arXiv subjects

Xiong-Hui Cao

Publications and source records attributed to Xiong-Hui Cao.

At least 19 recordsLinked to original sources

arXiv2026

Precision Sum Rule for Nucleon Isovector Polarizabilities and the Proton-Neutron Mass Difference

The precision of the electromagnetic proton-neutron mass difference $δm_\mathrm{QED}$ extracted from the Cottingham formula hinges on a subtraction function whose low-energy normalization $\bar S(0)$ is fixed by the isovector combination of the proton and neutron polarizabilities, $(α_{E1}-β_{M1})^{p-n}$. We derive a dispersive sum rule for this combination in terms of $s$-channel photoabsorption cross sections and the product of $t$-channel $γγ\toπη/K\bar K_{I_t=1}$ and $πη/K\bar K_{I_t=1}\to N\bar N$ amplitudes, without invoking Reggeon dominance. Combining empirical pion-photoproduction multipoles with coupled-channel Muskhelishvili--Omnès representations of the scalar-isovector $πη/K\bar K$ amplitudes, we obtain $(α_{E1}-β_{M1})^{p-n}=-2.26(73)\times10^{-4}\,\mathrm{fm}^3$, fixing its sign and reducing the uncertainty by a factor of 4 compared with the previously known value. This result yields $\bar S(0)=-1.76(61)\,\mathrm{GeV}^{-2}$, leading to $δm_\mathrm{QED}=0.71^{+0.03}_{-0.06}\,\mathrm{MeV}$, substantially more precise than previous Cottingham determinations. The negative $\bar S(0)$ also provides a stringent low-energy test of Reggeon dominance in the subtraction function.

hep-ph↗

arXiv2026

Low-energy scattering of the $J/ψπ$ and $J/ψK$ system

We investigate the low-energy interactions between the charmonium state $J/ψ$ and the light pseudoscalar mesons ($π$ and $K$) within the framework of dispersion relations. We demonstrate that the symmetry-breaking terms in the chiral Lagrangian induce mixing between the bare charmonium fields, necessitating a diagonalization procedure to correctly identify the physical $J/ψ$ and $ψ'$ states. Using the resulting diagonalized Lagrangian, we construct the crossed-channel amplitudes for $J/ψJ/ψ\to {\cal P}\bar{\cal P}$ and incorporate the $ππ$ and $K\bar{K}$ rescattering effects through dispersion relations. This framework is used consistently both in the phenomenological extraction of the transition parameters from $ψ' \to J/ψππ$ and in the continuation of the crossed amplitudes to the near-threshold $J/ψ{\cal P}~({\cal P}=π,K)$ region. As a result, we determine both the scattering lengths and the effective ranges. We obtain the upper-bound estimates $a_{J/ψπ}\lesssim -0.0037$~fm and $a_{J/ψK}\lesssim -0.049$~fm, where the negative sign indicates an attractive interaction without a bound state in our convention. Our results show that the $J/ψK$ interaction is moderately enhanced relative to the pion channel, driven by explicit chiral symmetry breaking. Furthermore, a quantitative comparison of the coupled-channel mechanism, where $J/ψπ$ and $J/ψK$ couple to open-charm channels, reveals that both $J/ψπ$ and $J/ψK$ scatterings are predominantly governed by the soft-gluon exchange mechanism.

hep-ph↗

arXiv2026

Comprehensive study of axion photoproduction off the nucleon in chiral effective field theory

We calculate the amplitudes of the axion photoproduction off the nucleon, i.e., $γN \to a N$, within the framework of chiral effective field theory. Several different types of contributions are simultaneously included in our calculation, namely the nucleon exchanges up to next-to-leading order, the $aγγ$ vertex and the vector meson exchanges in the $t$-channel. We utilize the existing hadronic inputs as much as possible to fix the unknown couplings. A comprehensive study of the phenomenological discussions is then provided in this work. Different mechanisms in the $γN \to a N$ processes manifest distinct behaviors in the total and differential cross sections, which could provide useful quantities to distinguish different axion models.

hep-ph↗

arXiv2026

Dispersive analysis of the $J/ψ\toπ^0 γ^\ast$ transition form factor with $ρ$-$ω$ mixing effects

Motivated by the discrepancies noted recently between the theoretical predictions of the electromagnetic $J/ψ\to π^0 γ^*$ transition form factor and the BESIII data, we reanalyze this transition form factor using the dispersive Khuri-Treiman equations, with final-state interactions in both the direct channel and the crossed channels properly considered. This improved framework incorporates $ρ$-$ω$ mixing effects. The effect of four-pion states is evaluated through a dispersively improved vector-meson-dominance model. From this information, we propose a two-parameter fit that provides an excellent description of the BESIII data over the broad energy range from 0 to 2.8GeV. We demonstrate that the $ρπ^0$ decay mode of the $J/ψ$ is dominated by strong interaction, while the $ωπ^0$ mode is dominated by one-photon exchange. From this, we extract the relative phase between the strong and the one-virtual-photon (electromagnetic) modes in hadronic decays of $J/ψ$ as $(62 \pm 21)^{\circ}$. This could provide useful information in understanding the long-standing $ρπ$ puzzle in $J/ψ$ decays.

hep-ph↗

arXiv2026

Axion-like particle production from lepton-nucleon scattering in chiral effective theory

In this work we study the axion/axion-like particle production from the lepton-nucleon scattering in the low-energy region, i.e., the $\ell N\to \ell N a$ processes, $\ell$ being the electron or muon and $N$ the proton or neutron. We simultaneously include three different types of axion interaction couplings within the chiral effective field theory, namely the axion-nucleon-nucleon couplings $g_{aNN}$, axion-photon-photon coupling $g_{aγγ}$ and axion-photon-vector meson resonances couplings $g_{ρaγ}$ and $g_{ωaγ}$. Vast inputs from the lattice QCD and hadron phenomenological studies are used to fix the unknown couplings. The relative strengths of different axion interactions in the $\ell N\to \ell N a$ processes are then revealed. We provide detailed predictions for the differential cross sections with respect to various angles and axion energy, as well as the total cross sections in the low-energy region around production thresholds, both for the Kim-Shifman-Vainstein-Zakharov (KSVZ) and Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) axion models.

hep-ph↗

arXiv2025

Renormalization of chiral perturbation theory with spinless matter field in curved spacetime

We generalize chiral perturbation theory with spinless matter fields in the fundamental representation of ${\rm SU}(N)$ to curved spacetime in the presence of an external gravitational field. This work is motivated by recent interest in investigating energy-momentum tensor matrix elements of matter fields. The complete chiral Lagrangian is constructed, including both minimal extensions from flat spacetime and new curvature-induced terms, up to the next-to-next-to-leading order in the chiral expansion, $\mathcal{O}(p^3)$. We perform a systematic one-loop renormalization of the generating functional using the background field method combined with the heat-kernel technique, and explicitly compute the resulting ultraviolet divergences.

hep-ph↗

arXiv2025

Gravitational form factors of pions, kaons and nucleons from dispersion relations

The gravitational form factors of pions, kaons and the nucleons are investigated by employing modern dispersive techniques and chiral perturbation theory. We determine the gravitational form factors of pions and kaons, extending our analysis to explore the pion mass dependence of these form factors at several unphysical pion masses up to 391 MeV, for which lattice results exist for the meson-meson scattering phase shifts. We also review our analysis on the nucleon gravitational form factors at the physical pion mass, and then systematically calculate various three-dimensional spatial and two-dimensional transverse density distributions for the nucleons. These results provide new insights into the mass distribution inside nucleons. As a by-product, we match our dispersion relation results and those obtained from chiral perturbation theory with external gravitational source at the next-to-next-to-leading order, yielding values for the low-energy constants $c_8=-4.28_{-0.38}^{+0.37} ~\mathrm{GeV}^{-1}$ and $c_9=-0.68_{-0.05}^{+0.06} ~\mathrm{GeV}^{-1}$. These results offer a robust benchmark for future experimental and theoretical studies.

hep-ph↗

arXiv2025

Rigorous Roy-Steiner equation analysis of $πK$ scattering at unphysical quark masses

We perform a rigorous analysis of the $πK$ scattering at an unphysical pion mass 391 MeV using the Roy-Steiner equations, which satisfy unitarity, analyticity and crossing symmetry, for the first time. Stable solutions of the Roy-Steiner equations with different quantum numbers of isospin and angular momentum are obtained in the elastic energy region, by taking inputs from the $πK$ lattice data in the inelastic region, the lattice data from the crossed $ππ\to K\bar{K}$ channels, the masses of $f_0(500)$ and $K^*$ at the same pion mass from previous study, and the Regge model. Predictions on the elastic $πK$ scattering phase shifts and the $K_0^*(700)$ pole content are made. Contrary to the virtual pole scenario obtained using the $K$-matrix method in the literature, we find that lightest strange scalar meson $K_0^*(700)$ remains a broad resonance at $m_π=391$ MeV. The cross-channel dynamics is found to play a crucial role in deriving the proper pole position.

hep-ph↗

arXiv2025

Revisiting Roy-Steiner-equation analysis of pion-kaon scattering from lattice QCD data

A comprehensive analysis of $πK\rightarrow πK$ and $ππ\rightarrow K\bar K$ amplitudes at large unphysical pion mass for all important partial waves is presented. A set of crossing-symmetric partial-wave hyperbolic dispersion relations is used to describe lattice QCD data at $m_π=391$ MeV. In the present analysis, the amplitudes for the $S$- and $P$-waves are formulated by combining the constraints of analyticity, unitarity, and crossing symmetry, fulfilling Roy-Steiner-type equations. We use these results to investigate the low-lying strange-meson resonances and resolve the instability problem tied to analytic continuation in prior lattice QCD studies based on the $K$-matrix formalism. At $m_π=391$ MeV, the rigorous Roy-Steiner-type equation approach allows us to determine the $S$-wave scattering lengths, $m_πa_0^{1/2}=\left(0.92_{-0.28}^{+0.06}\right)$, $m_πa_0^{3/2}=-\left(0.32_{-0.02}^{+0.05}\right)$, and the $κ$ (also known as $K_0^*(700)$) pole position, $\sqrt{s_κ}=\left(966_{-24}^{+41}-i 198_{-17}^{+38}\right)$ MeV. We also provide a detailed analysis of the complex validity domain of the Roy-Steiner-type equations.

hep-ph↗

arXiv2025

Discontinuity calculus and applications to two-body coupled-channel scattering

We present a novel method, termed discontinuity calculus, for computing discontinuities of complex functions. This framework enables a systematic investigation of both analytic continuation and the topological structure of Riemann surfaces. We apply this calculus to analyze the analytic continuation of partial-wave amplitudes in two-body coupled-channel scattering problems and discuss their uniformization of the corresponding Riemann surfaces. This methodology offers new perspectives and tools for analyzing coupled-channel scattering problems in quantum scattering theory.

hep-ph↗

arXiv2025

Dispersive Determination of Nucleon Gravitational Form Factors

Being closely connected to the origin of the nucleon mass, the gravitational form factors of the nucleon have attracted significant attention in recent years. We present the first model-independent determinations of the gravitational form factors of the pion and nucleon at the physical pion mass, using a data-driven dispersive approach. The so-called "last global unknown property" of the nucleon, the $D$-term, is determined to be $-3.38^{+0.34}_{-0.35}$. The root mean square radius of the scalar trace density inside the nucleon is determined to be $(0.97 \pm0.03)~\text{fm}$. Notably, this value is larger than the proton charge radius, suggesting a modern structural view of the nucleon where gluons, responsible for most of the nucleon mass, are distributed over a larger spatial region than quarks, which dominate the charge distribution, indicating that the radius of the trace density may be regarded as a confinement radius. We also predict the nucleon angular momentum and mechanical radii, providing further insights into the intricate internal structure of the nucleon.

hep-ph↗

arXiv2025

Double pion photoproduction off nucleons in covariant chiral perturbation theory

The double pion photoproduction off nucleons near threshold is analyzed in a covariant baryon chiral perturbation theory up to next to leading order, where the $Δ(1232)$, $N^*(1400)$ and $ρ(770)$ resonances are included as explicit degrees of freedom. For the process $γp \to π^+ π^0 n$, the chiral results of total cross sections, invariant-mass distributions and beam-helicity asymmetry are in good agreement with the experimental data within uncertainties. For the process $γp \to π^0 π^0 p$, the prediction of total cross section deviates from the existing experimental data. Once the final-state interaction of $ππ$ in the isoscalar S-wave channel is taken into account, a good description of the cross section is achieved. The effect of the Roper resonance always turns out be negligible, and hence can be thrown away in future study of this process.

hep-ph↗

arXiv2024

Photoproduction of the $X(3872)$ beyond vector meson dominance: the open-charm coupled-channel mechanism

Hidden-charm exotic hadrons will be searched for and investigated at future electron-ion colliders. For instance, the $X(3872)$ can be produced through the exclusive process $γp\to X(3872)p$. The vector meson dominance model has been commonly employed in estimating the cross sections of such processes. However, the coupled-channel production mechanism through open-charm meson-baryon intermediate states may play a crucial role. To assess the significance of such contributions, we estimate the cross section of the $γp\to X(3872)p$ reaction assuming the coupled-channel mechanism. For energies near the threshold, the total cross section is predicted to be of tens of nanobarns for $γp\to X(3872)p$, which can be measured at future experimental facilities. Furthermore, the open-charm coupled-channel mechanism leads to a distinct line shape of the total cross section that can be utilized to reveal the production dynamics.

hep-ph↗

arXiv2024

Nucleon electric polarizabilities and nucleon-pion scattering at physical pion mass

We present a lattice QCD calculation of the nucleon electric polarizabilities at the physical pion mass. Our findings reveal the substantial contributions of the $Nπ$ states to these polarizabilities. Without considering these contributions, the lattice results fall significantly below the experimental values, consistent with previous lattice studies. This observation has motivated us to compute both the parity-negative $Nπ$ scattering up to a nucleon momentum of $\sim0.5$ GeV in the center-of-mass frame and corresponding $Nγ^*\to Nπ$ matrix elements using lattice QCD. Our results confirm that incorporating dynamic $Nπ$ contributions is crucial for a reliable determination of the polarizabilities from lattice QCD. This methodology lays the groundwork for future lattice QCD investigations into various other polarizabilities.

hep-lat↗

arXiv2024

$σ$ exchange in the one-boson exchange model involving the ground state octet baryons

Based on the one-boson-exchange framework that the $σ$ meson serves as an effective parameterization for the correlated scalar-isoscalar $ππ$ interaction, we calculate the coupling constants of the $σ$ to the $\frac{1}{2}^+$ ground state light baryon octet ${\mathbb B}$ by matching the amplitude of ${\mathbb B}\bar{\mathbb B}\toππ\to\bar{\mathbb B}{\mathbb B}$ to that of ${\mathbb B}\bar{\mathbb B}\toσ\to\bar{\mathbb B}{\mathbb B}$. The former is calculated using a dispersion relation, supplemented with chiral perturbation theory results for the ${\mathbb B}{\mathbb B}ππ$ couplings and the Muskhelishvili-Omn\` es representation for the $ππ$ rescattering. Explicitly, the coupling constants are obtained as $g_{NNσ}=8.7_{-1.9}^{+1.7}$, $g_{ΣΣσ}=3.5_{-1.3}^{+1.8}$, $g_{ΞΞσ}=2.5_{-1.4}^{+1.5}$, and $g_{ΛΛσ}=6.8_{-1.7}^{+1.5}$. These coupling constants can be used in the one-boson-exchange model calculations of the interaction of light baryons with other hadrons.

hep-ph↗

arXiv2023

Roy equation analyses of $ππ$ scatterings at unphysical pion masses

An extended Roy equation including a bound state pole is used to study $ππ$ scatterings at unphysical large pion masses when $σ$ becomes a bound state in one situation and stays as a broad resonance in the other case. The coupled integral equations at large pion masses are solved by taking the lattice driving terms and the Regge amplitudes as inputs. Relying on the solutions of Roy equations that respect unitarity, analyticity and crossing symmetry, we give predictions to the phase shifts with $IJ=00,11,20$ in the elastic energy region. We then perform analytic continuation into the complex $s$ plane to search for various poles, all of which are inside the validity domain of the Roy equation. This is the first time that lattice data at unphysical large pion masses are analyzed within the rigorous Roy equation method.

hep-ph↗

arXiv2022

A possible subthreshold pole in $S_{11}$ channel from $πN$ Roy-Steiner equation analyses

The hyperbolic version of Roy-Steiner equation describing low energy $πN$ scatterings, with larger analyticity domain in the complex $s$ plane is solved. The numerical results on phase shifts of low partial waves are in agreement with that of Hoferichter et al. [Phys. Rept. 625 (2016) 1]. A subthreshold pole in $S_{11}$ channel is found located at $\sqrt{s}=(918 \pm 3)-i (163 \pm 9)$~MeV.

hep-ph↗

arXiv2022

Radiative Correction to Lepton Proton Scatterings in Manifestly Lorentz-Invariant Chiral Perturbation Theory

Manifestly Lorentz-invariant baryon chiral perturbation theory is used to calculate the radiative correction of low energy elastic lepton proton scatterings. Corrections of differential cross section and charge asymmetry are given at chiral next-to-leading order $(\mathcal{O}(p^2))$ with a nonzero lepton mass, which are infrared and ultraviolet finite. The results are basically consistent with previous predictions based on hadron model calculation, but they are somewhat different from calculations based on heavy baryon chiral perturbation theory, especially in charge asymmetry.

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