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Dive into the research topics where Xiang-Song Chen is active.

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Featured researches published by Xiang-Song Chen.


Physical Review Letters | 2008

Spin and orbital angular momentum in gauge theories: nucleon spin structure and multipole radiation revisited.

Xiang-Song Chen; Xiao-Fu Lü; Wei-Min Sun; Fan Wang; T. Goldman

We address and solve the long-standing gauge-invariance problem of the nucleon spin structure. Explicitly gauge-invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task and opens a more promising avenue towards the understanding of the nucleon spin. Our research also justifies the traditional use of the canonical, gauge-dependent angular momentum operators of photons and electrons in the multipole-radiation analysis and labeling of atomic states and sheds much light on the related energy-momentum problem in gauge theories, especially in connection with the nucleon momentum.Parallel to the construction of gauge invariant spin and orbital angular momentum for QED in paper (I) of this series, we present here an analogous but non-trivial solution for QCD. Explicitly gauge invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task, and opens a more promising avenue towards the understanding of the nucleon spin structure.


Physical Review Letters | 2009

Do gluons carry half of the nucleon momentum

Xiang-Song Chen; Wei-Min Sun; Xiao-Fu Lü; Fan Wang; T. Goldman

We examine the conventional picture that gluons carry about half of the nucleon momentum in the asymptotic limit. We show that this large fraction is due to an unsuitable definition of the gluon momentum in an interacting theory. If defined in a gauge-invariant and consistent way, the asymptotic gluon momentum fraction is computed to be only about one-fifth. This result suggests that the asymptotic limit of the nucleon spin structure should also be reexamined. A possible experimental test of our finding is discussed in terms of novel parton distribution functions.


Physical Review D | 1998

Is nucleon spin structure inconsistent with the constituent quark model

Di Qing; Fan Wang; Xiang-Song Chen

A qualitative QCD analysis and a quantitative model calculation are given to show that the constituent quark model remains a good approximation even with the nucleon spin structure revealed in polarized deep inelastic scattering taking into account.


Physical Review A | 2010

Gauge-invariant hydrogen-atom Hamiltonian

Wei-Min Sun; Xiang-Song Chen; Xiao-Fu Lü; Fan Wang

For quantum mechanics of a charged particle in a classical external electromagnetic field, there is an apparent puzzle that the matrix element of the canonical momentum and Hamiltonian operators is gauge dependent. A resolution to this puzzle was recently provided by us [X.-S. Chen et al., Phys. Rev. Lett. 100, 232002 (2008)]. Based on the separation of the electromagnetic potential into pure-gauge and gauge-invariant parts, we have proposed a new set of momentum and Hamiltonian operators which satisfy both the requirement of gauge invariance and the relevant commutation relations. In this paper we report a check for the case of the hydrogen-atom problem: Starting from the Hamiltonian of the coupled electron, proton, and electromagnetic field, under the infinite proton mass approximation, we derive the gauge-invariant hydrogen-atom Hamiltonian and verify explicitly that this Hamiltonian is different from the Dirac Hamiltonian, which is the time translation generator of the system. The gauge-invariant Hamiltonian is the energy operator, whose eigenvalue is the energy of the hydrogen atom. It is generally time dependent. In this case, one can solve the energy eigenvalue equation at any specific instant of time. It is shown that the energy eigenvalues are gauge independent, and by suitably choosing themorexa0» phase factor of the time-dependent eigenfunction, one can ensure that the time-dependent eigenfunction satisfies the Dirac equation.«xa0less


Physics Letters B | 2003

A note on transverse axial vector and vector anomalies in U(1) gauge theories

Wei-Min Sun; Hong-Shi Zong; Xiang-Song Chen; Fan Wang

Abstract The transverse axial vector and vector anomalies in four-dimensional U (1) gauge theories studied in [Phys. Lett. B 507 (2001) 351] is reexamined by means of perturbative method. The absence of transverse anomalies for both axial vector and vector current is verified. We also show that the Pauli–Villars regularization and dimensional regularization gives the same result on the transverse anomaly of both axial vector and vector current.


Physical Review C | 2002

Nonperturbative aspects of axial vector vertex in the global color symmetry model

Hong-Shi Zong; Xiang-Song Chen; Fan Wang; Chaohsi Chang; En-Guang Zhao

The relation between the axial vector current of current quark and that of constituent quark has been studied within the framework of the global color symmetry model. Gluon dressing of the axial vector vertex and the quark self-energy function are described by the inhomogeneous Bethe-Salpeter equation in the ladder approximation and the Schwinger-Dyson equation in the rainbow approximation, respectively.


Chinese Physics Letters | 1999

Why the Constituent Quark Model Works for Baryon Magnetic Moments

Xiang-Song Chen; Di Qing; Fan Wang

Starting from quantum chromodynamics, we find that aside from some terms that contribute only via the mixing of different Fock components, the baryon magnetic moment can be expressed as μB = [∑qQq/(2κ0q)] (2Sq-2S+Lq-L), where κ0q is the q flavor quarks average relativistic energy inside the baryon, and Sq, Lq, S, L are quark and antiquarks relativistic spin and orbital contributions to baryon spin. We demonstrate that within an error of 1/6, this expression can be parameterized as ∑q[Qq/(2mqeff)] (2sq - 2s), (where s is the nonrelativistic Pauli spin contribution and mqeff is of the order of the constituent quark mass) which is just what the nonrelativistic constituent quark model adopts to give a good account of octet baryon magnetic moments.


Physical Review Letters | 2007

Spin and orbital angular momentum in gauge theories (II): QCD and nucleon spin structure

Xiang-Song Chen; Wei-Min Sun; Fan Wang; T. Goldman; Xiao-Fu Lü

We address and solve the long-standing gauge-invariance problem of the nucleon spin structure. Explicitly gauge-invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task and opens a more promising avenue towards the understanding of the nucleon spin. Our research also justifies the traditional use of the canonical, gauge-dependent angular momentum operators of photons and electrons in the multipole-radiation analysis and labeling of atomic states and sheds much light on the related energy-momentum problem in gauge theories, especially in connection with the nucleon momentum.Parallel to the construction of gauge invariant spin and orbital angular momentum for QED in paper (I) of this series, we present here an analogous but non-trivial solution for QCD. Explicitly gauge invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task, and opens a more promising avenue towards the understanding of the nucleon spin structure.


International Journal of Modern Physics A | 2004

THE TENSOR CURRENT DIVERGENCE EQUATION IN U(1) GAUGE THEORIES IS FREE OF ANOMALIES

Wei-Min Sun; Hong-Shi Zong; Xiang-Song Chen; Fan Wang

The possible anomaly of the tensor current divergence equation in U(1) gauge theories is calculated by means of perturbative method. It is found that the tensor current divergence equation is free of anomalies.


Physical Review Letters | 2008

Reply to the Comment on "Spin and orbital angular momentum in gauge theories: Nucleon spin structure and multipole radiation revisited" [PRL 100:232002 (2008)]

Xiang-Song Chen; Xiao-Fu Lü; Wei-Min Sun; Fan Wang; T. Goldman

We address and solve the long-standing gauge-invariance problem of the nucleon spin structure. Explicitly gauge-invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task and opens a more promising avenue towards the understanding of the nucleon spin. Our research also justifies the traditional use of the canonical, gauge-dependent angular momentum operators of photons and electrons in the multipole-radiation analysis and labeling of atomic states and sheds much light on the related energy-momentum problem in gauge theories, especially in connection with the nucleon momentum.Parallel to the construction of gauge invariant spin and orbital angular momentum for QED in paper (I) of this series, we present here an analogous but non-trivial solution for QCD. Explicitly gauge invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task, and opens a more promising avenue towards the understanding of the nucleon spin structure.

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T. Goldman

Los Alamos National Laboratory

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Th. Gutsche

University of Tübingen

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En-Guang Zhao

Chinese Academy of Sciences

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