs-doublet model, where the long-standing $R_{K^{(*)}}$ anomalies can be addressed by a one-flavor right-handed neutrino. One of the intriguing predictions resulting from the parameter space for the $R_{K^{(*)}}$ resolution under flavor- and collider-physics constraints points toward a shift of the effective neutrino number, $\Delta N_{\rm eff}=N_{\rm eff}-N_{\rm eff}^{\rm SM}$, as favored to ease the $H_0$ tension. Depending on whether the neutrino is of Dirac or of Majorana type, we show that the resulting shift is $\Delta N_{\rm eff}\simeq 1.0$ for the former and $\Delta N_{\rm eff}\simeq 0.5$ for the latter case, respectively. While the Dirac case is disfavored by the CMB polarization measurements, the Majorana solution is consistent with the recent studies via a combined data set from various sources. Consequently, such a simple flavor-specific two-Higgs-doublet model provides a link between the $R_{K^{(*)}}$ anomalies and the $H_0$ tension, which in turn can be readily verified or falsified by the upcoming measurements., Comment: 31 pages, 6 figures; more discussions and references added, final version published in the journal

We proceed to study the $CP$ asymmetry in the angular distributions of $��\to K_S����_��$ decays within a general effective field theory framework including four-fermion operators up to dimension-six. It is found that, besides the commonly considered scalar-vector interference, the tensor-scalar interference can also produce a non-zero $CP$ asymmetry in the angular distributions. Bounds on the effective couplings of the non-standard scalar and tensor interactions are obtained under the combined constraints from the measured $CP$ asymmetries and the branching ratio of $��^-\to K_S��^-��_��$ decay, with $\mathrm{Im}[\hat��_S]=-0.008\pm0.027$ and $\mathrm{Im}[\hat��_T]=0.03\pm0.12$, at the scale $��_��=2~\mathrm{GeV}$ in the $\mathrm{\overline{MS}}$ scheme. Using the best-fit values, we also find that the distributions of the $CP$ asymmetries can deviate significantly from the SM expectation in almost the whole $K��$ invariant-mass region. Nevertheless, the current bounds are still plagued by large experimental uncertainties, but will be improved with more precise measurements from Belle II as well as the proposed Tera-Z and STCF facilities. Assuming further that the non-standard scalar and tensor interactions originate from a weakly-coupled heavy new physics well above the electroweak scale, the $SU(2)_L$ invariance of the resulting SMEFT Lagrangian would indicate that very strong limits on $\mathrm{Im}[\hat��_S]$ and $\mathrm{Im}[\hat��_T]$ could also be obtained from the neutron electric dipole moment and the $D^0-\bar{D}^0$ mixing. With the bounds from these processes taken into account, it is then found that, unless there exist extraordinary cancellations between the new physics contributions, neither the scalar nor the tensor interaction can produce any significant effects on the $CP$ asymmetries in the processes considered., 36 pages, 2 tables, and 6 figures; bounds on the NP parameters from other processes together with more discussions and references added, final version to be published in JHEP

We investigate the potential for discovering new physics through the low-energy scattering processes $e^-p\to e^-(��^-)��_c$, which could be accessible in the forthcoming $ep$ scattering experiments once adapted to our proposed setups. In the framework of a general low-energy effective Lagrangian, we demonstrate that, compared with the conventional flavor-changing neutral-current weak decays of charmed hadrons and the dilepton productions at high-energy colliders, the low-energy scattering processes can provide more competitive potentials for hunting the underlying new physics. In some specific leptoquark models, we also show that promising event rates can be expected for both the scattering processes, and point out a possible way to distinguish the experimental signals due to the scalar leptoquarks from those of the vector ones., 18 pages, 4 figures, and 6 tables; details of the amplitudes squared and further discussions added, final version to be published in PRD

In $B_c^- \to J/��(\to ��^+ ��^-)��^-\bar��_��$ decay, the three-momentum $\boldsymbol{p}_{��^-}$ cannot be determined accurately due to the decay products of $��^-$ inevitably include an undetected $��_��$. As a consequence, the angular distribution of this decay cannot be measured. In this work, we construct a {\it measurable} angular distribution by considering the subsequent decay $��^- \to ��^- ��_��$. The full cascade decay is $B_c^- \to J/��(\to ��^+ ��^-)��^- (\to ��^- ��_��)\bar��_��$, in which the three-momenta $\boldsymbol{p}_{��^+}$, $\boldsymbol{p}_{��^-}$, and $\boldsymbol{p}_{��^-}$ can be measured. The five-fold differential angular distribution containing all Lorentz structures of the new physics (NP) effective operators can be written in terms of twelve angular observables $\mathcal{I}_i (q^2, E_��)$. Integrating over the energy of pion $E_��$, we construct twelve normalized angular observables $\widehat{\mathcal{I}}_i(q^2)$ and two lepton-flavor-universality ratios $R(P_{L,T}^{J/��})(q^2)$. Based on the $B_c \to J/��$ form factors calculated by the latest lattice QCD and sum rule, we predict the $q^2$ distribution of all $\widehat{\mathcal{I}}_i$ and $R(P_{L,T}^{J/��})$ both within the Standard Model and in eight NP benchmark points. We find that the benchmark BP2 (corresponding to the hypothesis of tensor operator) has the greatest effect on all $\widehat{\mathcal{I}}_{i}$ and $R(P_{L,T}^{J/��})$, except $\widehat{\mathcal{I}}_{5}$. The ratios $R(P_{L,T}^{J/��})$ are more sensitive to the NP with pseudo-scalar operators than the $\widehat{\mathcal{I}}_{i}$. Finally, we discuss the symmetries in the angular observables and present a model-independent method to determine the existence of tensor operators., 29 pages, 3 figures, matches to the version published in JHEP

In this work, we study the $CP$ asymmetry in the angular distribution of $��\to K_S����_��$ decays, taking into account the known $CP$ violation in $K^0-\bar{K}^0$ mixing. It is pointed out for the first time that, once the well-measured $CP$ violation in the neutral kaon system is invoked, a non-zero $CP$ asymmetry would appear in the angular observable of the decays considered, even within the Standard Model. By employing the reciprocal basis, which is most convenient when a $K_{S(L)}$ is involved in the final state, the $CP$-violating angular observable is derived to be two times the product of the time-dependent $CP$ asymmetry in $K\to ��^+��^-$ and the mean value of the angular distribution in $��^\pm\to K^0(\bar{K}^0)��^\pm\bar��_��(��_��)$ decays. Compared with the Belle results measured in four different bins of the $K��$ invariant mass, our predictions lie within the margins of these measurements, except for a $1.7~��$ deviation for the lowest mass bin. While being below the current Belle detection sensitivity that is of $\mathcal{O}(10^{-3})$, our predictions are expected to be detectable at the Belle II experiment, where $\sqrt{70}$ times more sensitive results will be obtained with a $50~\text{ab}^{-1}$ data sample., 23 pages, 3 figures, and 2 tables; minor corrections, final version published in the journal

In $��_b^0 \to ��_c^+ (\to ��^0 ��^+) ��^- \bar��_��$ decay, the solid angle of the final-state particle $��^-$ cannot be determined precisely since the decay products of the $��^-$ include an undetected $��_��$. Therefore, the angular distribution of this decay cannot be measured. In this work, we construct a {\it measurable} angular distribution by considering the subsequent decay $��^- \to ��^- ��_��$. The full cascade decay is $��_b^0 \to ��_c^+ (\to ��^0 ��^+)��^- (\to ��^- ��_��)\bar��_��$. The three-momenta of the final-state particles $��^0$, $��^+$, and $��^-$ can be measured. Considering all Lorentz structures of the new physics (NP) effective operators and an unpolarized initial $��_b$ state, the five-fold differential angular distribution can be expressed in terms of ten angular observables ${\cal K}_i (q^2, E_��)$. By integrating over some of the five kinematic parameters, we define a number of observables, such as the $��_c$ spin polarization $P_{��_c}(q^2)$ and the forward-backward asymmetry of $��^-$ meson $A_{FB}(q^2)$, both of which can be represented by the angular observables $\widehat{\cal K}_i (q^2)$. We provide numerical results for the entire set of the angular observables $\widehat{\cal K}_i (q^2)$ and $\widehat{\cal K}_i$ both within the Standard Model and in some NP scenarios, which are a variety of best-fit solutions in seven different NP hypotheses. We find that the NP which can resolve the anomalies in $\bar{B} \to D^{(*)} ��^- \bar��_��$ decays has obvious effects on the angular observables $\widehat{\cal K}_i (q^2)$, except $\widehat{\cal K}_{1ss} (q^2)$ and $\widehat{\cal K}_{1cc} (q^2)$., 36 pages, 2 figures, 5 tables, matches to the version published in JHEP

With the hypothesis of minimal flavor violation, we find that there exists a power-aligned relation between the Yukawa couplings of the two scalar doublets in the two-Higgs-doublet model with Hermitian Yukawa matrices. Within such a power-aligned framework, it is found that a simultaneous explanation of the anomalies observed in the electron and muon anomalous magnetic moments can be reached with TeV-scale quasi-degenerate Higgs masses, and the resulting parameter space is also phenomenologically safer under the B-physics, $Z$ and $��$ decay data, as well as the current LHC bounds. Furthermore, the flavor-universal power that enhances the charged-lepton Yukawa couplings prompts an interesting correlation between the two anomalies, which makes the model distinguishable from the (generalized) linearly aligned and the lepton-specific two-Higgs-doublet models that address the same anomalies but in a non-correlative manner, and hence testable by future precise measurements., v1: 23 pages, 2 figures; v2: more discussions and references added, final version published in the journal; v3: figure 2 updated by including the latest Fermilab Muon g-2 result, and the lower bound on the charged-Higgs mass changed from 1.4TeV to 1.7TeV, conclusion unchanged

Motivated by the $2.8��$ discrepancy observed between the BaBar measurement and the Standard Model prediction of the CP asymmetry in $��\to K_S����_��$ decays, as well as the prospects of future measurements at Belle II, we revisit this observable in this paper. Firstly, we reproduce the known CP asymmetry due to $K^0 -\bar{K}^0$ mixing by means of the reciprocal basis, which is convenient when a $K_{S(L)}$ is involved in the final state. As the $K��$ tensor form factor plays a crucial role in generating a non-zero direct CP asymmetry that can arise only from the interference of vector and tensor operators, we then present a dispersive representation of this form factor, with its phase obtained in the context of chiral theory with resonances, which fulfills the requirements of unitarity and analyticity. Finally, the $��\to K_S����_��$ decays are analyzed both within a model-independent low-energy effective theory framework and in a scalar leptoquark scenario. It is observed that the CP anomaly can be accommodated in the model-independent framework, even at the $1��$ level, together with the constraint from the branching ratio of $��^-\to K_S��^-��_��$ decay; it can be, however, marginally reconciled only at the $2��$ level, due to the specific relation between the scalar and tensor operators in the scalar leptoquark scenario. Once the combined constraints from the branching ratio and the decay spectrum of this decay are taken into account, these possibilities are however both excluded, even without exploiting further the stronger bounds from the (semi-)leptonic kaon decays under the assumption of lepton-flavour universality, as well as from the neutron electric dipole moment and $D-\bar{D}$ mixing under the assumption of $SU(2)$ invariance of the weak interactions., 41 pages, 8 figures, and 1 table; more references and discussions added, final version published in the journal

In the past few years, several hints of lepton flavour universality (LFU) violation have emerged in the $b \to c ��\bar��$ and $b \to s \ell^+ \ell^-$ data. Quite recently, the Belle Collaboration has reported the first measurement of the $D^*$ longitudinal polarization fraction in the $B \to D^* ��\bar��$ decay. Motivated by this intriguing result, together with the recent measurements of $R_{J/��}$ and $��$ polarization, we study $b \to c ��\bar��$ decays in the Supersymmetry (SUSY) with $R$-parity violation (RPV). We consider $B \to D^{(*)} ��\bar��$, $B_c \to ��_c ��\bar��$, $B_c \to J/����\bar��$ and $��_b \to ��_c ��\bar��$ modes and focus on the branching ratios, the LFU ratios, the forward-backward asymmetries, polarizations of daughter hadrons and $��$ lepton. It is found that the RPV SUSY can explain the $R_{D^{(*)}}$ anomalies at $2��$ level, after taking into account various flavour constraints. In the allowed parameter space, the differential branching fractions and LFU ratios are largely enhanced by the SUSY effects, especially in the large dilepton invariant mass region. In addition, a lower bound $\mathcal B(B^+ \to K^+ ��\bar��) > 7.37 \times 10^{-6}$ is obtained. These observables could provide testable signatures at the High-Luminosity LHC and SuperKEKB, and correlate with direct searches for SUSY., 32 pages, 5 figures, to be published in Chinese Physics C. arXiv admin note: text overlap with arXiv:1905.01795

In the framework of perturbative QCD, the radiative decays $J/��\rightarrow����^{(\prime)}$ are revisited in detail, where the involved one-loop integrals are evaluated analytically with the light quark masses kept. We have found that the sum of loop integrals is insensitive to the light quark masses and the branching ratios $\mathcal{B}(J/��\rightarrow����^{(\prime)})$ barely depend on the shapes of $��^{(\prime)}$ distribution amplitudes. With the parameters of $��-��^{\prime}$ mixing extracted from low energy processes and $J/��\rightarrow����^{(\prime)}$ by means of nonperturbative matrix elements $\langle0|G_{����}^a\tilde{G}^{a,����}|��^{(\prime)}\rangle$ based on $U_{A}(1)$ anomaly dominance argument, we could not give the ratio $R_{J/��}$ in agreement with experimental result. However, using the parameters, especially the mixing angle $��=33.5^{\circ}\pm0.9^{\circ}$, extracted from $��^{\ast}��-��^{\prime}$ transition form factor measured at $q^{2}=112~\mathrm{GeV}^{2}$ by BaBar collaboration, we obtain $R_{J/��}=4.70$ in good agreement with $R_{J/��}^{exp}=4.65\pm0.21$. As a crossing check, with $��^{exp}(��^{(\prime)}\rightarrow����)$ and our results for $J/��\rightarrow����^{(\prime)}$, we get $��=33.9^{\circ}\pm0.6^{\circ}$. The difference between the determinations of $��$ is briefly discussed., 27 pages, 8 figures

During the past few years, hints of Lepton Flavour Universality (LFU) violation have been observed in $b \to c ��\bar��$ and $b \to s \ell^+ \ell^-$ transitions. Recently, the $D^*$ and $��$ polarization fractions $P_L^{D^*}$ and $P_L^��$ in $B \to D^* ��\bar��$ decay have also been measured by the Belle collaboration. Motivated by these intriguing results, we revisit the $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies in a scalar leptoquark (LQ) model, in which two scalar LQs, one being $SU(2)_L$ singlet and the other $SU(2)_L$ triplet, are introduced simultaneously. We consider five $b \to c ��\bar��$ mediated decays, $B \to D^{(*)}��\bar��$, $B_c \to ��_c ��\bar��$, $B_c \to J/����\bar��$, and $��_b \to ��_c ��\bar��$, and focus on the LQ effects on the $q^2$ distributions of the branching fractions, the LFU ratios, and the various angular observables in these decays. Under the combined constraints by the available data on $R_{D^{(*)}}$, $R_{J/��}$, $P_L^��(D^*)$, and $P_L^{D^*}$, we perform scans for the LQ couplings and make predictions for a number of observables. It is found numerically that both the differential branching fractions and the LFU ratios are largely enhanced by the LQ effects, with the latter being expected to provide testable signatures at the SuperKEKB and High-Luminosity LHC experiments., 35 pages, 5figures

In this paper, motivated by the observation that the Standard Model predictions are now above the experimental data for the mass difference $ΔM_{s(d)}$, we perform a detailed study of $B_{s(d)}-\bar{B}_{s(d)}$ mixing and $B_s\toμ^+μ^-$ decay in the $\mathbb{Z}_3$-invariant NMSSM with non-minimal flavour violation, using the recently developed procedure based on the Flavour Expansion Theorem, with which one can perform a purely algebraic mass-insertion expansion of an amplitude written in the mass eigenstate basis without performing any diagrammatic calculations in the interaction/flavour basis. Specifically, we consider the finite orders of mass insertions for neutralinos but the general orders for squarks and charginos, under two sets of assumptions for the squark flavour structures (\textit{i.e.}, while the flavour-conserving off-diagonal element $δ_{33}^\text{LR}$ is kept in both of these two sectors, only the flavour-violating off-diagonal elements $δ_{23}^\text{LL}$ and $δ_{i3}^\text{RR}$ ($i=1,2$) are kept in the \text{LL} and \text{RR} sectors, respectively). Our analytic results are then expressed directly in terms of the initial Lagrangian parameters in the interaction/flavour basis, making it easy to impose the experimental bounds on them. It is found numerically that the NMSSM effects with the above two assumptions for the squark flavour structures can accommodate the observed deviation for $ΔM_{s(d)}$, while complying with the experimental constraints from the branching ratios of $B_s\to μ^+ μ^-$ and $B\to X_sγ$ decays., 48 pages, 7 figures, and 2 tables; More discussions and references added, final version to be published in JHEP

In this paper, we test the self-consistencies of the standard and the covariant light-front quark model and study the zero-mode issue via the decay constants of pseudoscalar ($P$), vector ($V$) and axial-vector ($A$) mesons, as well as the $P\to P$ weak transition form factors. With the traditional type-I correspondence between the manifestly covariant and the light-front approach, the resulting $f_{V}$ as well as $f_{^1\!A}$ and $f_{^3\!A}$ obtained with the $\lbd=0$ and $\lbd=\pm$ polarization states are different from each other, which presents a challenge to the self-consistency of the covariant light-front quark model. However, such a self-consistency problem can be "resolved" within the type-II scheme, which requires an additional replacement $M\to M_0$ relative to the type-I case. Moreover, the replacement $M\to M_0$ is also essential for the self-consistency of the standard light-front quark model. In the type-II scheme, the valence contributions to the physical quantities~(${\cal Q}$) considered in this paper are alway the same as that obtained in the standard light-front quark model, $[{\cal Q}]_{\rm val.}=[{\cal Q}]_{\rm SLF}$, and the zero-mode contributions to $f_{V,^1\!A,^3\!A}$ and $f_-(q^2)$ exist only formally but vanish numerically, which implies further that $[{\cal Q}]_{\rm val.}\dot{=} [{\cal Q}]_{\rm full}$. In addition, the manifest covariance of the covariant light-front quark model is violated in the traditional type-I scheme, but can be recovered by taking the type-II scheme., 37 pages, 5 figures, to be published in Phys. Rev. D

Leptoquarks have been suggested to solve a variety of discrepancies between the expected and observed phenomenon. In this paper, we investigate the effect of scalar leptoquarks on the lepton flavor violating B meson rare decays which involve the quark level transition $\bar{b} \to \bar{s} \ell^-_i \ell^+_j(i \neq j)$. The leptoquark parameter space is constrained by using the recently measured upper limits on the $\mathcal{B}(B_s^0 \to \ell^-_i \ell^+_j)$ and $\mathcal{B}(B \to K^{(*)}\ell^-_i \ell^+_j)$. Using such constrained leptoquark parameter space, some relevant physical quantities are also predicted and we find that the constrained New Physics parameters in the leptoquark model have very obvious effects on the relevant physical quantities in this paper. With future measurements of observable in $B \to K^{(*)}\ell^-_i \ell^+_j$ decays at the LHCb, more and more differentiated from the other NP explanations could be tested., 16 pages;5 figures Appendix; publication in International Journal of Theoretical Physics

The $R(D^{(\ast)})$ anomalies observed in $B\to D^{(\ast)}����$ decays have attracted much attention in recent years. In this paper, we study the $B\to D^{(\ast)}����$, $��_b\to��_c����$, $B_c\to (J/��,\,��_c)����$, $B\to X_c����$, and $B_c\to����$ decays, all being mediated by the same quark-level $b\to c����$ transition, in the Standard Model Effective Field Theory. The most relevant dimension-six operators for these processes are $Q_{lq}^{(3)}$, $Q_{ledq}$, $Q^{(1)}_{lequ}$, and $Q^{(3)}_{lequ}$ in the Warsaw basis. Evolution of the corresponding Wilson coefficients from the new physics scale $��=1$~TeV down to the characteristic scale $��_b\simeq m_b$ is performed at three-loop in QCD and one-loop in EW/QED. It is found that, after taking into account the constraint ${\cal B}(B_c\to����)\lesssim 10\%$, a single $\left[C_{lq}^{(3)}\right]_{3323}(��)$ or $\left[C^{(3)}_{lequ}\right]_{3332}(��)$ can still be used to resolve the $R(D^{(\ast)})$ anomalies at $1��$, while a single $\left[C^{(1)}_{lequ}\right]_{3332}(��)$ is already ruled out by the measured $R(D^{(\ast)})$ at more than $3��$. By minimizing the $��^2(C_i)$ function constructed based on the current data on $R(D)$, $R(D^\ast)$, $P_��(D^\ast)$, $R(J/��)$, and $R(X_c)$, we obtain eleven most trustworthy scenarios, each of which can provide a good explanation of the $R(D^{(\ast)})$ anomalies at $1��$. To further discriminate these different scenarios, we predict thirty-one observables associated with the processes considered under each NP scenario. It is found that most of the scenarios can be differentiated from each other by using these observables and their correlations., 43 pages, 3 figures and 5 tables; references updated and more discussions added, final version to be published in the journal

We show in this paper that, in a $U(1)$-symmetric two-Higgs-doublet model (2HDM), the two additional neutral Higgs bosons would become nearly degenerate in the large $\tan\beta$ regime, under the combined constraints from both theoretical arguments and experimental measurements. As a consequence, the excess observed in the anomalous magnetic moment of the muon could not be addressed in the considered framework, following the usual argument where these two neutral scalars are required to manifest a large mass hierarchy. On the other hand, we find that, with an $\mathcal{O}(1)$ top-Yukawa coupling and a relatively light charged Higgs boson, large contributions from the two-loop Barr-Zee type diagrams can account for the muon $g-2$ anomaly at the 1$\sigma$ level, in spite of a large cancellation between the scalar and pseudoscalar contributions. Furthermore, the same scenario can survive the tight constraints from the $B$-physics observables., Comment: v1:10 pages, 4 figures; v2: more discussions and references added, some references updated, final version published in PRD; v3:plots and numerical analyses updated by including the latest Fermilab Muon g-2 result as well the updated oblique parameters and the B-meson mixing observable, conclusion unchanged

Recently, several $B$-physics experiments report interesting anomalies in the semi-leptonic decays of $B$-mesons, such as the excess in the $R_{D^{(\ast)}}$ measurements. These anomalies seem to suggest intriguing hints of lepton flavor non-universality, and the R-parity violating (RPV) interactions are candidates for explaining this non-universality. In this paper, we discuss the RPV interactions for resolving the $R_{D^{(\ast)}}$ anomaly with the Grand Unified Theory (GUT) assumption. To solve the $R_{D^{(\ast)}}$ anomaly, it is known that large RPV couplings and around $1~{\rm TeV}$ sfermion masses are required. At the same time, large RPV couplings are conducive to realize the bottom-tau Yukawa unification which appears in the GUT models. On the other hand, there are problems for realizing favorable sfermion masses in the constrained minimal supersymetric standard model. To resolve these problems, we show that two non-universalities, the non-universal sfermion masses and the non-universal gaugino masses, are favorable., Comment: 21 pages, 2 tables, 6 figures; more discussions and references added, final version to be published in PRD

Given that the two-Higgs-doublet model of type III (2HDM-III) has the potential to address the $R_{D^{(\ast)}}$ anomalies while the resolution to the $R_{K^{(\ast)}}$ deficits requires new degrees of freedom within this framework, we consider in this paper a unified scenario where the low-scale type-I seesaw mechanism is embedded into the 2HDM-III, so as to accommodate the $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$ anomalies as well as the neutrino mass. We first revisit the $R_{D^{(\ast)}}$ anomalies and find that the current world-averaged results can be addressed at $2\sigma$ level without violating the bound from the branching ratio $\mathcal{B}(B_c^-\rightarrow \tau^- \bar{\nu})\leqslant 30\%$. The scenario predicts two sub-eV neutrino masses based on a decoupled heavy Majorana neutrino and two nearly degenerate Majorana neutrinos with mass around the electroweak scale. For the $R_{K^{(\ast)}}$ anomalies, the same scenario can generate the required Wilson coefficients in the direction $ C_{9 \mu}^{\rm NP}=-C_{10 \mu}^{\rm NP}, Comment: 32 pages, 4 figures; More discussions and references added, final version to be published in JHEP

The rare baryonic decay $��_b\to ��(\to p��^-)��^+��^-$ provides valuable complementary information compared to the corresponding mesonic $b\to s��^+��^-$ transition. In this paper, using the latest high-precision lattice QCD calculation of the $��_b\to��$ transition form factors, we study this interesting decay within the aligned two-Higgs-doublet model, paying particularly attention to effects of the chirality-flipped operators generated by the charged scalars. In order to extract the full set of angular coefficients in this decay, we consider the following ten angular observables that can be derived from the analysis of the subsequent parity-violating $��\to p��^-$ decay: the differential branching fraction ${\rm d}{\cal B}/{\rm d}q^2$, the longitudinal polarization fraction $F_L$, the lepton-, hadron- and combined lepton-hadron-side forward-backward asymmetries $A_{\rm FB}^\ell$, $A_{\rm FB}^��$ and $A_{\rm FB}^{\ell��}$, as well as the other five asymmetry observables $Y_i$~($i={\rm 2,\,3s,\,3sc,\,4s,\,4sc}$). Detailed numerical comparisons are made between the SM and NP values for these angular observables. It is found that, under the constraints from the inclusive $B\to X_s��$ branching fraction and the latest global fit results of $b\to s\ell\ell$ data, the contributions of right-handed semileptonic operators $O^{\prime}_{9,10}$, besides reconciling the $P_5^{\prime}$ anomaly observed in $B^0\to K^{\ast 0}��^+��^-$ decay, could also enhance the values of ${\rm d}{\cal B}/{\rm d}q^2$ and $A_{\rm FB}^\ell$ in the bin $[15,20]~{\rm GeV}^2$, leading to results consistent with the current LHCb measurements., 26 pages, 2 figures, and 4 tables; More discussions added, final version published in the journal

It has been shown that the anomalies observed in $\bar B\to D^{(\ast)}��\bar��_��$ and $\bar B\to \bar K\ell^+\ell^-$ decays can be resolved by adding a single scalar or vector leptoquark to the Standard Model, while constraints from other precision measurements in the flavour sector can be satisfied without fine-tuning. To further explore these two interesting scenarios, in this paper, we study their effects in the semi-leptonic $��_b\to��_c��\bar��_��$ decay. Using the best-fit solutions for the operator coefficients allowed by the current data of mesonic decays, we find that (i) the two scenarios give similar amounts of enhancements to the branching fraction $\mathcal B(��_b\to��_c��\bar��_��)$ and the ratio $R_{��_c}=\mathcal B(��_b\to��_c ��\bar��_��)/\mathcal B(��_b\to��_c\ell\bar��_\ell)$, (ii) the two best-fit solutions in each of these two scenarios are also indistinguishable from each other, (iii) both scenarios give nearly the same predictions as those of the Standard Model for the longitudinal polarizations of $��_c$ and $��$ as well as the lepton-side forward-backward asymmetry. With future measurements of these observables in $��_b\to��_c��\bar��_��$ decay at the LHCb, the two leptoquark scenarios could be further tested, and even differentiated from the other NP explanations for the $R_{D^{(\ast)}}$ anomalies. We also discuss the feasibility for the measurements of these observables at the LHC and the future $e^+e^-$ colliders., 29 pages, 4 tables and 2 figures; More references and the feasibility for the measurements of the observables in these decays at the LHC and the future $e^+e^-$ colliders added, final version published in the journal

We analyze the baryonic semilepton decay $��_{b} \rightarrow$ $����^{+} ��^{-}$ in the scalar leptoquark models with $X(3,2,7/6)$ and $X(3,2,1/6)$ states, respectively. We also discuss the effects of this two NP models on some physical observables. For some measured observables, like the differential decay width, the longitudinal polarization of the dilepton system, the lepton-side forward-backward asymmetry and the baryon-side forward-backward asymmetry, we find, the prediction values of SM are consistent with the current data in the most $q^{2}$ ranges, where the prediction values of this two NP models can also keep consistent with the current data with $1��$. However, in some $q^{2}$ ranges, the prediction values of SM are difficult to meet the current data, but the contributions of this two NP models can meet them or keep closer to them. For the double lepton polarization asymmetries, $P_{LT}$, $P_{TL}$, $P_{NN}$ and $P_{TT}$ are sensitive to the scalar leptoquark model $X(3,2,7/6)$ but not to $X(3,2,1/6)$. However, $P_{LN}$, $P_{NL}$, $P_{TN}$ and $P_{NT}$ are not sensitive to this two NP models., 9 papers, 7 figures. Received 20 April 2016. Accepted 14 July 2016 in Advances in High Energy Physics

In the aligned two-Higgs-doublet model, we perform a complete one-loop computation of the short-distance Wilson coefficients $C_{7,9,10}^{(\prime)}$, which are the most relevant ones for $b\to s\ell^+\ell^-$ transitions. It is found that, when the model parameter $\left|��_u\right|$ is much smaller than $\left|��_d\right|$, the charged-scalar contributes mainly to chirality-flipped $C_{9,10}^\prime$, with the corresponding effects being proportional to $\left|��_d\right|^2$. Numerically, the charged-scalar effects fit into two categories: (A) $C_{7,9,10}^\mathrm{H^\pm}$ are sizable, but $C_{9,10}^{\prime\mathrm{H^\pm}}\simeq0$, corresponding to the (large $\left|��_u\right|$, small $\left|��_d\right|$) region; (B) $C_7^\mathrm{H^\pm}$ and $C_{9,10}^{\prime\mathrm{H^\pm}}$ are sizable, but $C_{9,10}^\mathrm{H^\pm}\simeq0$, corresponding to the (small $\left|��_u\right|$, large $\left|��_d\right|$) region. Taking into account phenomenological constraints from the inclusive radiative decay $B\to X_s��$, as well as the latest model-independent global analysis of $b\to s\ell^+\ell^-$ data, we obtain the much restricted parameter space of the model. We then study the impact of the allowed model parameters on the angular observables $P_2$ and $P_5'$ of $B^0\to K^{\ast 0}��^+��^-$ decay, and find that $P_5'$ could be increased significantly to be consistent with the experimental data in case B., 34 pages, 8 figures, 2 tables; More references and discussions added, final version published in the journal

We revisit the rare leptonic decay $B_s \to ��^+ ��^-$ in the two-Higgs doublet models with a softly broken $Z_2$ symmetry, namely type-I, type-II, type-X and type-Y 2HDMs. We have derived the relevant full one-loop Wilson coefficients of the four 2HDMs from the recent calculation in the aligned two-Higgs doublet model by Li, Lu and Pich, which could be mapped to all the four 2HDMs for both large and small $\tan��$. It is found that, a new term associated with the soft $Z_2$ symmetry breaking parameter $M$ can be enhanced by $\tan^2��$ in the type-II 2HDM, which has not been considered in the literature. Imposing both theoretical and experimental constraints, we have renewed the bounds on the parameter spaces of the four 2HDMs. Different from our previous paper, however, we find that all the four 2HDMs give sizable and similar contributions to $\overline{\mathcal B}(B_s \to ��^+ ��^-)$ within the stringently restricted parameter spaces, but very tiny as regards the mass-eigenstate rate asymmetry $\mathcal A_{����}$; this makes it unfeasible to discriminate the four types of 2HDM with the correlations between the observables in $B_s \to ��^+ ��^-$ decay., 27 pages, 2 tables, 4 figures; v2: a brief introduction to 2HDM added, matches published version

We study the rare decays $D^+\to ��^{+}\ell^+\ell^-$, $D^+_s\to K^{+}\ell^+\ell^-$ and $D^0\to \ell^+\ell^-(\ell=e,��)$ in the minimal supersymmetic standard model with and without R-parity. Using the strong constraints on relevant supersymmetric parameters from $D^0-\bar{D}^0$ mixing and $K^+\to ��^+��\bar��$ decay, we examine constrained supersymmetry contributions to relevant branching ratios, direct CP violations and ratios of $D^+_{(s)}\to ��(K)^{+}��^+��^-$ and $D^+_{(s)}\to ��(K)^{+}e^+e^-$ decay rates. We find that both R-parity conserving LR as well as RL mass insertions and R-parity violating squark exchange couplings have huge effects on the direct CP violations of $D^+_{(s)}\to ��(K)^{+}\ell^+\ell^-$, moreover, the constrained LR and RL mass insertions still have obvious effects on the ratios of $D^+_{(s)}\to ��(K)^{+}��^+��^-$ and $D^+_{(s)}\to ��(K)^{+}e^+e^-$ decay rates. The direct CP asymmetries and the ratios of $D^+_{(s)}\to ��(K)^{+}��^+��^-$ and $D^+_{(s)}\to ��(K)^{+}e^+e^-$ decay rates are very sensitive to both moduli and phases of relevant supersymmetric parameters. In addition, the differential direct CP asymmetries of $D^+_{(s)}\to ��(K)^{+}\ell^+\ell^-$ are studied in detail., 18 pages, 9 figures

In the "Higgs basis" for a generic 2HDM, only one doublet gets a nonzero vacuum expectation value and, under the criterion of minimal flavour violation, the other one is fixed to be either colour-singlet or colour-octet, referred respectively as the type-III and the type-C model. Both of them can naturally avoid large FCNC transitions and provide very interesting phenomena in some low-energy processes. In this paper, we study their effects on exclusive radiative B-meson decays due to the exchange of colourless or coloured charged Higgs. It is found that, while constraints from the branching ratios are slightly weaker than the ones from the inclusive $B\to X_{s} \gamma$ decay, the isospin asymmetries in exclusive decays provide very complementary bounds on the model parameters. As the two models predict similar corrections to the dipole coefficient $C_7^{\rm eff}$ whereas similar magnitudes but with opposite signs to $C_8^{\rm eff}$, the branching ratios cannot discriminate the two models, and we have to resort to the direct CP and isospin asymmetries of $b\to s$ processes, which are more sensitive to $C_8^{\rm eff}$. Due to the CKM factors $|\lambda_u^{(d)}|\sim|\lambda_t^{(d)}|$, the terms proportional to $\lambda_u^{(d)}$ make the observables of $b\to d$ processes exhibit a different dependence on the possible new physics phase. In addition, correlations between the various observables in the exclusive $B\to V\gamma$ and the inclusive $B\to X_{s,d}\gamma$ decays are investigated, which could provide further insights into the models with more precise experimental measurements and theoretical predictions for these decays., Comment: 38 pages, 9 figures, 3 tables; more references and discussions added, matches version published in PRD

In this paper, we analyze the possible anomalous $tcZ$ coupling effects in the $b \to s $ mediated decays $\bar B \to \bar K^* ��^+ ��^-$ and $B_s \to ��^+ ��^-$. After exploiting the available experimental data, the combined constraints on the anomalous coupling $X_{ct}^L$ are derived. It is found that, the bound on the magnitude $|X_{ct}^L|$ is dominated by the branching ratios of these two decays. Furthermore, one sign-flipped solution is excluded by the longitudinal fraction of $\bar B \to \bar K^* ��^+ ��^-$ at the low dilepton mass region. After considering the combined constraints, for general complex coupling $X_{ct}^L$, the predicted upper bound on $\mathcal B (t \to cZ)$ are compatible with that from the recent CMS direct search. In particular, for the case of real coupling $X_{ct}^L$, the upper bound reads $\mathcal B (t \to cZ), 23 pages, 9 figures, 2 tables. v3: effects due to the width difference \Delta\Gamma_s added, numerical results and figure.3 and 4 slightly changed, main conclusions of the paper remain the same, matches published version in JHEP

Recently, the large CP asymmetries in $B^\pm\to��^\pm��^+��^-$ decays were found by the LHCb Collaboration to localize in the region $m_{��^+��^-}^2, 5 pages, 1 figure, 1 table, to be published on Physical Review D

We calculate the branching ratio of a bottom hadron decaying into a charmed hadron and a charged $��$ meson within the QCD factorization approach. We consider the effect of the finite width correction of the $��$ meson. Our numerical calculation shows an obvious correction because of this effect. We find that the finite width effect of the $��$ meson reduces the branching ratios by about 9% to 11% for bottom meson decay channels: $B^+\to\bar{D^0}��^+$, $B^0\to D^-��^+$, and $B^0_s\to D^-_s��^+$, and increases the branching ratio by about 10% for $��_b^0\to��_c^+��^-$., 12 pages

Large CP violation is an interesting phenomenon both theoretically and experimentally. Last year, LHCb Collaboration found in some three-body decays of bottom mesons that large CP violations appear in regions of the Dalitz plots that are not dominated by contributions from narrow resonances. In this paper, we present a mechanism which can induce such kind of large CP violations. In this mechanism, large localized CP asymmetries in phase space can be induced by the interference of two intermediate resonances with different spins. We also apply this mechanism to the decay channel $B^\pm\to K^\pm \pi^+\pi^-$., Comment: 11 pages, 1 figure

Motivated by the latest improved measurements of B-meson decays, we make a comprehensive analysis of the impact of a family non-universal $Z^{\prime}$ boson on $B_s-\bar{B}_s$ mixing and two-body hadronic B-meson decays, all being characterized by the quark-level $b\to s$ transition. Explicitly 22 decay modes and the related 52 observables are considered, and some interesting correlations between them are also carefully examined. Firstly, the allowed oases of $b-s-Z^{\prime}$ coupling parameters $|B^{L,R}_{sb}|$ and $��^{L,R}_s$ are extracted from $B_s-\bar{B}_s$ mixing. Then, in the "SM limit"~({\it i.e.,} no new types of $Z^{\prime}$-induced four-quark operators arise compared to the SM case), we study the $Z^{\prime}$ effects on $B\to��K$, $��K^{\ast}$ and $��K$ decays. It is found that a new weak phase $��^{L}_s\sim -90^{\circ}$ is crucial for resolving the observed "$��K$ CP puzzle" and the allowed oases of the other $Z^{\prime}$ coupling parameters are also strongly restricted. Moreover, the $Z^{\prime}$ effects on $\bar{B}_s\to K K$, $K K^{\ast}$ and $��^0 ��$ decays, being induced by the same quark-level $b\to s q\bar{q}~(q=u,d)$ transitions, are also investigated. Especially, it is found that the decay $\bar{B}_s \to ��^0 ��$, once measured, would play a key role in revealing the observed "$��K$ CP puzzle" and probing possible new physics hints. Finally, to check the non-universality of $Z^{\prime}$ couplings to light-quark pairs, we have studied the $B\to ��K$ decays in detail and found that the left-handed $s-s-Z^{\prime}$ coupling is different from the $d-d-Z^{\prime}$ one, which is due to the large $A_{CP}^{dir}(B^-\to��K^-)$ reported by the BaBar collaboration., 38 pages, 11 figures; To appear in JPG

Motivated by the recent measurements of non-leptonic $\bar{B}_s^0$ decays by CDF and LHCb collaborations, especially the large ${\cal B}(\bar{B}_s^0\to\pi^+\pi^-)$, we revisit the hard spectator and annihilation corrections in $\bar{B}_s^0$ decays within QCD factorization approach with two schemes for the possible parameters for the known end-point divergence appeared in the estimation of the hard spectator and annihilation diagrams. The first one is to conservatively estimate the possible contributions by parameterization (scheme I); another one uses an infrared finite gluon propagator (scheme II) to regulate the end-point singularity. In scheme I, with the constraints from the measured $\bar{B}_s^0\to PP (VV)$ decays, two (four) restricted solutions of the parameters spaces are found. In scheme II, we find that most of the theoretical predictions agree well with the experimental data with single parameter $m_{g}\sim 0.5{\rm GeV}$. However, within both schemes, ${\cal B}(\bar{B}_s^0\to\phi\phi)$ are always much larger than ${\cal B}(\bar{B}_s^0\to K^{\ast 0}\bar{K}^{\ast 0})$ in contrast to the experimental results ${\cal B}(\bar{B}_s^0\to\phi\phi)\simeq{\cal B}(\bar{B}_s^0\to K^{\ast 0}\bar{K}^{\ast 0})$. It is noted that the pattern ${\cal B}(\bar{B}_s^0\to\phi\phi)>{\cal B}(\bar{B}_s^0\to K^{\ast 0}\bar{K}^{\ast 0})$ also persists in other theoretical framework, thus the present experimental result ${\cal B}(\bar{B}_s^0\to\phi\phi) \simeq {\cal B}(\bar{B}_s^0\to K^{\ast 0}\bar{K}^{\ast 0})$ rises a challenge to theoretical approaches for B non-leptonic decays. Further refined measurements and theoretical studies are called for to resolve such a possible anomaly., Comment: 25pages, 6 figures; minor typos corrected; version to appear in Phys. Rev. D

Motivated by the recently observed anomalous large dimuon charge asymmetry in neutral B decays and the unexpected large CP phase in the mixing-induced CP asymmetry for B_s-->J/\psi\phi decay, we study the effects of the anomalous tensor couplings to pursue possible solution. With the constraints from the obsevables \phi^{J/\psi\phi}_s, a_{sl}^s and \Delta M_s, the parameter spaces are severely restricted. Numerically, we find the anomalies in B_s^0-\bar{B}_s^0 mixing system could be moderated simultaneously by the contributions induced by the color-singlet or color-octet tensor operators with their respective nontrivial new weak phase \phi_{T1}\approx28.0(15.6) degree or \phi_{T8}\approx-62.1(-74.2) degree and relevant strength parameters g_{T1}\approx6.7(8.5)\times10^{-2} or g_{T8}\approx1.9(2.4)\times10^{-2} for the CP-violating phase \phi^{J/\psi\phi}_s=-0.77(+0.29,-0.37)(-2.36(+0.37,-0.29)), respectively., Comment: 14pages, 2 figures, 3tables

Recent results from CDF and D{\O} collaborations favor a large CP asymmetry in B_s^0-\bar{B}_s^0 mixing, while the standard model prediction is very small. Such a large phase may imply sizable new physics effects in B_s^0-\bar{B}_s^0 mixing. We compute the gluino-mediated supersymmetry contributions to B_s^0-\bar{B}_s^0 mixing, B_s->K^{(*)-}K^{(*)+} and B->X_s\gamma decays in the frame of the mass insertion approximation. Combining the constraints of \DeltaM_s, \Delta\Gamma_s, \phi^{J/\psi\phi}_s, B(B_s->K^{-}K^{+}) and B(B->X_s \gamma), we find that the effects of the constrained LL and RR insertions in B_s->K^{(*)-}K^{(*)+} decays are small because of the absence of gluino mass enhancement. For m^2_{\tilde{g}}/m^2_{\tilde{q}}=9, the constrained LR insertion can provide sizable contributions to all observables of B_s->K^{(*)-}K^{(*)+} decays except A^{dir}_{CP}(B_s->K^{-}K^{+}), and many observables are sensitive to the modulus and the phase of the LR insertion parameter. Near future experiments at Fermilab Tevatron and CERN LHC-b can test these predictions and shrink/reveal the mass insertion parameter spaces., Comment: 28 pages and 9 figures, published version, 3 figures added

The top-quark FCNC processes will be searched for at the CERN LHC, which are correlated with the B-meson decays. In this paper, we study the effects of top-quark anomalous interactions $tq��$ in the exclusive radiative $B\to K^*��$ and $B\to����$ decays. With the current experimental data of the branching ratios, the direct CP and the isospin asymmetries, bounds on the coupling $��_{tcR}^��$ from $B\to K^*��$ and $��_{tuR}^��$ from $B\to ����$ decays are derived, respectively. The bound on $|��_{tcR}^��|$ from ${\mathcal B}(B\to K^{*}��)$ is generally compatible with that from ${\mathcal B}(B\to X_{s}��)$. However, the isospin asymmetry $��(K^{*}��)$ further restrict the phase of $��_{tcR}^��$, and the combined bound results in the upper limit, $\mathcal B(t\to c��), 25 pages, 15 figures, pdflatex

The rare decays B_s -> ��^+��^- and B -> K^{(*)}��^+��^- are sensitive to new particles and couplings via their interferences with the standard model contributions. Recently, the upper bound on B(B_s -> ��^+��^-) has been improved significantly by the CMS, LHCb, CDF, and D�� experiments. Combining with the measurements of B(B-> K^{(*)}��^+��^-), we derive constraints on the relevant parameters of minimal supersymmetic standard model with and without R-parity, and examine their contributions to the dimuon forward-backward asymmetry in B-> K^{*}��^+��^- decay. We find that (i) the contribution of R-parity violating coupling products ��^{\prime}_{2i2}��^{\prime*}_{2i3} due to squark exchange is comparable with the theoretical uncertainties in B-> K ��^+��^- decay, but still could be significant in B-> K^{*}��^+��^- decay and could account for the forward-backward asymmetry in all dimuon invariant mass regions; (ii) the constrained mass insertion (��^{u}_{LL})_{23} could have significant contribution to dA_{FB}(B-> K^{*}��^+��^-)/ds, and such effects are favored by thr recent results of the Belle, CDF, and LHCb experiments., 20 pages, 9 figures, published version

Motivated by the observed forward-backward asymmetry in $B\to K^{\ast} l^+ l^-$ decay, we perform a detailed analysis of this decay mode within a family non-universal $Z^{\prime}$ model. With the related coupling $Z^{\prime}-\bar{s}b$ constrained by $\bar{B}_s-B_s$ mixing, $B\to \pi K$, and $B\to X_s \mu^{+}\mu^{-}$ decays, we look for further constraint on the couplings $Z^{\prime}-\mu^{+}\mu^{-}$ from $A_{FB}(B\to K^{\ast} \mu^{+}\mu^{-})_{0 {\rm GeV}^2\leqslant q^2\leqslant 2 {\rm GeV}^2}$ and get numerically $B_{\mu\mu}^{L,R}\sim{\cal O}(10^{-2})$. Moreover, we find that the relations, $B_{\mu\mu}^{L}, Comment: 20 pages, 3 figures. To appear in JHEP

Motivated by the measured large branching ratio of $\bar{B}^{0}\to��^0��^0$ (the so-called "$����$" puzzle), we investigate the effects of a family non-universal $Z^{\prime}$ model on the tree-dominated $B\to����$ decays. We find that the $Z^{\prime}$ coupling parameter $��_{d}^{LR}\sim0.05$ with a nontrivial new weak phase $��_d^L\sim-50^{\circ}$, which is relevant to the $Z^{\prime}$ contributions to the QCD penguin sector $\triangle C_5$, is needed to reconcile the observed discrepancy. Combined with the recent fitting results from $B\to��K$, $��K^{\ast}$ and $��K$ decays, the $Z^{\prime}$ parameter spaces are severely reduced but still not excluded entirely, implying that both the "$����$" and "$��K$" puzzles could be accommodated simultaneously within such a family non-universal $Z^{\prime}$ model., 28 pages, 4 figures. References and discussions added. To appear in IJMPA

Observation of top quark flavor changing neutral process $t\to c +��$ at the LHC would be the signal of physics beyond the Standard Model. If anomalous $t\to c��$ coupling exists, it will affect the precisely measured $\mathcal{B}(\bar{B} \to X_s ��)$. In this paper, we study the effects of a dimension 5 anomalous $ tc ��$ operator in $\bar{B} \to X_s ��$ decay to derive constraints on its possible strength. It is found that, for real anomalous $t\to c��$ coupling $��_{\rm{tcR}}^��$, the constraints correspond to the upper bounds $\mathcal B (t \to c + ��)0$) and $\mathcal B (t \to c + ��), 15 pages, 5 figures. Revised. To appear in PRD

We revisit $\bar{B}_s\to ��K$, $��K^{\ast}$ and $��K$ decays within QCDF formalism and examine the possible effects of a family non-universal $Z^\prime$ boson in these decays. In our evaluations, the strong constraints from $B_d-\bar{B_d}$ mixing on the strength of the left-handed flavor-changing $d-b-Z^{\prime}$ coupling $B_{db}^{L}$ ~($\sim0.2\times10^{-3}$) is also included. Numerically, we find that a new weak phase $��^L_d\sim-50^{\circ}$ involved in $B_{db}^{L}$, the negative combination of the $u-u-Z^{\prime}$ and $d-d-Z^{\prime}$ couplings $P_{ud}^{R}$ and/or $D_{ud}^{L}$ with larger absolute value are crucial to improve the agreement of ${\cal B}(\bar{B}_s\to ��^- K^+)$ between the SM prediction and the experimental measurement. Generally, ${\cal B}(\bar{B}_s\to ��^- K^+)$ could be reduced by about 18% at most by $Z^{\prime}$ contributions. Moreover, combining with the recent updated measurement on $��_s$ by CDF and D0 collaborations, we also find that $Z^{\prime}$ effects in $\bar{B}_s\to ��^- K^+$ decays are very important for examining whether the CKM-like hierarchy persists in a family non-universal $Z^{\prime}$ coupling matrix., 20 pages, 4 figures; final version to appear in Nucl. Phys. B

According to the heavy-quark flavour symmetry, the $B\to ��, K$ transition form factors could be related to the corresponding ones of D-meson decays near the zero recoil point. With the recent precisely measured exclusive semileptonic decays $D \to ��\ell ��$ and $D\to K \ell ��$, we perform a phenomenological study of $B \to ��, K$ transition form factors based on this symmetry. Using BK, BZ and Series Expansion parameterizations of the form factor slope, we extrapolate $B \to ��, K$ transition form factors from $q^{2}_{max}$ to $q^{2}=0$. It is found that, although being consistent with each other within error bars, the central values of our results for $B \to ��, K$ form factors at $q^2=0$, $f_+^{B\to ��, K}(0)$, are much smaller than predictions of the QCD light-cone sum rules, but are in good agreements with the ones extracted from hadronic B-meson decays within the SCET framework. Moreover, smaller form factors are also favored by the QCD factorization approach for hadronic B-meson decays., 19 pages, no figure, 5 tables

Motivated by the large discrepancy of CP-violating phase in $\bar{B}_s-B_s$ mixing between the experimental data and the Standard Model prediction, we pursue possible solutions within a family non-universal $Z^{\prime}$ model. Within such a specific model, we find that both the $\bar{B}_s-B_s$ mixing anomaly and the well-known "$��K$ puzzle" could be moderated simultaneously with a nontrivial new weak phase, $��^L_s\sim-72^{\circ}$ (S1) or $-82^{\circ}$ (S2). With the stringently constrained $Z^{\prime}$ coupling $B_{sb}^{L}$, we then study the $Z^{\prime}$ effects on the rare $B\to X_s ��^+��^-$ and $B_s\to ��^+��^-$ decays, which are also induced by the same $b\to s$ transition. The observables of $B\to X_s ��^+��^-$, at both high and low $q^2$ regions, are found to be able to put strong constraints on the $��-��-Z^{\prime}$ coupling, $B_{����}^{L,R}\sim10^{-2}$. It is also shown that the combined constraints from $\bar{B}_s-B_s$ mixing, $B\to ��K$ and $B\to X_s ��^+��^-$ do not allow a large $Z^{\prime}$ contribution to the pure leptonic $B_s\to��^+��^-$ decay., 29 pages, 10 figs and 6 tables. References and discussions added. To appear in JHEP