$η^{(\prime)}$-meson twist-2 distribution amplitude within QCD sum rule approach and its application to the semi-leptonic decay $ D_s^+ \toη^{(\prime)}\ell^+ ν_\ell$
Dan-Dan Hu, Hai-Bing Fu, Tao Zhong, Long Zeng, Wei Cheng, Xing-Gang Wu
备注：
52 pages, 11 figures, version to be published in EPJC
In this paper, we make a detailed discussion on the $η$ and $η'$-meson leading-twist light-cone distribution amplitude $ϕ_{2;η^{(\prime)}}(u,μ)$ by using QCD sum rules approach under the background field theory. Taking both the non-perturbative condensates up to dimension-six and NLO QCD corrections to the perturbative part, its first three moments $\langleξ^n_{2;η^{(\prime)}}\rangle|_{μ_0} $ with $n = (2,4,6)$ at initial scale $μ_0 = 1$ GeV can be determined. e.g. $\langleξ_{2;η}^2\rangle|_{μ_0} =0.231_{-0.013}^{+0.010}$, $\langleξ_{2;η}^4 \rangle|_{μ_0} =0.109_{-0.007}^{+0.007}$, and $\langleξ_{2;η}^6 \rangle|_{μ_0} =0.066_{-0.006}^{+0.006}$ for $η$-meson, $\langleξ_{2;η'}^2\rangle|_{μ_0} =0.211_{-0.017}^{+0.015}$, $\langleξ_{2;η'}^4 \rangle|_{μ_0} =0.093_{-0.009}^{+0.009}$, and $\langleξ_{2;η'}^6 \rangle|_{μ_0} =0.054_{-0.008}^{+0.008}$ for $η'$-meson. Next, we calculate $D_s\toη^{(\prime)}$ TFFs $f^{η^{(\prime)}}_+(q^2)$ within QCD light-cone sum rules approach up to NLO level. The values at large recoil region are $f^η_+(0) = 0.476_{-0.036}^{+0.040}$ and $f^{η'}_+(0) = 0.544_{-0.042}^{+0.046}$. After extrapolating TFFs to the allowable physical regions within the series expansion, we obtain the branching fractions of the semi-leptonic decay, i.e. $D_s^+\toη^{(\prime)}\ell^+ ν_\ell$, i.e. ${\cal B}(D_s^+\toη^{(\prime)} e^+ν_e)=2.346_{-0.331}^{+0.418}(0.792_{-0.118}^{+0.141})\times10^{-2}$ and ${\cal B}(D_s^+\toη^{(\prime)} μ^+ν_μ)=2.320_{-0.327}^{+0.413}(0.773_{-0.115}^{+0.138})\times10^{-2}$ for $\ell = (e, μ)$ channels respectively. And in addition to that, the mixing angle for $η-η'$ with $φ$ and ratio for the different decay channels ${\cal R}_{η'/η}^\ell$ are given, which show good agreement with the recent BESIII measurements.
The most recent measurements of the observables $R_{D^{(*)}}$ are in tension with the Standard Model offering hints of New Physics in $b\rightarrow c \ell \barν_{\ell}$ transitions. Motivated by these results, in this work we present an analysis on their $b\rightarrow u \ell \barν_{\ell}$ counterparts (for $\ell=e, ~μ, ~τ$). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic $B$ decays ($B^-\rightarrow \ell^- \barν_{\ell}$, $\bar{B}\rightarrow π\ell …
We reconsider the QCD predictions for the radiative decay $B\to γ\ell ν_\ell$ with an energetic photon in the final state by taking into account the $1/E_γ, 1/m_b$ power-suppressed hard-collinear and soft corrections from higher-twist $B$-meson light-cone distribution amplitudes (LCDAs). The soft contribution is estimated through a dispersion relation and light-cone QCD sum rules. The analysis of theoretical uncertainties and the dependence of the decay form factors on the leading-twist LCDA $ϕ_+(ω)$ shows that the latter dominates. The radiative leptonic decay is therefore well suited to cons…
We address the impact of a modified $W \ell ν$ coupling on a wide range of observables, such as $τ$ leptonic and mesonic decays, leptonic decays of pseudoscalar mesons, as well as semileptonic meson decays. In particular, we concentrate on deviations from lepton flavour universality, focusing on the ratios $R_{P} = Γ(P \to \ell ν) / Γ(P \to \ell' ν)$, with $P=K, π, D, D_s$, $R(D)={Γ(B^+ \to D τ^+ ν)}/{Γ(B^+ \to D\ell^+ ν)}$, $R τ={Γ(τ\to μνν)}/{Γ(τ\to eνν)}$, $R^{\ell τ}_P=Γ(τ\to Pν)/Γ(P\to \ell ν)$, and $\text{BR}(B \to τν)$. We further consider leptonic gauge boson decays, such as $W\to \ell…
We analyze the radiative leptonic $B_c$ decay mode: $B_c \to \ell νγ$ ($\ell=e, μ$) using a QCD-inspired constituent quark model. The prediction: ${\cal B}(B_c \to \ell νγ)\simeq 3 \times 10^{-5}$ makes this channel experimentally promising in view of the large number of $B_c$ mesons which are expected to be produced at the future hadron facilities.
We study the effects of the identical leptons in the final state of the $B^+\to \ell^+ \ell^- \ell^+\barν_{\ell}$ decay. The amplitude of the process is described by the same form factors as the amplitude of the ${B\to \ell \ell \ell'\barν'_{\ell}}$ decay for non-identical leptons in the final state. However, the differential distributions are strongly different, as the ${B^+\to \ell^+ \ell^- \ell^+\barν_{\ell}}$ amplitude contains both the direct ($M_a$) and the exchange ($M_b$) diagrams. We calculate a number of the differential distirbutions. In particular, we propose an interesting observa…
With the renewed distribution amplitudes of $Λ$, we present a reanalysis on the semi-leptonic decay $Λ_c\toΛ\ell^+ν$ by use of the light-cone sum rule approach with two kinds of interpolating currents. The form factors describing the decay process are obtained and used to predict the decay width. With the inclusion of up to twist-6 contributions the calculations give the decay width $Γ=(10.04\pm0.88)\times10^{-14}{GeV}$ for Chernyak-Zhitnitsky-type(CZ-type) current and $Γ=(6.45\pm1.06)\times10^{-14}{GeV}$ for Ioffe-type current. The Ioffe-type interpolating current is found to be better for th…
We study the five-body decays $μ^- \to e^- e^+ e^- ν_μ \barν_{e}$ and $τ^- \to \ell^- \ell'^+\ell'^-ν_τ\barν_{\ell}$ for $\ell, \ell'=e, μ$ within the Standard Model (SM) and in a general effective field theory description of the weak interactions at low energies. We compute the branching ratios and compare our results with two previous, mutually discrepant, SM calculations. By assuming a general structure for the weak currents we derive the expressions for the energy and angular distributions of the three charged leptons when the decaying lepton is polarized, which will be useful in precise t…
We examine lepton flavor violating (LFV) interactions for heavy right-handed neutrinos that exist in most of the standard model extensions that address dark matter (DM) and neutrino mass at the loop level. In order to probe the collider effect of these LFV interactions, we impose the assumption that the model parameters give the right values of the DM relic density and fulfill the constraints from the LFV processes $\ell_α\rightarrow\ell_βγ$ and $\ell_α\rightarrow3\ell_β$. We also investigate the possibility of probing these interactions, and hence the right-handed neutrino, at leptonic collid…
In this article, we assume the two nonets of scalar mesons below and above 1 GeV are all $\bar{q}q$ states, and study the semi-leptonic decays $B\to S\ell^-\barν_{\ell}$, $B\to S\ell^+\ell^-$ and $B\to S\barνν$ both in the standard model and in the universal extra dimension model using the $B-S$ form-factors calculated by the light-cone QCD sum rules in our previous work. We obtain the partial decay widths and decay widths, which can be confronted with the experimental data in the future to examine the natures of the scalar mesons and constrain the basic parameter in the universal extra dimens…
We explore discrimination of two types of leptonic Yukawa interactions associated with Higgs triplet, $\bar L^c_L ΔL_L$, and with $SU(2)$ singlet doubly charged scalar, $\bar e_R^c k^{++} e_R$. These interactions can be distinguished by measuring the effects of doubly charged scalar boson exchange in the $e^+ e^- \to \ell^+ ell^-$ processes at polarized electron-positron colliders. We study a forward-backward asymmetry of scattering angular distribution to estimate the sensitivity for these effects at the ILC. In addition, we investigate prospects of upper bounds on the Yukawa couplings by com…
Long-distance QCD effects in $B_{d,s}\to\ell^+\ell^-γ$ decays are analyzed. We show that the contribution of the light vector-meson resonances related to the virtual photon emission from valence quarks of the $B$-meson, which was not considered in previous analyses, strongly influences the dilepton differential distrubution. Taking into account photon emission from the $b$-quark loop, weak annihilation, and Bremsstrahlung from leptons in the final state, we give predictions for dilepton spectrum in $B_{d, s}\to \ell^+\ell^-γ$ decays within the Standard model.
The radiative corrections to the pure leptonic decay $B_c \to \ellν_{\ell}$ up-to one-loop order is presented. How to cancel the infrared divergences appearing in the loop calculations, and the radiative decay $B_c \to \ellν_{\ell}γ$ is shown precisely. It is emphasized that the radiative decay may be separated properly and may compare with measurements directly as long as the theoretical `softness' of the photon corresponds to the experimental resolutions. Furthermore with a kind of non-relativistic constituent quark model, a kind of typical long distance contributions to the radiative decays…
We present our recent results for long-distance QCD effects in the FCNC radiative leptonic decays $B\toγ\ell^+\ell^-$, $\ell=\{e,μ\}$. One encounters here two distinct types of long-distance effects: those encoded in the $B\toγ$ transition form factors induced by the $b\to q$ quark currents, and those related to the charm-loop effects. We calculate the $B\toγ$ form factors in a broad range of the momentum transfers making use of the relativisitc dispersion approach based on the constituent quark picture which has proven to provide reliable predictions for many weak-transition form factors. Con…
We investigate the TeV models for neutrino mass generation as candidate models to explain the recent 2$σ$ excess of leptonic $W^{+}W^{-}$ pair production at LHC. Several models with singly charged exotic states that may explain the excess require light masses completely excluded by LEP experiments. One possible model with new lepton doublets can fit the observation and evade all direct search bounds but with tuned Yukawa structure to satisfy lepton universality. The new exotic leptons $L^{\pm}$ decay into $L^{\pm}\to \ell^{\pm} ϕ$ where $ϕ$ is a light singlet scalar of $\cal O$(MeV) that decay…
It has been known that there exists a disagreement emerged between the determination of $|V_{ub}|$ from inclusive $B \to X_u\ellν$ decays and exclusive $B \to π\ellν$ decays. In order to solve the mismatch, we investigate the left-right (LR) mixing effects, denoted by $ξ_u$, in leptonic and semileptonic $b \to u$ decays. We find that the new interactions $(V+A)\times (V-A)$ induced via the LR mixing can explain the mismatch between the values of $|V_{ub}|$ if Re$(ξ_{u})=-(0.14 \pm 0.12)$. Furthermore, we also find that the LR mixing effects can enhance the branching fractions for $B \to τν$ an…
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…
According to heavy-meson chiral perturbation theory, the vector form factor $f_+(q^2)$ of exclusive semi-leptonic decay $B\to π\ell ν$ is closely related, at least in the soft-pion region (i.e., $q^{2} \sim (m_B-m_π)^2$), to the strong coupling $g_{B^* Bπ}$ or the normalized coupling $\hat g$. Combining the precisely measured $q^2$ spectrum of $B\to π\ell ν$ decay by the BaBar and Belle collaborations with several parametrizations of the form factor $f_+(q^2)$, we can extract these couplings from the residue of the form factor at the $B^*$ pole, which relies on an extrapolation of the form fac…
We consider the axial-vector mesons $K_1(1270)$ and $K_1(1400)$ as a mixture of two $|^3P_1\rangle$ and $|^1P_1\rangle$ states with the mixing angle $θ$ that equal to $(-34\pm 13)^\circ$. We calculate the light-front distribution amplitudes (LFDAs) and decay constant formulas for both the axial-vector mesons $K_1$ in the AdS/QCD correspondence. The transition form factors of the semileptonic $B\to K_1$ decays are derived in terms of the LFDAs for $K_1$ mesons. Using these form factors and decay constant values, the differential branching ratios of $B\to K_1 (1270, 1400) \ell^+ \ell^-$,~$\ell=μ…
Some selected topics involving photonic and leptonic rare B decays are reviewed. The interest in their measurement for the CKM phenomenology is underlined. They are also potentially interesting in searching for physics beyond the standard model. This is illustrated on the examples of the decays $B \to (K,K^*) \ell^+ \ell^-$ and $B \to (ρ, ω) γ$ by contrasting their anticipated phenomenological profiles in the standard model and some variants of supersymmetric models.
The radiative corrections to the pure leptonic decay $D_s{\longrightarrow} {\ell}{ν}_{\ell}$ up-to one-loop order is presented. We find the virtual photon loop corrections to $D_s{\longrightarrow} τ{ν}_τ$ is negative and the corresponding branching ratio is larger than $3.51\times 10^{-3}$. Considering the possible experimental resolutions, our prediction of the radiative decay $D_s{\longrightarrow} τ{ν}_τγ$ is not so large as others, and the best channel to determine the $V_{cs}$ or $f_{D_s}$ is $D_s{\longrightarrow} μ{ν}_μγ$. How to cancel the infrared divergences appearing in the loop calcu…
Considering the constraints of the lepton flavor violating (LFV) processes $μ\rightarrow 3e$ and $τ\rightarrow3μ$ on the LFV couplings $Z'\ell_{i}\ell_{j}$, in the contexts of the $E_{6}$ models, the left-right (LR) models, the "alternative" left-right (ALR) models and the 331 models, we investigate the contributions of the extra gauge boson $Z'$ to the decay rates of the processes $\ell_{i}\rightarrow\ell_{j}ν_{\ell}ν_{\ell}$, $τ\rightarrowμP $ and $P\rightarrow μe$ with $P=π^{0},η$ and $η'$. Our numerical results show that the maximal values of the branching ratios for these processes are no…
Hadronic $Zγ$ Production with QCD Corrections and Leptonic Decays
过程$p p \to Z γ+ X \to \ell^- \ell^+ γ+ X$，其中$\ell$表示轻子，被计算为$α_s$级。总的和微分截面，与接受削减施加在轻子和光子，给出了Tevatron和LHC的质心能量。在一般情况下，不变的质量和角分布简单地按比例放大的大小由QCD辐射修正，而在横向动量分布，QCD辐射修正增加与横向动量。
Flavour Changing Neutral Current decays of the $B$-meson are a very useful tool for studying possible physics scenarios beyond the Standard Model (SM), where of the many FCNC modes radiative, purely leptonic and semi-leptonic decays of the $B$-meson are relatively clean tests. Within this context the BELLE collaboration has searched for the $B \to K_1(1270) γ$ process and provided an upper bound on this decay. In this work we have used this upper bound in studying the angular coorelations for the related semi-leptonic decay mode $B \to K_1(1270) (\to ρK) \ell^+ \ell^-$, where we have used the …
We revisit the heavy quarkonium leptonic decays $ψ(nS) \to \ell^+\ell^-$ and $Υ(nS) \to \ell^+\ell^-$ using the Bethe-Salpeter method. The emphasis is on the relativistic correction. For the $ψ(1S-5S)$ decays, the relativistic effects are $22^{+3}_{-2}\%$, $34^{+5}_{-5}\%$, $41^{+6}_{-6}\%$, $52^{+11}_{-13}\%$ and $62^{+14}_{-12}\%$, respectively. For the $Υ(1S-5S)$ decays, the relativistic effects are $14^{+1}_{-2}\%$, $23^{+0}_{-3}\%$, $20^{+8}_{-2}\%$, $21^{+6}_{-7}\%$ and $28^{+2}_{-7}\%$, respectively. Thus, the relativistic corrections are large and important in heavy quarkonium leptonic…
We propose two different and complementary observables for singling out possible signals of physics beyond the standard model in the semi-leptonic decays $Λ_b \to Λ_c \ell{\bar ν}_{\ell}$, both with the $τ$ lepton and with a light lepton. The two observables are the partial decay width and a T-odd asymmetry, whose respective sensitivities to scalar and/or pseudo-scalar coupling are calculated as functions of the parameters characterizing new physics. Two different form factors are used. Three particular cases are discussed and analyzed in detail.
The radiative corrections to the pure leptonic decay $D_s{\longrightarrow} {\ell}{ν}_{\ell}$ up-to one-loop order is presented. We find the virtual photon loop corrections to $D_s{\longrightarrow} τ{ν}_τ$ is negative and the corresponding branching ratio is larger than $3.51\times 10^{-3}$. Considering the possible experimental resolutions, our prediction of the radiative decay $D_s{\longrightarrow} τ{ν}_τγ$ is not so large as others, and the best radiative channel to determine the $V_{cs}$ or $f_{D_s}$ is $D_s{\longrightarrow} μ{ν}_μγ$.
Semi-leptonic $B_s \to K \ell ν$ and $B_s \to D_s \ell ν$ decays provide an alternative $b$-decay channel to determine the CKM matrix elements $|V_{ub}|$ and $|V_{cb}|$ or to obtain $R$-ratios to investigate lepton flavor universality violations. In addition, these decays may shed further light on the discrepancies seen in the analysis of inclusive vs. exclusive decays. Using the nonperturbative methods of lattice QCD, theoretical results are obtained with good precision and full control over systematic uncertainties. This talk will highlight ongoing efforts of the $B$-physics program by the R…
The complete next-to-next-to-next-to-leading order short-distance and bound-state QCD corrections to $Υ(1S)$ leptonic decay rate $Γ(Υ(1S)\to \ell^+\ell^-)$ has been finished by Beneke {\it et al.} \cite{Beneke:2014qea}. Based on those improvements, we present a renormalization group (RG) improved pQCD prediction for $Γ(Υ(1S)\to \ell^+\ell^-)$ by applying the principle of maximum conformality (PMC). The PMC is based on RG-invariance and is designed to solve the pQCD renormalization scheme and scale ambiguities. After applying the PMC, all known-type of $β$-terms at all orders, which are control…
We consider leptonic $B^-\to \ell^- \barν_\ell$ and semileptonic $\bar B \to π\ell^- \barν_\ell$, $\bar B \to ρ\ell^- \barν_\ell$ decays and present a strategy to determine short-distance coefficients of New-Physics operators and the CKM element $|V_{ub}|$. As the leptonic channels play a central role, we illustrate this method for (pseudo)-scalar operators which may lift the helicity suppression of the corresponding transition amplitudes arising in the Standard Model. Utilising a new result by the Belle collaboration for the branching ratio of $B^-\to μ^- \barν_μ$, we explore theoretically cl…
The transitions $B_{s,d}\rightarrow \ell^+\ell^-$ (for $\ell=e, μ, τ$), although extremely suppressed within the SM, are exceptionally clean channels particularly sensitive to New Physics contributions. So far only the branching ratio for the process $B_{s}\rightarrow μ^+μ^-$ has been measured experimentally and, although the results are in agreement with the SM prediction, there is still room for NP effects. Here we provide an overview of the theoretical status of rare decays. We present strategies that can allow us to discriminate between different NP scenarios. Finally, we include a discuss…
The study of the purely leptonic decays of the ground charged vector mesons is very interesting and significant in determining the CKM matrix elements, obtaining the decay constant of vector mesons, examining the lepton flavor universality, and searching for new physics beyond the standard model. These purely leptonic decays of the ground charged vector mesons are induced by the weak interactions within the standard model, and usually have very small branching ratios, ${\cal B}(ρ^{-}{\to}{\ell}^{-}ν_{\ell})$ ${\sim}$ ${\cal O}(10^{-13})$, ${\cal B}(K^{{\ast}-}{\to}{\ell}^{-}ν_{\ell})$ ${\sim}$…
To the leading order, the radiative leptonic decays $B_c \to γ\ell \bar ν$ ($ \ell=e, μ$) are studied carefully. In the study, a non-relativistic constituent quark model and the effective Lagrangian for the heavy flavour decays are used. As a result, the branching ratios turn out to be of the orders of $10^{-5}$ for $B_c \to γμ\bar ν$ or for $B_c \to γe \bar ν$. Based on this study, we point out the decays being accessible experimentally at the future LHC, and the possibility to determine the decay constant $f_{B_c}$ through the radiative decays.
In the so-called "Yukawaon" model, the (effective) Yukawa coupling constants $Y_f^{eff}$ are given by vacuum expectation values (VEVs) of scalars $Y_f$ (Yukawaons) with $3\times 3$ components. In this brief report, we change VEV forms $<Y_f>$ in the previous paper into a unified form. Therefore, parameter fitting for quark and lepton masses and mixings is revised. Especially, we obtain predicted values of neutrino mixing $\sin^2 2θ_{13}$ and a leptonic $CP$ violating phase $δ_{CP}^\ell$ which are consistent with the observed curve in the $(\sin^2 2θ_{13}, δ_{CP}^\ell)$ reported by T2K group re…
Among the various "rare" semi-leptonic decays of $B$-mesons the $B \to K^* \ell^+ \ell^-$ mode is of special interest. This is because it has the highest branching ratio among all the semi-leptonic B decays within the SM. This channel also provides us with a very large number of possible observables, such as the Forward Backward (FB) asymmetry, lepton polarization asymmetry etc. Of special interest is the zero which the FB asymmetry has in this decay mode. In this work we have studied this zero in the most general model independent framework.
We compute two-loop corrections to the vector current matching coefficient involving two heavy quark masses. The result is applied to the computation of the $Υ(1S)$ decay width into an electron or muon pair. We complement the next-to-next-to-next-to-leading order corrections of Ref. arXiv:1401.3005 by charm quark mass effects up to second order in perturbation theory. Furthermore, we apply the formalism to $Γ(J/Ψ\to \ell^+\ell^-)$ and compare to the experimental data.
Applying the method of light-cone sum rules with photon distribution amplitudes, we compute the subleading-power correction to the radiative leptonic $B \to γ\ell ν$ decay, at next-to-leading order in QCD for the twist-two contribution and at leading order in $α_s$ for the higher-twist contributions, induced by the hadronic component of the collinear photon. The leading-twist hadronic photon effect turns out to preserve the symmetry relation between the two $B \to γ$ form factors due to the helicity conservation, however, the higher-twist hadronic photon corrections can yield symmetry-breaking…
In this work we shall derive expressions for the single and double lepton polarization asymmetries for the exclusive decay $B \to K^* \ell^+ \ell^-$, using the most general model independent effective Hamiltonian. We have conducted this study with this particular channel as it has the highest branching ratio among the various purely leptonic and semi-leptonic decay modes, making this mode particularly useful for studying physics beyond the SM. We have also analyzed the effects on these polarization asymmetries, and hence the physics underlying it, when complex phases are included in some of th…
The relatively clean theoretical probes of the Standard Model (SM), and the various theories beyond the SM, provided by radiative, semi-leptonic and (purely) leptonic decays of B-mesons have become increasingly important. Due to the large number of possible distributions in the semi-leptonic decays based on the quark level transition $b \to s \ell^+ \ell^-$ (not just the branching ratio), these transitions have become very useful. A study of the Forward-Backward asymmetries for the inclusive decay ($B \to X_s \ell^+ \ell^-$) is carried out in this paper. This study shall be performed in the SM…
We explore a possibility of optimization of the method of determination of the top quark mass from $M_{b\ell}$ distribution in semi-leptonic decays $t \to b \ellν$ at LHC and a future linear collider (LC). We discover that the systematic and statistical errors of $M_t$ determination can be diminished if considering the high moments over the distribution. In the case of LHC this allows one to reduce more than in twice the errors, and in the case of LC to approach to the precision expected at studying the threshold scan of the total cross-section $e^+e^- \to t\bar t$.
In this work, we investigate the radiative leptonic decays D_(s)^- \to γ\ell \barν(\ell = e, μ) at tree level within the non-relativistic consistuent quark model and the effective Lagrangian for the heavy flavor decays. We find that the contributions for the three Feynman diagrams are all important. With the full calculation, the decay branching ratios are of the order of 10^-5 for D_s^- \to γ\ell \barνand 10^-6 for D^- \to γ\ell \barν, respectively. These decays can be measured at B factories and future CLEO-C experiments to determine the decay constants f_D_s and f_D.
We compute corrections of order $α_s^3$ to the decay $b \to c \ell \barν$ taking into account massive charm quarks. In the on-shell scheme large three-loop corrections are found. However, in the kinetic scheme the three-loop corrections are below 1\% and thus perturbation theory is well under control. We furthermore provide results for the order $α_s^3$ corrections to $b \to u \ell \barν$ and the third-order QED corrections to the muon decay which will be important input for reducing the uncertainty of the Fermi coupling constant $G_F$.
Leptoquarks are hypothetical new particles, which couple quarks directly to leptons. They experienced a renaissance in recent years as they are prime candidates to explain the so-called \textit{flavor anomalies}, i.e. the deviations between the Standard Model predictions and measurements in $b\to s\ell^{+}\ell^{-}$ and $b\to cτν$ processes and in the anomalous magnetic moment of the muon. At the one-loop level these particles unavoidably generate effects in the purely leptonic processes like $Z\to\ell^{+}\ell^{-}$, $Z\toν\barν$, $W\to\ellν$ and $h\to\ell^{+}\ell^{-}$ and can even generate non-…
Experimental measurements of the ratios $R(D^{(*)})\equiv\frac{Γ(B\to D^{(*)}τν)}{Γ(B\to D^{(*)}\ellν)}$ ($\ell=e,μ$) show a $3.9σ$ deviation from the Standard Model prediction. In the absence of light right-handed neutrinos, a new physics contribution to $b\to cτν$ decays necessarily modifies also $b\bar b\toτ^+τ^-$ and/or $c\bar c\toτ^+τ^-$ transitions. These contributions lead to violation of lepton flavor universality in, respectively, $Υ$ and $ψ$ leptonic decays. We analyze the constraints resulting from measurements of the leptonic vector-meson decays on solutions to the $R(D^{(*)})$ puz…
Many new physics scenarios predict the existence of the extra charged gauge boson $ W'$, which can induce the charged-current (CC) non-standard neutrino interactions (NSI). We investigate the constraints on the CC NSI in model-independent fashion via considering the $ W'$ contributions to the lepton flavor violating (LFV) decays $\ell_{i}\rightarrow \ell_{j}γ$, the pure leptonic flavor conservation (FC) decays $\ell_{i}\rightarrow \ell_{j}ν_{i}\bar{ν_{j}}$, leptonic decays of charged pion meson, semileptonic $τ$ decays, and superallowed $β$ decays. We find that the constraints on the pure lept…
Leading twist light cone distribution amplitudes (LCDAs) are key ingredients in calculating various hadronic amplitudes using light cone QCD sum rules. This work concentrates on calculating the leading twist LCDAs of P-wave heavy quarkonia. Quark model wavefunctions for the ground, first and second excited states of P-wave charmonia and bottomonia have been calculated, and are used for calculating the relevant LCDAs and leptonic decay constants.
The calculation of $t\bar{t}Z$ production including leptonic decays of both $Z$ boson and top quarks via a partially or fully off-shell calculation represents a definite step forward towards a more accurate description of events whose signatures originate from $t\bar{t}Z$ production. In this talk we review two studies that represent the state of the art of theoretical modeling of $t\bar{t}Z$ production by either performing the NLO QCD calculation of the fully decayed $pp\rightarrow e^+ν_eμ^-\barν_μb\bar{b}τ^+τ^-$ process (see Ref. [1]) or matching the NLO QCD calculation of $pp\rightarrow t\ba…
In this paper and within the standard Glashow-Weinberg-Salam model of electroweak interactions, we study theoretically the leptonic decay of the $W^{-}$-boson $(W^{-}\rightarrow \ell^{-}\barν_{\ell})$ in the presence of a circularly polarized electromagnetic field and we examine the laser effect, in terms of its field strength and frequency, on the leptonic decay rate and the phenomenon of multiphoton processes. The calculations are carried out using the exact relativistic wave functions of charged particles in an electromagnetic field. It was found that the laser significantly contributed to …
We present a detailed analysis on the $B_c$ meson semi-leptonic decays, $B_c \to η_c (J/ψ) \ell ν$, up to next-to-leading order (NLO) QCD correction. We adopt the principle of maximum conformality (PMC) to set the renormalization scales for those decays. After applying the PMC scale setting, we determine the optimal renormalization scale for the $B_c\toη_c(J/ψ)$ transition form factors (TFFs). Because of the same $\{β_0\}$-terms, the optimal PMC scales at the NLO level are the same for all those TFFs, i.e. $μ_r^{\rm PMC} \approx 0.8{\rm GeV}$. We adopt a strong coupling model from the massive …
We study the radiative leptonic $B_c\to γ\ell\barν$ decays in the nonrelativistic QCD effective field theory, and consider a fast-moving photon. As a result the interactions with the heavy quarks can be integrated out, and thus we arrive at a factorization formula for the decay amplitude. We calculate not only the relevant short-distance coefficients at leading order and next-to-leading order in $α_s$, but also the nonrelativistic corrections at the order $|\bold{v}|^2$ in our analysis. We find out that the QCD corrections can sizably decrease the branching ratio and thus is of great importanc…
We present a determination of the ratio of kaon and pion leptonic decay constants in isosymmetric QCD (isoQCD), $f_K / f_π$, making use of the gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with $N_f = 2 + 1 + 1$ flavors of Wilson-clover twisted-mass quarks, including configurations close to the physical point for all dynamical flavors. The simulations are carried out at three values of the lattice spacing ranging from $\sim 0.068$ to $\sim 0.092$ fm with linear lattice size up to $L \sim 5.5$~fm. The scale is set by the PDG value of the pion decay constant, $f_π^{i…
