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Xiangdong Ji

Publications and source records attributed to Xiangdong Ji.

302 records · Page 17Linked to original sources
arXiv1995

BREAKUP OF HADRON MASSES AND ENERGY-MOMENTUM TENSOR OF QCD

Hadron masses are shown to be separable in QCD into contributions of quark and gluon kinetic and potential energies, quark masses, and the trace anomaly. The separation is based on a study of the structure of the QCD energy-momentum tensor and its matrix elements in hadron states. The paper contains two parts. In the first part, a detailed discussion of the renormalization properties of the energy-momentum tensor is given. In the second part, a mass separation formula is derived and then applied to the nucleon, pion, and the QCD vacuum. Implications of the results on hadron structure and non-perturbative QCD dynamics are discussed.

hep-ph↗
arXiv1995

SOFFER'S INEQUALITY

Various issues surrounding a recently proposed inequality among twist-two quark distributions in the nucleon are discussed. We provide a rigorous derivation of the inequality in QCD, including radiative corrections and scale dependence. We also give a more heuristic, but more physical derivation, from which we show that a similar inequality does not exist among twist-three quark distributions. We demonstrate that the inequality does not constrain the nucleon's tensor charge. Finally we explore physical mechanisms for saturating the inequality, arguing it is unlikely to occur in Nature.

hep-ph↗
arXiv1994

The Nucleon's Tensor Charge

We seek to understand the physical significance of the nucleon's tensor charge and make estimates of its size in phenomenological models and the QCD sum rule.

hep-ph↗
arXiv1994

Infrared Renormalons and Power Corrections in Deep-Inelastic Sum Rules

Infrared renormalons and $1/Q^2$ power corrections in deep-inelastic sum rules are studied. The renormalization of operators with power divergence are discussed. The higher-twist terms in the operator product expansion are shown to account for the residual soft contributions survived from the Kinoshita-Lee-Nauenberg type of cancellation in Feynman diagrams. The presence of some degree of arbitrariness in the twist separation allows one to define the most convenient higher-twist operators suitable for a particular non-perturbative method. The discussion is focused on the Bjorken sum rule, for which the $1/Q^2$ corrections are considered on a lattice.

hep-ph↗
arXiv1994

Probing Quark Fragmentation Functions for Spin-1/2 Baryon Production in Unpolarized $e^+e^-$ Annihilation

We study the measurement of the quark fragmentation functions for spin-1/2 baryon production ($Λ$ and $\bar Λ$, in particular) in unpolarized $e^+e^-$ annihilation. The spin-dependent fragmentation functions $\hat g_1(z)$ and $\hat h_1(z)$ can be probed in the process as a result of quark-antiquark spin correlation and the weak decay of the baryons. The relevant cross section is expressed as a product of the two-jet cross-section, the fragmentation functions, and the differential width of the hyperon decay.

hep-ph↗
arXiv1994

A QCD Analysis of the Mass Structure of the Nucleon

{}From the deep-inelastic momentum sum rule and the trace anomaly of the energy-momentum tensor, I derive a separation of the nucleon mass into the contributions of the quark and gluon kinetic and potential energies, the quark masses, and the trace anomaly.

hep-ph↗
arXiv1994

Parton-Hadron Duality: Resonances and Higher Twists

We explore the physics of the parton-hadron duality in the nucleon structure functions appearing in lepton-nucleon scattering. We stress that the duality allows one to extract the higher-twist matrix elements from data in the resonance region, and learn about the properties of resonances if these matrix elements are known. As an example, we construct the moments of $F_2(x, Q^2)$ for the low and medium $Q^2$ region, and from which we study the interplay between higher twists and the resonance contributions.

hep-ph↗
arXiv1994

$Q^2$-Dependence of Deep Inelastic Sum Rules

In this talk, I will concentrate on $Q^2$-dependence of deep inelastic sum rules. I will first give a modern definition of deep-inelastic sum rules and then discuss physical origins of their scaling violation at finite $Q^2$. Following this, I discuss a few well-known examples, in particular, the Bjorken sum rule, which is at the center of interest of this symposium. Finally, I consider the $Q^2 \to 0$ limit of sum rules using low-energy theorems. I think this can motivate some interesting CEBAF physics.

hep-ph↗
arXiv1994

Quark Fragmentation Functions in Low-Energy Chiral Theory

We examine the physics content of fragmentation functions for inclusive hadron production in a quark jet and argue that it can be calculated in low energy effective theories. As an example, we present a calculation of $u$-quark fragmentation to $π^+$ and $π^-$ mesons in the lowest order in the chiral quark model. The comparison between our result and experimental data is encouraging.

hep-ph↗
arXiv1993

Q^2-Dependence of the Proton's G_1 Structure Function Sum Rule

We study the $Q^2$ variation of the first moment of the nucleon's spin-dependent structure function $G_1$. As $Q^2 \rightarrow 0$ the moment is determined by the low energy theorem for Compton scattering. In the deep-inelastic region the moment is calculated using twist expansion to order $1/Q^2$. Based on these limits, we construct a formula which smoothly interpolates between the two regions.

hep-ph↗
arXiv1993

Chiral-Symmetry and Strange Four-Quark Matrix Elements

We consider the matrix elements of the left-handed flavor-conserving four-quark operators in the nucleon and pion states. Using chiral symmetry, we derive relationships among these matrix elements. We argue that the $ΔI = 1/2$ rule of hyperon and kaon non-leptonic weak decay implies possible large strange-quark content in the nucleon and pion.

hep-ph↗