arXiv subjects
Publications and source records attributed to Chung Wen Kao.
In this paper, we solve the gap equation of the Yang-Mills-Gribov-Zwanziger-Chern-Simon theory by considering the first order in the Chern-Simon topological mass term, $M$. As a result, we find three possible solutions to the gap equation, i.e. three different Gribov parameters. In addition, we analyze the regime of the theory for each of these Gribov parameters and we obtain a different result from the literature.
We estimate the unpolarized dihadron fragmentation functions (uDiFFs) within the framework of the single-cascade jet algorithm. We first obtain the elementary fragmentation functions generating the single hadron fragmentation functions by using the single-cascade jet algorithm. These results are very close to the empirical parametrizations of the single hadron fragmentation functions which are extracted from the experimental data of the $e^+e^-$ annihiliation and semi-inclusive deeply inelastic scatterings (SIDIS). We then use those elementary fragmentation functions to generate the dihadron fragmentation functions by the help of the single-cascade jet algorithm again. The comparison between our empirical results with the results of the Nambu-Jona-Lasinio model and the non-local chiral quark model (NL$χ$QM) is also presented.
There is an apparent discrepancy between the results of the charged kaon multiplicities off the deuteron target from HERMES and COMPASS experiments. In this article we point out that this discrepancy cannot be explained by different $Q^2$ values. Furthermore we examine the empirical parametrization of the fragmentation functions, DSS2017 carefully and find that the agreement between the theoretical estimate and the HERMES data is less satisfactory as claimed.
We present our analysis on the valence quark distribution functions of the $K^{+}$ meson, $v^{K (u)} (x, Q^2)$ and $v^{K (\bar{s})} (x, Q^2)$, taking into account the meson cloud effects in the framework of the chiral constituent quark model. Assuming appropriate bare quark distribution functions at the initial scale, evaluating the Goldstone boson dressing corrections with the model, and performing the QCD evolution, one can obtain the realistic dressed distributions at a certain scale. The phenomenologically satisfactory valence quark distribution of the pion was obtained in the previous study and there are available experimental data of the valence $u$ quark distribution ratio $v^{K(u)} (x, Q^2) / v^{π(u)} (x, Q^2)$, which enable us to obtain the kaon quark distribution functions. Besides presenting the resulting dressed distributions, we also show how the meson cloud effects affect the bare distributions in detail. A striking result is that the observed size of the SU(3) flavor symmetry breaking is considerably smaller than those seen in the preceding works based on other approaches.
We investigate the valence $u$ and $\bar{s}$ quark distribution functions of the $K^+$ meson, $v^{K(u)}(x,Q^2)$ and $v^{K(\bar{s})}(x,Q^2)$, in the framework of the chiral constituent quark model. We judiciously choose the bare distributions at the initial scale to generate the dressed distributions at the higher scale, considering the meson cloud effects and the QCD evolution, which agree with the phenomenologically satisfactory valence quark distribution of the pion and the experimental data of the ratio $v^{K(u)}(x,Q^2)/v^{π(u)}(x,Q^2)$. We show how the meson cloud effects affect the bare distribution functions in detail. We find that a smaller $SU(3)$ flavor symmetry breaking effect is observed, compared with results of the preceding studies based on other approaches.
We present a detailed derivation of the two sum rules relating the spin polarizabilities measured in real, virtual, and doubly-virtual Compton scattering. For example, the polarizability $δ_{LT}$, accessed in inclusive electron scattering, is related to the spin polarizability $γ_{E1E1}$ and the slope of generalized polarizabilities $P^{(M1,M1)1}-P^{(L1,L1)1}$, measured in, respectively, the real and the virtual Compton scattering. We verify these sum rules in different variants of chiral perturbation theory, discuss their empirical verification for the proton, and prospect their use in studies of the nucleon spin structure.
We investigate the valence quark distribution function of the pion $v^π(x,Q^2)$ in the framework of the chiral constituent quark model and evaluate the meson cloud effects on $v^π(x,Q^2)$. We explicitly demonstrate how the meson cloud effects affect $v^π(x,Q^2)$ in detail. We find that the meson cloud correction causes an overall 32\% reduction of the valence quark distribution and an enhancement at the small Bjorken $x$ regime. Besides, we also find that the dressing effect of the meson cloud will make the valence quark distribution to be softer in the large $x$ region.
We investigate the unpolarized pion and kaon fragmentation functions using the nonlocal chiral-quark model. In this model the interactions between the quarks and pseudoscalar mesons is manifested nonlocally. In addition, the explicit flavor SU(3) symmetry breaking effect is taken into account in terms of the current quark masses. The results of our model are evaluated to higher $Q^2$ value $Q^2=4\,\mathrm{GeV}^2$ by the DGLAP evolution. Then we compare them with the empirical parametrizations. We find that our results are in relatively good agreement with the empirical parametrizations and the other theoretical estimations.
We investigate the chiral restoration at finite temperature $(T)$ under the strong external magnetic field $\vec{B}=B_{0}\hat{z}$ of the SU(2) light-flavor QCD matter. We employ the instanton-liquid QCD vacuum configuration accompanied with the linear Schwinger method for inducing the magnetic field. The Harrington-Shepard caloron solution is used to modify the instanton parameters, i.e. the average instanton size $(\barρ)$ and inter-instanton distance $(\bar{R})$, as functions of $T$. In addition, we include the meson-loop corrections (MLC) as the large-$N_{c}$ corrections because they are critical for reproducing the universal chiral restoration pattern. We present the numerical results for the constituent-quark mass as well as chiral condensate which signal the spontaneous breakdown of chiral-symmetry (SB$χ$S), as functions of $T$ and $B$. Besides we find that the changes for the $F_π$ and $m_π$ due to the magnetic field is relatively small, in comparison to those caused by the finite $T$ effect.
To resolve the puzzle of the proton size raised from the recent result of muonic hydrogen Lamb shift, De Rújula has proposed that a large value of the third Zemach moment $< r^3_{p}>{(2)}$ of the proton to be the solution. His suggestion has been criticized by many groups based on the $ep$ scattering data at low $Q^2$ regime. However, if there is a "thorn" or "lump" in the electric form factor of the proton $G_{E}(Q^2)$ at extremely low $Q^2$ regime, then the third Zemach moment $< r^3_{p}>{(2)}$ would be as large as De Rújula suggested. In this article, we show that the existence of such a "thorn" or "lump" has not been completely excluded, although tightly restricted, by the current data of $ep$ elastic scattering. We also suggest a more sophisticated global fitting procedure of $G_{E}(Q^2)$ for the future fitting.
The details of the calculation of the two-boson exchange effects in the parity-violating elastic $ep$ scattering within a simple hadronic model, including both the nucleon and $Δ(1232)$-resonance intermediate states, are presented. We examine the sensitivity of our results with respect to choice of form factors. We emphasize the importance to use correct relations relating N to $Δ$ and $Δ$ to N transition vertex functions. The $NΔ$ Coulomb quadrupole transition is found to play important role at higher $Q^2\geq 3.0$ GeV$^2$. We also elucidate the relation between our results and the well-known result on the $γZE$ effect given by Marciano and Sirlin (MS). The effect of the nucleon contribution $δ_N$ to parity-asymmetry $A_{PV}$, is found to be in general, larger than the corresponding $Δ$ contribution $δ_Δ$ except at extreme forward angles. The corrections to the extracted values of the strange form factors $G^{s}_{E}+βG^{s}_{M}$ from the HAPPEX, A4, and G0 data are also presented. The total TBE corrections to the extracted values of $G^{s}_{E}+βG^{s}_{M}$ in recent experiments of HAPPEX G0, and A4 are, depending on kinematics, found to be small except in a few cases where they range from -20.6% to $48.3 %$.
We study the leading electroweak corrections in the precision measurement of the strange form factors. Specifically, we calculate the two-boson-exchange (TBE), two-photon-exchange (TPE) plus $γZ$-exchange ($γZ$E), corrections with $Δ(1232)$ excitation to the parity-violating asymmetry of the elastic electron-proton scattering. The interplay between nucleon and $Δ$ contributions is found to depend strongly on the kinematics, as $δ_Δ$ begins as negligible at backward angles but becomes very large and negative and dominant at forward angles, while $δ_N$ always stays positive and decreases monotonically with increasing $ε$. The total TBE corrections to the extracted values of $G^{s}_{E}+βG^{s}_{M}$ in recent experiments of HAPPEX and G0 are, depending on kinematics, found to be large and range between 13% to -75% but small in the case of A4 experiments.
We calculate $γZ$ exchange corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a parton model using the formalism of generalized parton distributions(GPDs). We also examine the validity of the zero-momentum-transfer approximation adopted in the literatures and find that it overestimates the $γZ$ exchange effect significantly at the forward scattering angles.
We calculate the two-boson-exchange (TBE) corrections to the parity asymmetry of the elastic electron-proton scattering in a model using the formalism of generalized parton distributions (GPDs).
We calculate the two-boson-exchange (TBE) corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a simple hadronic model including the nucleon and the $Δ(1232)$ intermediate states. We find that $Δ$ contribution $δ_Δ$ is, in general, comparable with the nucleon contribution $δ_N$ and the current experimental measurements of strange-quark effects in the proton neutral weak current. The total TBE corrections to the current extracted values of $G^{s}_{E}+βG^{s}_{M}$ in recent experiments are found to lie in the range of $-7\sim +7%$.
Leading electroweak corrections play an important role in precision measurements of the strange form factors. We calculate the two-photon-exchange (TPE) and $γZ$-exchange corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a simple hadronic model including the finite size of the proton. We find both can reach a few percent and are comparable in size with the current experimental measurements of strange-quark effects in the proton neutral weak current. The effect of $γZ$-exchange is in general larger than that of TPE, especially at low momentum transfer $Q^2\le 1 GeV^2$. Their combined effects on the values of $G^s_E+βG^s_M$ extracted in recent experiments can be as large as -40% in certain kinematics.
The general form of the cross section as well as the polarizations of electron-deuteron elastic scattering are given. Two-photon exchange effects are analyzed. Possible signatures of the two-photon exchange effects in the electron-deuteron elastic scattering are discussed.
We present the first heavy baryon chiral perturbation theory calculation at ${\mathcal O}(p^4)$ for the spin-dependent amplitudes for virtual Compton scattering off the nucleon, and extract the ${\cal O}(p^4)$ order results for the generalized spin polarizabilities of the nucleon.