Recently, the Belle II Collaboration reported the branching fraction $\mathcal{B}(B^+ \to K^+ ν\barν)=(2.3\pm0.7)\times10^{-5}$ with a significance of $3.5σ$, which is $2.7σ$ above the SM expectation. Motivated by this measurement, we calculate this decay channel at the NLO and twist-3 level using the PQCD approach. By combining the lattice QCD data and our results, we obtain form factors with improved accuracy. Using these form factors, we precisely estimate the branching ratios of $B^+ \to K^+$ semileptonic FCNC decays, including $B^+ \to K^+ν\barν$ and $B^+ \to K^+\ell^+\ell^-$. To explain the anomalies in these two processes, we introduce a leptoquark model as a new physics scenario. Using five possible types of leptoquarks, we successfully explain the latest experimental measurements, and further constraints on the leptoquarks are derived.
FCNC in leptonic and semileptonic decays of D mesons in a general two-Higgs doublet model
FCNC半轻子D衰变中大的长距离标准模型效应可以使这些过程在未来的测量中观测到。在这个部门和/或轻子族违反(LFV)D衰变的观察最终的分歧将需要超越SM框架的解释。在本文中,我们面对轻子和半轻子FCNC和LFV D介子衰变的实验数据与版本的两希格斯偶极子模型,允许这些影响发生在树水平。从D ^0-> l^+ l '^-和D -> pi l^+ l'^-衰变中得到了模型参数的严格界。模型的一致性要求D -> Vl ^+ l '^-衰变的分支分数应低于10^{-9}能级。
We revisit rare radiative leptonic decays $B_{s,d}\to γe^+e^-$ and $B_{s,d}\to γμ^+μ^-$ in the Standard Model and provide the updated estimates for various differential distributions (the branching ratios, the forward-backward asymmetry, and $R_{μ/e}$, the ratio of the differential distribution for muons over electrons in the final state). The new ingredients of this work compared to the existing theoretical analyses are the following: (i) we calculate all $B_d\toγ$ and $B_s\toγ$ form factors induced by the vector, axial-vector, tensor and pseudotensor quark currents within the relativistic di…
In this paper we present a phenomenological analysis of the Partially Aligned Two Higgs Doublet Model (PA-2HDM) by using leptonic decays of mesons and $B^0_{d,s}$-$\bar B^0_{d,s}$ mixing. We focus our attention in a scenario where the leading contribution to FCNC is given by the tree level interaction with the light pseudoscalar $A^0$ ($M_{A^0}\sim 250$ GeV). We show how an underlying flavor symmetry controls FCNC in the quark and lepton couplings with the pseudoscalar, without alignment between Yukawa matrices. Upper bounds on the free parameters are calculated in the context of the leptonic …
This presentation reviews the main results of our recent work [A.K., D.M., N.N., Phys. Rev. D97, 053007 (2018)] on rare radiative leptonic decays $B_{d,s}\toγμ^+μ^-$ and $B_{d,s}\toγe^+e ^-$ induced by flavour-changing neutral currents (FCNC) in the Standard Model.
The theoretical calculation of pseudo-scalar leptonic decay widths into an invisible ALP, $M \to \ell\, ν_\ell\, a$, is reviewed. Assuming generic flavour-conserving ALP couplings to SM fermions and a generic ALP mass, $m_a$, the latest experimental results for pseudo-scalar leptonic decays are used to provide updated bounds on the ALP-fermion Lagrangian sector. Constrains on the ALP-quark couplings obtained from these channels are not yet competitive with the ones derived from FCNC processes, like $M\to P\,a$ decays. These leptonic decays can, however, provide the most stringent model-indepen…
The leptonic radiative decay $B \to γlν$ is of great importance in the determination of $B$ meson wave functions, and evaluating the form factors $ F_{V,A}$ are the essential problem on the study of this channel. We computed next-to-leading power corrections to the form factors within the framework of PQCD approach, including the power suppressed hard kernel, the contribution from a complete set of three-particle $B$ meson wave functions up to twist-4 and two-particle off light-cone wave functions, the $1/m_b$ corrections in heavy quark effective theory, and the contribution from hadronic stru…
We analyse $Z^\prime$ contributions to FCNC processes at the one-loop level. In analogy to the CKM matrix we introduce two $3\times3$ unitary matrices $\hatΔ_d(Z^\prime)$ and $\hatΔ_u(Z^\prime)$ which are also hermitian. They govern the flavour interactions mediated by $Z^\prime$ between down-quarks and up-quarks, respectively, with $\hatΔ_d(Z^\prime)=\hatΔ_u(Z^\prime)\equiv \hatΔ_L(Z^\prime)$ for left-handed currents due to the unbroken $\text{SU(2)}_L$ gauge symmetry. This assures the suppression of these contributions to all $Z^\prime$ mediated FCNC processes at the one-loop level. As, in c…
Motivated by recent anomalies in FCNC $b\to s\ell^+\ell^-$, we study $B_1\to B_2\ell^+\ell^-(\ell=e,μ,τ)$ semi-leptonic weak decays with the SU(3) flavor symmetry, where $B_{1,2}$ are the spin-1/2 baryons of single bottomed anti-triplet $T_{b3}$, single charmed anti-triplet $T_{c3}$ or light baryon octet $T_{8}$. Using the SU(3) irreducible representation approach, we first obtain the amplitude relations among different decays, and then predict the relevant not-yet measured observables of these decays. (a) We calculate the branching ratios of the $T_{b3}\to T_8 μ^+μ^-$ and $T_{b3}\to T_8 τ^+τ^…
We present a new determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{\rm cb}|$ by using the three-loop perturbative QCD corrections for the $B\to D^{\ast}$ semi-leptonic decay. The decay width of $B\to D^{\ast}$ semi-leptonic decay can be factorized as perturbatively calculable short-distance part and the non-perturbative but universal long-distance part. We adopt the principle of maximum conformality (PMC) single-scale setting approach to deal with the perturbative series so as to achieve a precise fixed-order prediction for the short-distance parameter $η_{A}$. By applying the…
A $Z^\prime$ Model for $b\to s \ell\bar \ell$ Flavour Anomalies
我们研究了LHCb数据中$b\to s \ell\bar \ell$引起的$B$衰变中出现的几种异常的$SU(2)_l\times SU(2)_h\times U(1)_Y$电弱规范对称性模型中的变味中性电流(FCNC)的含义。在这个模型中,$SU(2)_l$和$SU(2)_h$分别控制前两代和第三代的左手费米子。物理$Z$和$Z'$在树的层次上产生$b\to s$跃迁,导致对$b \to s$半轻子算子${\cal O}_{9,10}$的额外贡献。我们发现,虽然$B_s$-$\bar B_s$混合严格约束的参数,该模型可以产生的${\cal C}^{\rm NP}_{9,10}$值的范围内确定的Descotes-Genon { \it等。al.}参考文献~ \cite{Descotes-Genon:2015uva}的这种情况下,以提高全球拟合的观测衰减引起的$b\to s μ\bar μ$过渡。在这个模型中的$Z'$玻色子也产生树水平的FCNC的轻子相互作用,可以容纳实验中心值的$R_K = {\cal B}(B\to K μ\bar μ)/{\cal B}(B\to K e\bar e)=0.75$。在这种情况下,该模型预测了$B\to K e \bar τ$、$B\to K τ\bar e$的相当大的分支比,以及$B\to K τ\bar τ$相对于其SM值的增强。
We comprehensively study the charged-Higgs contributions to the leptonic $B^-_q \to \ell \bar ν$ ($q=u,c$) and semileptonic $\bar B \to X_q \ell \barν$ ($X_u=π, ρ; X_c=D,D^*$) decays in the type-III two-Higgs-doublet model (2HDM). We employ the Cheng-Sher ansatz to suppress the tree-level flavor-changing neutral currents (FCNCs) in the quark sector. When the strict constraints from the $ΔB=2$ and $b\to s γ$ processes are considered, parameters $χ^u_{tq}$ from the quark couplings and $χ^\ell_\ell$ from the lepton couplings dictate the leptonic and semileptonic $B$ decays. It is found that when …
We study the anomalous FCNC $tqγ$ and $tqg$ couplings via $pp\to Wbγ+X$ signal process including realistic detector effects for both leptonic and hadronic decay channels of the W boson at 100 TeV FCC-hh. The relevant background are considered in the cut based analysis to obtain not only limits on the anomalous $λ$ and $ζ$ couplings but also branching ratios of $t\to qγ$ and $t\to qg$ decay channels. We find that the sensitivity to the branching ratio of $t \to q γ$ channel is three order better than the available LHC experimental limits, and it is comparable for the branching ratio of the $t\t…
Determination of $|V_{\rm cb}|$ using Bayesian analysis of the $B \rightarrow D^{*}\ell {\bar ν}_\ell$ semileptonic decay width with four-loop QCD corrections