arXiv subjects
Publications and source records attributed to Xiao-Jun Wang.
In terms of effective field theory and mixed propagator approach, we show that there is a larger hidden effect of isospin breaking in $ρ^0\toπ^0γ$ decay due to an $ω$ exchange, $ρ^0\toω\toπ^0γ$. The branching ratio is predicted as $B(ρ^0\toπ^0γ)=(11.67\pm 2.0)\times 10^{-4}$, which is much larger than Partcile Data Group's datum $(6.8\pm 1.7)\times 10^{-4}$ and one of charged mode, $B(ρ^\pm\toπ^\pmγ)=(4.5\pm 0.5)\times 10^{-4}$.
We propose a new algebraic deformation of ${\cal N}=4$ SYM via decomposition of spinor and scalar fields in vector supermultiplet. This decomposition generates degrees of freedom of usual quarks and leptons and the deformation model is a low energy effective model. We show that supersymmetry is broken in certain limit and the deformation model reduces to a SM-like model, or a QCD-like model. Meanwhile, gauge symmetry can be spontaneously broken by nontrivial supersymmetry vacuum.
Mixed Propagator (MP) approach to $ρ-ω$ mixing is discussed. It is found that under the pole-approximation assumption the results of MP approach is not compatible both with the effective Lagrangian theory and with the experiment measurement criterion. To overcome these inconsistent, we propose a new MP approach in which the physical states of $ρ$ and $ω$ are determined by the requirement of experimental measurement to meson resonance. In terms of this new MP approach, the EM pion form factor $F_π$ and form factors of $ρ^0 \to π^0 γ$ and of $ω\to π^0 γ$ are derived. The results of $F_π$ are in good agreement with data. The form factor of $ρ^0 \to π^0 γ$ exhibits a hidden charge-asymmetry enhancement effect which agree with the prediction of the effective Lagrangian theory.
The muon anomalous $g$ value, $a_μ=(g-2)/2$, is calculated up to one-loop level in noncommutative QED. We argue that relativistic muon in E821 experiment nearly always stays at the lowest Landau level. So that spatial coordinates of muon do not commute each other. Using parameters of E821 experiment, $B=14.5$KG and muon energy 3.09GeV/c, we obtain the noncommutativity correction to $a_μ$ is about $1.57\times 10^{-9}$, which significantly makes standard model prediction close to experiment.
We study physics on $ρ(770)$ and $ω(782)$ in framework of chiral constituent quark model. The effective action is derived by proper vertex method, which can capture all order information of chiral expansion. The $N_c^{-1}$ expansion is also studied systematically. It is shown that the momentum expansion at vector meson energy scale converges slowly, and the loop effects of pseudoscalar meson play an important role at this energy scale. We provide a method to prove the unitarity of S-matrix in any low-energy effective theory of QCD. Phenomenologically, we study decays for $ρ\toππ$, $ρ\to e^+e^-$, $ω\toπ^+π^-$, $ρ^\pm\toγπ^\pm$ and $ω\toγπ^0$, $ρ^0-ω$ mixing and their mass splitting, pion form factor, $I=l=1$ phase shift and light quark masses at vector meson energy scale. These results include all order contribution of vector meson momentum expansion and is up to next to leading order of $N_c^{-1}$ expansion. All of these theoretical predictions agree with data very well. The unitarity of S-matrix yielded by this framework is examined. The Breit-Winger formula for resonance propagator is derived.
We study chiral expansion at $m_ρ$-scale in framework of chiral constituent quark model. The lowest vector meson resonsances are treated as composited fields of constituent quarks. We illustrate that, at energy scale of $ρ$-meson mass, the chiral expansion expansion converges slowly. Therefore, it is possible to construct a well-defined chiral effective field theory at this energy scale, but high order correction of chiral expansion must be included simultanously. The one-loop correction of pseudoscalar mesons is also studied systematically. The unitarity of the model is examined and Breit-Wigner formula for $ρ$-meson is obtained. The prediction on on-shell $ρ\toππ$ and $ρ\to e^+e^-$ decays agree with data very well.
We study $e^+e^-\toπ^+π^-$ cross section and phase shift of $I=l=1$ $π-π$ scattering below 1GeV in framework of chiral constituent quark model. The results including all order contribution of the chiral perturbation expansion and all one-loop effects of pseudoscalar mesons, but without any adjust parameters. Width of $ρ$ predicted by the model strongly depends on transition momentum-square $q^2$. We show that the mass pamameter of $ρ$-meson in its propagator is very different from its physical mass due to momentum-dependent width of $ρ$. The mass difference between $ρ^0$ and $ω$ are predicted successfully. The rigorous theoretical prediction on $e^+e^-\toπ^+π^-$ cross section and the phase shift in $I=l=1$ $π-π$ scattering agree with data excellentlly.
We study SU(3)$_L\timesSU(3)_R$ chiral quark model of mesons up to the next to leading order of $1/N_c$ expansion. Composite vector and axial-vector mesons resonances are introduced via non-linear realization of chiral SU(3) and vector meson dominant. Effects of one-loop graphs of pseudoscalar, vector and axial-vector mesons is calculated systematically and the significant results are obtained. We also investigate correction of quark-gluon coupling and relationship between chiral quark model and QCD sum rules. Up to powers four of derivatives, chiral effective lagrangian of mesons is derived and evaluated to the next to leading order of $1/N_c$. Low energy limit of the model is examined. Ten low energy coupling constants $L_i(i=1,2,...,10)$ in ChPT are obtained and agree with ChPT well.
We examine low energy limit of $U(3)_L\times U(3)_R$ chiral theory of mesons through integrating out fields of vector and axial-vector mesons. The effective lagrangian for pseudoscalar mesons at $O(p^4)$ has been obtained, and five low energy coupling constants $L_i(i=1,2,3,9,10)$ have been revealed. They are in good agreement with the results of CHPT's at $μ\sim m_ρ$.