arXiv subjects

Yong-Kang Huang

Publications and source records attributed to Yong-Kang Huang.

13 recordsLinked to original sources

arXiv2026

Enhanced Three-Particle Contribution to Electroweak Penguin $B$-Meson Decays

We compute for the first time the subleading twist correction to the exclusive rare $b \to \left \{s, d \right \} \ell^{+} \ell^{-}$ decays from the three-particle $B$-meson distribution amplitude at next-to-leading order accuracy by employing the soft-collinear effective theory. This constitutes the last missing ingredient for the complete factorization analysis of the hadronic matrix element of the weak effective Hamiltonian at leading power in the heavy quark expansion. Incorporating further a variety of the next-to-next-to-leading-order QCD corrections to the spectator-scattering amplitude and the weak annihilation topology, we then present the improved field-theoretic predictions for phenomenologically interesting observables in the electroweak penguin $B \to \left \{K, π\right \} \ell^{+} \ell^{-}$ decays.

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arXiv2026

SCET sum rules for $B\to D_1(2420)$ and $B\to D_1'(2430)$ form factors at next-to-leading order

We present the first calculation of the $B \to D_1(2420)$ and $B \to D'_1(2430)$ transition form factors at ${\cal O}(α_s)$ using light-cone sum rules within the framework of soft-collinear effective theory (SCET). We first match the QCD transition currents onto ${\rm SCET_I}$ and then factorize the corresponding vacuum-to-$B$-meson correlation functions in ${\rm SCET_{II}}$. The resulting factorization formulae are used to construct the leading-power sum rules for the effective SCET form factors $ξ^R_{\parallel/\perp}$ and $Ξ^R_{\parallel/\perp}$ ($R=D_1,D'_1$). In particular, we calculate the additional longitudinal form factor $ξ^R_{\parallel,m_c}$ induced by the finite charm-quark mass, whose contribution depends only on the $B$-meson light-cone distribution amplitude $ϕ_B^+(ω,μ)$. To disentangle the mixed $D_1$ and $D'_1$ states, we introduce dedicated combinations of interpolating currents, with their decay constants determined via the equations of motion. To isolate the orbitally excited states from ground-state contamination, we subtract the ground-state contribution from the total sum rules and examine the stability of the resulting sum rules. Furthermore, the $q^2$-dependence of the physical form factors is extrapolated over the full kinematic region using the Bourrely--Caprini--Lellouch parameterization. Finally, we provide phenomenological predictions for the branching fractions, differential decay widths, and lepton flavor universality ratios. Numerically, we obtain $R(D_1) = 0.070^{+0.028}_{-0.018}$ and $R(D'_1) = 0.159^{+0.032}_{-0.025}$, which can be confronted with the future measurements at Belle~II and LHCb.

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arXiv2026

Next-to-Leading Order QCD Corrections to $Λ_b \to p $ Form Factors from Light-Cone Sum Rules

In this study, we compute the radiative corrections to the $Λ_b \to p$ transition form factors at next-to-leading logarithmic accuracy, employing the framework of QCD light-cone sum rules with the light-cone distribution amplitudes of the $Λ_b$ baryon. The factorization formulae of the vacuum-to-$Λ_b$ correlation function, constructed from the interpolating current for the proton, are derived at leading power in $m_p / m_{Λ_b}$, using the method of regions. With our specific choice of interpolating current, only the twist-4 distribution amplitude of the $Λ_b$ baryon contributes to the form factors. Numerically, we find that the next-to-leading order QCD perturbative corrections reduce the tree-level form factors to approximately 65$\%$ of their original value, with the next-to-leading-order jet function providing the dominant contribution. In the large-energy limit ($E_p \to \infty$), the form factors exhibit a clear $1/E_p^3$ scaling, consistent with the expected power-counting behavior. By applying the $z$-series parameterization to perform a combined fit of the form factors from our results and available lattice QCD simulations, we further investigate the decay rate of $Λ_b \to p \ell^- \barν_{\ell}$ and extract the CKM matrix element $|V_{ub}| = (3.33\pm 0.43 ) \times 10^{-3}$.

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arXiv2026

Two-Loop Renormalization-Group Evolution for the Nucleon Distribution Amplitude

We determine for the first time the two-loop renormalization-group (RG) equation for the nucleon light-cone distribution amplitude, which constitutes the last missing ingredient for the complete next-to-leading-logarithmic corrections to the nucleon form factors in the hard-collinear factorization framework. Applying the conformal expansion for this fundamental nucleon distribution amplitude then enables us to construct an analytic solution that captures the desired scale dependence of phenomenologically interesting series coefficients. Importantly, the two-loop RG evolutions of these central hadronic quantities can bring about noticeable impacts on the corresponding leading-logarithmic results for three sample models of the nucleon distribution amplitude.

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arXiv2025

Next-to-Next-to-Leading-Order Corrections to the $B \to π$ Form Factors from Light-Cone Sum Rules

By incorporating the available leading-power results at $\mathcal{O}(α_s)$ and next-to-leading-power corrections at tree level, we improve the precision of the theoretical predictions for $B\toπ$ form factors to the $\mathcal{O}(α_s^2β_0)$ level in the large-recoil region using the light-cone sum rule approach with $B$-meson light-cone distribution amplitudes. We find that the QCD corrections at $\mathcal{O}(α_s^2β_0)$ contribute approximately $+6.1\%$ compared to the tree-level result. Combining the light-cone sum rule predictions in the large-recoil region, lattice QCD results in the small-recoil region, we perform a combined fit for the $B\toπ$ form factors across the full kinematic range. Utilizing these form factors, we calculate the branching ratios, lepton-flavor-universality ratio $R_π$, forward-backward asymmetry $\mathcal{A}_{\rm FB}$, flat term $\mathcal{F}_{\rm H}$ and polarization asymmetry $\mathcal{A}_{\rm λ_\ell}$ of $B\toπμ\barν_μ$ and $B\toπτ\barν_τ$ decays. Using the experimentally measured $q^2$-binned differential branching ratios of $B\toπμ\barν_μ$ decay as input, employing the Bourrely-Caprini-Lellouch parametrization, we extract the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}| = 3.73(14) \times 10^{-3}$.

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arXiv2024

Lepton-flavor violation in the left-right supersymmetric standard model

In the Standard Model (SM), the charged lepton-flavor violation (CLFV) processes are forbidden, so the observation of CLFV represents a clear signal of new physics that goes beyond the Standard Model. In this work, we focus on the CLFV processes $l_{j}^{-}\to l_{i}^{-}γ$ and $l_{j}^{-}\to l_{i}^{-}l_{i}^{-}l_{i}^{+}$ in LRSSM. Considering the constraints of the updated experimental datas, the numerical results show that the new contributions of $SU{{\left( 2 \right)}_{R}}$ gauge interaction and a large number of other new particles, such as ${{Z}^{'}}$ boson, double-charged Higgs-bosons in LRSSM can make significant contributions to the CLFV processes $l_{j}^{-}\to l_{i}^{-}γ$ and $l_{j}^{-}\to l_{i}^{-}l_{i}^{-}l_{i}^{+}$, which is much different from the ones predicted in other SUSY models. This work provide a theoretical base for finding the LFV phenomena in new physics.

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arXiv2024

Next-to-Leading-Order QCD Predictions for the Nucleon Form Factors

We accomplish for the first time the next-to-leading-order QCD computations of the leading-twist contributions to the Dirac form factors of both the proton and the neutron by applying the hard-collinear factorization theorem rigorously. The resulting predictions for these baryon form factors indicate that the one-loop perturbative corrections to the hard-gluon-exchange contributions are numerically substantial for a wide range of momentum transfers accessible in the current and forthcoming collider experiments. Including further the (formally) power-suppressed soft contributions due to the celebrated Feynman mechanism, we then perform the state-of-the-art analysis of the Dirac electromagnetic nucleon form factors from first field-theoretical principles, thus allowing for the most robust determinations of the nucleon distribution amplitudes from the direct comparison with the experimental measurements.

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arXiv2024

Next-to-Leading-Order Weak Annihilation Correction to Rare $B \to \left \{K, π\right \} \ell^{+} \ell^{-}$ Decays

We accomplish for the first time the next-to-leading-order computation of the weak annihilation contribution to the exclusive electroweak penguin decays $B \to \left \{K, π\right \} \ell^{+} \ell^{-}$ with an energetic light-flavour meson, which is an essential missing piece of the complete QCD correction to the matrix elements of hadronic operators in the weak effective Hamiltonian. Both the hard functions and the jet functions in the perturbative factorization formulae from the short-distance fluctuations at the two distinct scales $m_b$ and $\sqrt{m_b \, Λ}$ are determined at ${\cal O}(α_s)$ with the soft-collinear factorization technique. We then demonstrate that the one-loop weak annihilation correction can bring about the noticeable impacts on theory predictions for the CP asymmetries and the isospin asymmetry in the $B \to π\ell^{+} \ell^{-}$ decays.

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arXiv2023

Renormalization-Group Evolution for the Bottom-Meson Soft Function

We determine for the first time the renormalization-group (RG) evolution equation for the $B$-meson soft function dictating the non-perturbative strong interaction dynamics of the long-distance penguin contributions to the exclusive $b \to q \ell^{+} \ell^{-}$ and $b \to q γ$ decays. The distinctive feature of the ultraviolet renormalization of this fundamental distribution amplitude consists in the novel pattern of mixing positive into negative support for an arbitrary initial condition. The exact solution to this integro-differential RG evolution equation of the bottom-meson soft function is then derived with the Laplace transform technique, allowing for the model-independent extraction of the desired asymptotic behaviour at large/small partonic momenta.

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arXiv2023

Complete analysis on QED corrections to $B_{q}\, \to\, τ^+\, τ^-$

Motivated by a dynamical enhancement of the electromagnetic corrections by a power of $Λ_{\mathrm{QCD}}/m_b$ in $B_{d,s}\, \to\, μ^+\, μ^-$ at next-to-leading order (NLO), we extend the QED factorization effects on the leptonic $B$ meson decays with light muon leptons to tauonic final states, $B_{d,s} \, \to\, τ^+\, τ^-$, using soft-collinear effective theory (SCET). This extension is necessary owing to the appearance of the large $τ$ mass, which will lead to different power counting in SCET and also different results. We provide a complete NLO electromagnetic corrections to $B_{d,s} \, \to\, τ^+\, τ^-$, which include hard functions and hard-collinear functions below the bottom quark mass scale $μ_b$. The power enhanced electromagnetic effects from hard-collinear contributions on $B_{d,s}\, \to\, μ^+\, μ^-$ discussed before also exist in $B_{d,s} \, \to\, τ^+\, τ^-$. However the logarithm term arising from contributions of hard-collinear photon and lepton virtualities for $B_{d,s}\, \to\, τ^+\, τ^-$ is not large as it is in muon case due to the hard-collinear scale of $τ$ mass, which lead to only approximately $0.04\%$ QED corrections to the branching fraction of $B_{d,s} \, \to\, τ^+\, τ^-$ compared with overall reduction about $0.5\%$ in $B_{d,s}\, \to\, μ^+\, μ^-$.

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arXiv2023

Shedding New Light on ${\cal R} (D_{(s)}^{(\ast)} )$ and $|V_{cb}|$ from Semileptonic $\bar B_{(s)} \to D_{(s)}^{(\ast)} \ell \bar ν_{\ell}$ Decays

We compute for the first time the next-to-leading-order QCD corrections to the $\bar B_{(s)} \to D_{(s)}^{(\ast)}$ form factors at large hadronic recoil. Both the charm-quark-mass and the strange-quark-mass dependent pieces can generate the leading-power contributions to these form factors. Including further various power-suppressed contributions, we perform the combined fits of the considered form factors to both our large-recoil theory predictions and the lattice QCD results, thus improving upon the previous determinations of the lepton-flavour-universality ratios ${\cal R} (D^{(\ast)})$ significantly.

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arXiv2022

Precision calculations of $B_{d, s} \to π, K$ decay form factors in soft-collinear effective theory

We improve QCD calculations of the $B_{d, s} \to π, K$ form factors at large hadronic recoil by implementing the next-to-leading-logarithmic resummation for the obtained leading-power light-cone sum rules in the soft-collinear effective theory (SCET) framework. Additionally, we endeavour to investigate a variety of the subleading-power contributions to these heavy-to-light form factors at ${\cal O}(α_s^0)$, by including the higher-order terms in the heavy-quark expansion of the hard-collinear quark propagator, by evaluating the desired effective matrix element of the next-to-leading-order term in the ${\rm SCET_{I}}$ representation of the weak transition current, by taking into account the off-light-cone contributions of the two-body heavy-quark effective theory matrix elements as well as the three-particle higher-twist corrections from the subleading bottom-meson light-cone distribution amplitudes, and by computing the twist-five and twist-six four-body higher-twist effects with the aid of the factorization approximation. Having at our disposal the SCET sum rules for the exclusive $B$-meson decay form factors, we further explore in detail numerical implications of the newly computed subleading-power corrections by employing the three-parameter model for both the leading-twist and higher-twist $B$-meson distribution amplitudes. Taking advantage of the customary Bourrely-Caprini-Lellouch parametrization for the semileptonic $B_{d, s} \to π, K$ form factors, we then determine the correlated numerical results for the interesting series coefficients, by carrying out the simultaneous fit of the exclusive $B$-meson decay form factors to both the achieved SCET sum rule predictions and the available lattice QCD results.

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arXiv2021

Higher-twist corrections to $D\toπ,K$ form factors from light-cone sum rules

We calculate the $D\to P$ transition form factors within the framework of the light-cone QCD sum rules (LCSR) with the $D$-meson light-cone distribution amplitudes (LCDAs). The next-to-leading power (NLP) corrections to the vacuum-to-$D$-meson correlation function are considered, and the NLP corrections from the high-twist $D$-meson LCDAs and the SU(3) breaking effect from strange quark mass are investigated. Adopting the exponential model of the $D$-meson LCDAs,the predicted SU(3) flavor symmetry breaking effects are $R_{SU(3)}^{+,0}=1.12$ and $R_{SU(3)}^{T}=1.39$, respectively, which confirms the results from LCSR with pion LCDA. The numerical predictions of the form factors show that the contribution from two-particle higher-twist contributions is of great importance and the uncertainties are dominated by the inverse moment of $ϕ_D^+(ω, μ)$. With the obtained form factors, the predicted Cabibbo-Kobayashi-Maskawa (CKM) matrix elements are $|V_{cd}|=0.151\,{}^{+0.091}_{-0.043} \big |_{\rm th.}\,{}^{+0.017}_{-0.02} \big |_{\rm exp.}$ and $|V_{cs}|=0.89\,{}^{+0.467}_{-0.234} \big |_{\rm th.}\,{}^{+0.008}_{-0.008} \big |_{\rm exp.}$.

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