arXiv subjects

Fangcheng He

Publications and source records attributed to Fangcheng He.

29 records · Page 2Linked to original sources

arXiv2022

Generalized parton distributions of sea quarks in the proton from nonlocal chiral effective theory

We calculate the spin-averaged generalized parton distributions (GPDs) of sea quarks in the proton at zero skewness from nonlocal covariant chiral effective theory, including one-loop contributions from intermediate states with pseudoscalar mesons and octet and decuplet baryons. A relativistic regulator is generated from the nonlocal Lagrangian where a gauge link is introduced to guarantee local gauge invariance, with additional diagrams from the expansion of the gauge link ensuring conservation of electric charge and strangeness. Flavor asymmetries for sea quarks at zero and finite momentum transfer, as well as strange form factors, are obtained from the calculated GPDs, and results compared with phenomenological extractions and lattice QCD.

hep-ph↗

arXiv2022

Nucleon form factors and parton distributions in nonlocal chiral effective theory

We present a review of recent applications of nonlocal chiral effective theory to hadron structure studies. Starting from a nonlocal meson--baryon effective chiral Lagrangian, we show how the introduction of a correlation function representing the finite extent of hadrons regularizes the meson loop integrals and introduces momentum dependence in vertex form factors in a gauge invariant manner. We apply the framework to the calculation of nucleon electromagnetic form factors, unpolarized and polarized parton distributions, as well as transverse momentum dependent distributions and generalized parton distributions. Assuming that the nonlocal behavior is a general property of all interactions, we also discuss the application to the lepton anomalous magnetic moment in nonlocal QED.

hep-ph↗

arXiv2022

Helicity-dependent distribution of strange quarks in the proton from nonlocal chiral effective theory

The helicity-dependent strange quark distribution in the proton, $Δs$, is calculated in a nonlocal chiral SU(3) effective field theory. The hadronic proton to meson plus octet or decuplet baryon splitting functions are derived at the one-loop level, with loop integrals rendered finite by correlation functions introduced in the nonlocal Lagrangian. Within the convolution framework, the proton strange helicity distribution is obtained using spin-flavor symmetry to constrain the input valence quark distributions in the hadronic intermediate states. The polarized strange quark distribution is found to be quite small, with the lowest moment of $Δs$ negative, but consistent with recent global QCD analyses.

hep-ph↗

arXiv2021

Renormalization constants of overlap quark bilinear operators from RI/MOM and RI/SMOM scheme

We calculate the renormalization constants (RCs) of vector, axial, vector scalar, pseudoscalar and tensor quark operators of the overlap valence fermion, on the 11 gauge ensembles with dynamical fermion using either Domain wall fermion~(DWF) action orHighly improved stagger quark~(HISQ) action at lattice spacings from 0.04 fm to 0.20 fm. We find the results under the $\overline{\text{MS}}$ scheme using either the RI/MOM or RI/SMOM scheme are consistent with each other, once the proper $a^2p^2$ extrapolation is applied and the systematic uncertainties are estimated cautiously. Our results with different gauge and fermion actions also indicate that the RCs are majorly dependent on the lattice spacing (as the inverse of UV cut-off) rather than the bare gauge coupling used by the gauge action.

hep-lat↗

arXiv2021

Chiral extrapolation of the charged-pion magnetic polarizability with Padé approximant

The background magnetic-field formalism of Lattice QCD has been used recently to calculate the magnetic polarizability of the charged pion. These $n_f = 2 + 1$ numerical simulations are electro-quenched, such that the virtual sea-quarks of the QCD vacuum do not interact with the background field. To understand the impact of this, we draw on partially quenched chiral perturbation theory. In this case, the leading term proportional to $1/M_π$ arises at tree level from $\mathcal{L}_4$. To describe the results from lattice QCD, while maintaining the exact leading terms of chiral perturbation theory, we introduce a Padé approximant designed to reproduce the slow variation observed in the lattice QCD results. Two-loop contributions are introduced to assess the systematic uncertainty associated with higher-order terms of the expansion. Upon extrapolation, the magnetic polarizability of the charged pion at the physical pion mass is found to be $β_{π^\pm}=-1.70\,(14)_{\rm stat}(25)_{\rm syst}\times 10^{-4}$ fm$^3$, in good agreement with the recent experimental measurement.

nucl-th↗

arXiv2021

A Demonstration of Hadron Mass Origin from QCD Trace Anomaly

Quantum chromodynamics (QCD) claims that the major source of the nucleon invariant mass is not the Higgs mechanism but the trace anomaly in QCD energy momentum tensor. Although experimental and theoretical results support such conclusion, a direct demonstration is still absent. We present the first Lattice QCD calculation of the quark and gluon trace anomaly contributions to the hadron masses, using the overlap fermion on the 2+1 flavor dynamical Domain wall quark ensemble at $m_π=340$ MeV and lattice spacing $a=$0.1105 fm. The result shows that the gluon trace anomaly contributes to most of the nucleon mass, and the contribution in the pion state is smaller than that in others nearly by a factor $\sim$10 since the gluon trace anomaly density inside pion is different from the other hadrons and the magnitude is much smaller. The gluon trace anomaly coefficient $β/g^3=-0.056(6)$ we obtained is consistent with its regularization independent leading order value $(-11+\frac{2N_f}{3})/(4π)^2$ perfectly.

hep-lat↗

arXiv2020

Chiral extrapolation of the magnetic polarizability of the neutral pion

The magnetic polarizability of the neutral pion has been calculated in the background magnetic-field formalism of Lattice QCD. In this investigation, the chiral extrapolation of these lattice results is considered in a formalism preserving the exact leading nonanalytic terms of chiral perturbation theory. The $n_f = 2 + 1$ numerical simulations are electro-quenched, such that the virtual sea-quarks of the QCD vacuum do not interact with the background field. To understand the impact of this, we draw on partially quenched chiral perturbation theory and identify the leading contributions of quark-flow connected and disconnected diagrams. While electro-quenching does not impact the leading-loop contribution to the magnetic polarizability, the loops which generate the leading term have yet to be considered in lattice QCD simulations. Lattice QCD results are used to constrain the analytic terms in the chiral expansion and supplementing those with the two-loop result from chiral perturbation theory enables an evaluation of the polarizability at the physical quark mass. The resulting magnetic polarizability of the neutral pion is $β_{π^0}=3.44(19)^{\rm stat}(37)^{\rm syst}\times 10^{-4}$ fm$^3$, which lies just above the $1 σ$ error bound of the experimental measurement.

nucl-th↗

arXiv2019

Sivers distribution functions of sea quark in proton with chiral Lagrangian

We propose a mechanism for the Sivers distribution function in proton with chiral Lagrangian. By introducing the gauge link of the vector meson, the transverse momentum dependent distribution of a pion in the nucleon is re-defined which is locally $SU(2)_V$ invariant as the Lagrangian. The eikonal propagator is generated from the gauge link and this scenario is proved to be equivalent to the final state interaction. By combining the calculated splitting function and the valence $\bar{q}$ distribution in $π$ from the recent fit, the sea quark Sivers function in proton is obtained. We find reasonable numerical results for the first momentum $xΔ^Nf_{\bar{q}}^{(1)}(x)$ without any fine tuning of the free parameters.

hep-ph↗

arXiv2019

Pauli form factors of electron and muon in nonlocal quantum electrodynamics

Pauli form factors of electron and muon are studied in nonlocal quantum electrodynamics. We calculate one loop QED correction to their Pauli form factors. The relativistic regulator is generated by the correlation function in the nonlocal interaction. The cut-off parameter $Λ$ in the regulator is determined to get the consistent anomalous magnetic moments of electron and muon at the same level as local QED. When momentum transfer is large, there exists obvious difference between nonlocal and local QED.

hep-ph↗

arXiv2018

Strange form factors of nucleon with nonlocal chiral effective Lagrangian

The strange form factors of nucleon are studied with the nonlocal chiral effective Lagrangian. One loop contributions from both octet and decuplet intermediate states are included. The relativistic regulator is obtained by the nonlocal Lagrangian where the gauge link is introduced to guarantee the local gauge symmetry. With the kaon loop, the calculated charge form factor is positive, while the magnetic form factor is negative. The strange magnetic moment is $-0.041^{+0.012}_{-0.014}$ with $Λ=0.9 \pm 0.1$ determined from the nucleon electromagnetic form factors. Our results are comparable with the recent lattice simulation.

hep-ph↗

arXiv2017

Nucleon electromagnetic form factors with non-local chiral effective Lagrangian

The relativistic version of finite-range-regularisation is proposed. The covariant regulator is generated from the nonlocal Lagrangian. This nonlocal interaction is gauge invariant and is applied to study the nucleon electromagnetic form factors at momentum transfer up to 2 GeV$^2$. Both octet and decuplet intermediate states are included in the one loop calculation. Using a dipole regulator with $Λ$ around 0.85 GeV, the obtained form factors, electromagnetic radii as well as the ratios of the form factors are all comparable with the experimental data. This successful application of chiral effective Lagrangian to relatively large momentum transfer make it possible to further investigation of hadron quantities at high $Q^2$.

nucl-th↗