arXiv subjects

Z. G. Wang

Publications and source records attributed to Z. G. Wang.

32 records · Page 2Linked to original sources

arXiv2007

Structure and decay constant of the ρmeson with Bethe-Salpeter equation

In this article, we study the structure of the ρmeson in the framework of the coupled rainbow Schwinger-Dyson equation and ladder Bethe-Salpeter equation with a confining effective potential. The u and d quark propagators get significantly modified, the mass poles are absent in the timelike region, which implements confinement naturally. The Bethe-Salpeter amplitudes of the ρmeson center around zero momentum and extend to the energy scale about $q^2=1GeV^2$, which happens to be the energy scale of chiral symmetry breaking, strong interactions in the infrared region result in bound state. The numerical results of the mass and decay constant of the ρmeson are in agreement with the experimental data.

hep-ph↗

arXiv2007

Bosonization study of quantum phase transitions in the one-dimensional asymmetric Hubbard model

The quantum phase transitions in the one-dimensional asymmetric Hubbard model are investigated with the bosonization approach. The conditions for the phase transition from density wave to phase separation, the correlation functions and their exponents are obtained analytically. Our results show that the difference between the hopping integrals for up- and down-spin electrons is crucial for the happening of the phase separation. When the difference is large enough, the phase separation will appear even if the on-site interaction is small.

cond-mat.str-el↗

arXiv2007

Analysis of the vector form factors $f^+_{Kπ}(Q^2)$ and $f^-_{Kπ}(Q^2)$ with light-cone QCD sum rules

In this article, we calculate the vector form factors $f^+_{Kπ}(Q^2)$ and $f^-_{Kπ}(Q^2)$ within the framework of the light-cone QCD sum rules approach. The numerical values of the $f^+_{Kπ}(Q^2)$ are compatible with the existing theoretical calculations, the central value of the $f^+_{Kπ}(0)$, $f^+_{Kπ}(0)=0.97$, is in excellent agreement with the values from the chiral perturbation theory and lattice QCD. The values of the $|f^-_{Kπ}(0)|$ are very large comparing with the theoretical calculations and experimental data, and can not give any reliable predictions. At large momentum transfers with $Q^2> 5GeV^2$, the form factors $f^+_{Kπ}(Q^2)$ and $|f^-_{Kπ}(Q^2)|$ can either take up the asymptotic behavior of $\frac{1}{Q^2}$ or decrease more quickly than $\frac{1}{Q^2}$, more experimental data are needed to select the ideal sum rules.

hep-ph↗

arXiv2007

Structure of the axial-vector meson $D_{s1}(2460)$ and the strong coupling constant $g_{D_{s1} D^* K}$ with the light-cone QCD sum rules

In this article, we take the point of view that the charmed axial-vector meson $D_{s1}(2460)$ is the conventional $c\bar{s}$ meson and calculate the strong coupling constant $g_{D_{s1} D^* K}$ in the framework of the light-cone QCD sum rules approach. The numerical values of strong coupling constants $g_{D_{s1} D^* K}$ and $g_{D_{s0} D K}$ are very large, and support the hadronic dressing mechanism. Just like the scalar mesons $f_0(980)$ and $a_0(980)$, the scalar meson $D_{s0}(2317)$ and axial-vector meson $D_{s1}(2460)$ may have small $c\bar{s}$ kernels of the typical $c\bar{s}$ meson size, the strong couplings to the hadronic channels (or the virtual mesons loops) may result in smaller masses than the conventional $c\bar{s}$ mesons in the constituent quark models, and enrich the pure $c\bar{s}$ states with other components.

hep-ph↗

arXiv2007

Analysis of the $Σ-n $ form factors with light-cone QCD sum rules

In this work, we study the four form-factors $f_1(Q^2)$, $f_2(Q^2)$, $g_1(Q^2)$ and $g_2(Q^2)$ of the $Σ\to n$ in the framework of the light-cone QCD sum rules approach up to twist-6 three valence quark light-cone distribution amplitudes. The $f_1(0)$ is the basic input parameter in extracting the CKM matrix element $|V_{us}|$ from the hyperon decays. The four form-factors $f_1(Q^2)$, $f_2(Q^2)$, $g_1(Q^2)$ and $g_2(Q^2)$ at intermediate and large momentum transfers with $Q^2> 3 GeV^2$ have significant contributions from the end-point (soft) terms. The numerical values of the four form-factors $f_1(0)$, $f_2(0)$, $g_1(0)$ and $g_2(0)$ are compatible with the experimental data and theoretical calculations (in magnitude); although the uncertainties are large.

hep-ph↗

arXiv2006

Analysis of the vertices $D^D_sK$, $D^_sDK$,$D_0D_sK$ and $D_{s0}DK$ with the light-cone QCD sum rules

In this article, we analyze the vertices $D^*D_sK$, $D^*_sDK$, $D_0D_sK$ and $D_{s0}DK$ within the framework of the light-cone QCD sum rules approach in an unified way. The strong coupling constants $G_{D^*D_sK}$ and $G_{D^*_sDK}$ are important parameters in evaluating the charmonium absorption cross sections in searching for the quark-gluon plasmas, our numerical values of the $G_{D^*D_sK}$ and $G_{D^*_sDK}$ are compatible with the existing estimations although somewhat smaller, the SU(4) symmetry breaking effects are very large, about 60%. For the charmed scalar mesons $D_0$ and $D_{s0}$, we take the point of view that they are the conventional $c\bar{u}$ and $c\bar{s}$ mesons respectively, and calculate the strong coupling constants $G_{D_0 D_s K}$ and $G_{D_{s0} D K}$ with the vector interpolating currents. The numerical values of the scalar-$D_sK$ and -$DK$ coupling constants $G_{D_0 D_s K}$ and $G_{D_{s0} D K}$ are compatible with the existing estimations, the large values support the hadronic dressing mechanism. Furthermore, we study the dependence of the four strong coupling constants $G_{D^*D_sK}$, $G_{D^*_sDK}$, $G_{D_0D_sK}$ and $G_{D_{s0}DK}$ on the non-perturbative parameter $a_4$ of the twist-2 $K$ meson light-cone distribution amplitude.

hep-ph↗

arXiv2006

Ground state mass spectrum for scalar diquarks with Bethe-Salpeter equation

In this article, we study the structures of the pseudoscalar mesons $π$, $K$ and the scalar diquarks $U^a$, $D^a$, $S^a$ in the framework of the coupled rainbow Schwinger-Dyson equation and ladder Bethe-Salpeter equation with the confining effective potential. The $u$, $d$, $s$ quarks have small current masses, and the renormalization is very large, the mass poles in the timelike region are absent which implements confinement naturally. The Bethe-Salpeter wavefunctions of the pseudoscalar mesons $π$, $K$ and the scalar diquarks $U^a$, $D^a$, $S^a$ have the same type (Gaussian type) momentum dependence, center around zero momentum and extend to the energy scale about $q^2=1GeV^2$ which happen to be the energy scale for the chiral symmetry breaking, the strong interactions in the infrared region result in bound (or quasi-bound) states. The numerical results for the masses and decay constants of the $π$, $K$ mesons can reproduce the experimental values, the ground state masses of the scalar diquarks $U^a$, $D^a$, $S^a$ are consistent with the existing theoretical calculations. We suggest a new Lagrangian which may explain the uncertainty of the masses of the scalar diquarks .

hep-ph↗

arXiv2006

Structure of the $D_{s0}(2317)$ and the strong coupling constant $g_{D_{s0} D K}$ with the light-cone QCD sum rules

In this article, we take the point of view that the charmed scalar meson $D_{s0}(2317)$ is the conventional $c\bar{s}$ meson and calculate the strong coupling constant $g_{D_{s0} D K}$ within the framework of the light-cone QCD sum rules approach. The numerical values for the large scalar-$DK$ coupling constant $g_{D_{s0} D K}$ support the hadronic dressing mechanism. Just like the scalar mesons $f_0(980)$ and $a_0(980)$, the $D_{s0}(2317)$ may have small scalar $c\bar{s}$ kernel of the typical $c\bar{s}$ meson size. The strong coupling to the hadronic channels (or the virtual mesons loops) may result in smaller mass than the conventional scalar $c\bar{s}$ meson in the constituent quark models, and enrich the pure $c\bar{s}$ state with other components. The $D_{s0}(2317)$ may spend part (or most part) of its lifetime as virtual $ D K $ state.

hep-ph↗

arXiv2005

A new approach for calculating the Nambu-Gorkov propagator in color superconductivity theory

In this article, we propose a new approach to calculate the Nambu-Gorkov propagator intuitively with some linear algebra techniques in presence of the scalar diquark condensates. With the help of energy projective operators, we can obtain relatively simple expressions for the quark propagators, which greatly facilitate the calculations in solving the Schwinger-Dyson equation to obtain the gap parameters.

hep-ph↗

arXiv2004

Decay constants of the pseudoscalar mesons in the framework of the coupled Schwinger-Dyson equation and Bethe-Salpeter equation

In this article, we investigate the structures of the pseudoscalar mesons ($π$, $K$, $D$, $D_s$, $B$ and $B_s$) in the framework of the coupled rainbow Schwinger-Dyson equation and ladder Bethe-Salpeter equation with the confining effective potential (infrared modified flat bottom potential). The Schwinger-Dyson functions for the $u$, $d$ and $s$ quarks are greatly renormalized at small momentum region and the curves are steep at about $q^2=1GeV^2$ which indicates an explicitly dynamical symmetry breaking. The Euclidean time fourier transformed quark propagators have no mass poles in the time-like region which naturally implements confinement. As for the $c$ and $b$ quarks, the current masses are very large, the renormalization are more tender, however, mass poles in the time-like region are also absent. The Bethe-Salpeter wavefunctions for those mesons have the same type (Gaussian type) momentum dependence and center around small momentum which indicate that the bound states exist in the infrared region. The decay constants for those pseudoscalar mesons are compatible with the values of experimental extractions and theoretical calculations, such as lattice simulations and QCD sum rules.

hep-ph↗

arXiv2003

Calculation of the Chiral Lagrangian Coefficients

We present a systematic way to combine the global color model and the instanton liquid model to calculate the chiral Lagrangian coefficients. Our numerical results are in agreement well with the experimental values.

hep-ph↗

arXiv2003

Calculation of some properties of the vacuum

In this article, we calculate the dressed quark propagator with the flat bottom potential in the framework of the rain-bow Schwinger-Dyson equation, which is determined by mean field approximation of the global colour model lagrangian. The dressed quark propagator exhibits a dynamical symmetry breaking phenomenon and gives a constituent quark mass about 392 MeV, which is close to the value of commonly used constituent quark mass in the chiral quark model. Then based on the dressed quark propagator, we calculate some properties of the vacuum, such as quark condensate, mixed quark condensate $g_{s}< 0|\bar{q}G_{μν}σ^{μν}q|0>$, four quark condensate $<0|\bar{q} Γq\bar{q} Γq |0>$, tensor, $π$ vacuum susceptibilities. The numerical results are compatible with the values of other theoretical approaches.

hep-ph↗

arXiv2002

Calculation of the quark condensate through Schwinger-Dyson equation

In this letter, we clarify the algebra expression for calculating the quark condensate based on the non-perturbative quark propagator calculated through Schwinger-Dyson equation. The quark condensates, which characterize the low energy QCD vacuum, should not get a divergent quantity at large energy scale; the re-normalization group evolution behaviour at large energy scale therefore should be interpreted as "smeared collective effects" for it contains both perturbative and non-perturbative parts. We prefer the integral expression and get a quantity which is both convergent and scale dependent.

hep-ph↗

arXiv2002

Dynamical symmetry breaking, confinement with flat-bottom potential

In this article, we calculate the dressed quark propagator with the flat bottom potential in the framework of the rain-bow Schwinger-Dyson equation. Then based on the nonperturbative dressed quark propagator, we calculate the $π$ decay constant and the quark condensate. The $π$ decay constant is an important parameter in describing the interplay between dynamical symmetry breaking and confinement, while the quark condensate is an order parameter for dynamical chiral symmetry breaking. To implement confinement, we prove that the dressed quark propagator has no poles on the real timelike $p^2$ axial, the absence of Kallen-Lehmann spectral representation obviously precludes the existence of free quarks.

hep-ph↗