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Hong-Shi Zong

Publications and source records attributed to Hong-Shi Zong.

At least 55 records · Page 3Linked to original sources
arXiv2018

Finite volume effects on the chiral phase transition from Dyson-Schwinger equations of QCD

Within the framework of Dyson-Schwinger equations of QCD, we study the finite volume effects on the chiral phase transition, especially the influence on the position of the possible pseudo-critical end point (pCEP). The results show that in the chiral limit case (the current quark mass $m=0$), the absolute value of quark condensate decreases for smaller volumes, and more interestingly, so does the pseudo-critical temperature $T_c(μ=0)$, which is in agreement with the Polyakov Nambu--Jona-Lasinio model result and opposite to the Polyakov linear sigma model prediction. These conclusions hold for $m>0$ case in our calculations. Moreover, the results of pCEP as a function of different volumes show that $T$ of pCEP also decreases for smaller volumes, but $μ$ of pCEP will increase, which are qualitatively more close to Polyakov linear sigma model results. For our model setup, results for systems with a size larger than (5 fm)$^3$ closely approximate those from infinite volume, but if the volume is smaller, the corrections are non-negligible, even significantly affect signatures of the results from an infinite system. There also exists some possibility that, if the system size is too small, the whole phase transition would be crossover, which means no pCEP exists at all. It is no doubt that, finite volume effects deserve further researches.

hep-ph↗
arXiv2018

Fermion Self-energy and Pseudovector Condensate in NJL Model with External Magnetic Field

In this paper, we aim to study the complete self-energy in the fermion propagator within two-flavor NJL model in the case of finite temperature, chemical potential and external magnetic field. Through Fierz transformation we prove that the self-energy is not simply proportional to dynamical mass in the presence of chemical potential, moreover, it contains four kinds of condensates after introducing external magnetic field. We find out the appropriate and complete form of self-energy and establish new gap equations. We take two of the four condensates (scalar and pseudovector condensates) to make an approximation and simplify the gap equations. The numerical results show that not only the dynamical mass get quantitative modification, but also the properties of Nambu phase and Wigner phase are significantly different with classic results. Instead of classic Wigner phase with zero dynamic mass in the massless NJL model, we propose a new phase - quasi-Wigner phase in this article, it has small but nonzero dynamic mass, with increasing chemical potential, eventually Nambu phase will turn into quasi-Wigner phase with first-order phase transition, therefore the chiral symmetry can never be fully restored but be partially restored. Furthermore, we prove that pseudovector condensate in self-energy can generate energy splitting in dispersion relation, it will cause minor differences of particle numbers with the split energy levels.

hep-th↗
arXiv2018

Constraints on the hybrid equation of state with a crossover hadron-quark phase transition in the light of GW170817

In this paper, we use the recent updated source properties of GW170817 to constrain the hybrid equation of state (EOS) constructed by a three-window modeling between the hadronic EOS and quark EOS. Specifically, the hadronic EOS is described by NL3$ωρ$ model whose corresponding pure neutron star (NS) is already excluded by the constraint of tidal deformability (TD) from GW170817, and the quark EOS is calculated with 2+1 flavors Nambu-Jona-Lasinio (NJL) model. We also consider other four constraints on the hybrid EOS. As a result, we find the parameter set ($B^{\frac{1}{4}}, \tildeμ, Γ$) can be well constrained, indicating the possible existence of the hybrid star (HS) with a crossover inside. The type of the two stars in the binary system for nine representative hybrid EOSs is shown in this paper too. Furthermore, the HSs restricted by five constraints do not suggest a pure quark core but a mixed-phase in center.

nucl-th↗
arXiv2018

Wigner solution of the quark gap equation

Solutions and their evolutions of the quark gap equation are studied within the Nambu-Jona--Lasinio model, which is a basic issue for studying the QCD phase structure and locating the possible critical end point. It is shown that in the chiral limit case of the vacuum, chiral symmetry will hold if the coupling strength $G$ is small, then the system only has the Wigner solution at $M=0$. If increasing $G$, two symmetric minima will appear as the positive and `negative' Nambu solutions, however, the solution $M=0$ now corresponds to a maximum instead of a minimum of the thermodynamical potential, so is not a physically stable state anymore (we call it `pseudo-Wigner solution'). Besides, it is shown that as the current quark mass $m$ increases, the pseudo-Wigner solution will become negative, and disappear together with the negative Nambu solution if $m$ is large enough. Similar things happen if we increase the temperature or quark chemical potential $μ$. Some interesting phenomenon is, from some $μ$ a second local minimum will show up. As $μ$ increases gradually, it will be stabler than the Nambu solution, survives even the Nambu solution disappears, and approaches $m$, which are just the features of the Wigner solution we expect.

hep-ph↗
arXiv2018

Revisiting heavy quark radiative energy loss in nuclei within the high-twist approach

We revisit the calculation of multiple parton scattering of a heavy quark in nuclei within the framework of recently improved high-twist factorization formalism, in which gauge invariance is ensured by a delicate setup of the initial partons' transverse momenta. We derive a new result for medium modified heavy quark fragmentation functions in deeply inelastic scattering. It is consistent with the previous calculation of light quark energy loss in the massless limit, but leads to a new correction term in the heavy quark case, which vanishes in the soft gluon radiation limit. We show numerically the significance of the new correction term in the calculation of heavy quark energy loss as compared to previous studies and with soft gluon radiation approximation.

hep-ph↗
arXiv2018

Pseudo-magnetic field and effective spin-orbit interaction for a spin-1/2 particle confined to a curved surface

By considering the spin connection, we deduce the effective equation for a spin-1/2 particle confined to a curved surface with the non-relativistic limit and in the thin-layer quantization formalism. We obtain a pseudo-magnetic field and an effective spin-orbit interaction generated by the spin connection. Geometrically, the pseudo-magnetic field is proportional to the Gaussian curvature and the effective spin-orbit interaction is determined by the Weingarten curvature tensor. Particularly, we find that the pseudo-magnetic field and the effective spin-orbit interaction can be employed to separate the electrons with different spin orientations. All these results are demonstrated in two examples, a straight cylindrical surface and a bent one.

quant-ph↗
arXiv2018

Probing Magnetic Fields of GRB X-ray Flares with Polarization Observations

X-ray flares, lasting for $\sim 100 - 1000$ s in the X-ray band, are often observed following gamma-ray bursts (GRBs). The physical origin of X-ray flares is still unknown merely with the temporal/spectral information. On the other hand, some polarimeters are expected to be launched within several years thanks to the increasing interest on astronomical X-ray polarimetry. Here, by assuming that X-ray flares are synchrotron radiation from relativistic spherical shells, we show that the linear polarization degree during the rising phase of an X-ray flare is much higher for the emitting region with toroidal magnetic fields than that with random magnetic fields. In the decay phase of the flare, the evolution of the polarization degree is determined by the curvature effect of the emitting shell, which is a natural feature of jet scenarios for flares. Therefore, the measurement of the polarization of X-ray flares would provide a useful tool to probe the configuration of magnetic fields in the emission region, and may even help to test the curvature effect. The information on the magnetic configuration can further help us to understand the properties of GRB jets.

astro-ph.HE↗
arXiv2018

Revisit of cosmic ray antiprotons from dark matter annihilation with updated constraints on the background model from AMS-02 and collider data

We study the cosmic ray antiprotons with updated constraints on the propagation, proton injection, and solar modulation parameters based on the newest AMS-02 data near the Earth and Voyager data in the local interstellar space, and on the cross section of antiproton production due to proton-proton collisions based on new collider data. We use a Bayesian approach to properly consider the uncertainties of the model predictions of both the background and the dark matter (DM) annihilation components of antiprotons. We find that including an extra component of antiprotons from the annihilation of DM particles into a pair of quarks can improve the fit to the AMS-02 antiproton data considerably. The favored mass of DM particles is about $60\sim100$ GeV, and the annihilation cross section is just at the level of the thermal production of DM ($\langleσv\rangle \sim O(10^{-26})$ cm$^3$~s$^{-1}$).

astro-ph.HE↗
arXiv2018

New Perspective on Hybrid Mesons

It is thought that strong interactions within the Standard Model can generate bound-states in which non-Abelian gauge-bosons play a dual role, serving both as force and matter fields. In this context we introduce a novel approach to the hybrid-meson (valence-gluon+quark+antiquark) bound-state problem in relativistic quantum field theory. Exploiting the existence of strong two-body correlations in the gluon-quark, $q_g=[gq]$, and gluon-antiquark, $\bar q_g=[g\bar q]$ channels, we argue that a sound description of hybrid properties can be obtained by solving a coupled-pair of effectively two-body equations; and, consequently, that hybrids may be viewed as highly-correlated $q_g \bar q \leftrightarrow q \bar q_g$ bound-states. Analogies may be drawn between this picture of hybrid structure and that of baryons, in which quark+quark (diquark) correlations play a key role. The potential of this formulation is illustrated by calculating the spectrum of light-quark isovector hybrid mesons.

nucl-th↗
arXiv2018

Studies of the structure of massive hybrid stars within a modified NJL model

In this paper, we use the equation of state based on a modification of 2+1 flavors Nambu-Jona- Lasinio (NJL) model to study the quark matter of hybrid stars. For comparison, we utilize five EOSs of the relativistic mean-field (RMF) model to describe the hadronic phase. With the 3- window crossover interpolation approach, we try to construct relatively soft hybrid EOSs but find the maximum masses of hybrid stars do not differ too much. The results are quite close to two solar mass, which is consistent with the mass constraint of PSR J0348+0432. Furthermore it is noteworthy that the heaviest stable stars have central densities higher than that of the deconfinement transition thus suggesting a pure quark core in the hybrid star.

nucl-th↗
arXiv2018

Robustness of the semimetal state of Na3Bi and Cd3As2 against Coulomb interaction

We study the excitonic semimetal-insulator quantum phase transition in three-dimensional Dirac semimetal in which the fermion dispersion is strongly anisotropic. After solving the Dyson-Schwinger equation for the excitonic gap, we obtain a global phase diagram in the plane spanned by the parameter for Coulomb interaction strength and the parameter for fermion velocity anisotropy. We find that excitonic gap generation is promoted as the interaction becomes stronger, but is suppressed if the anisotropy increases. Applying our results to two realistic three-dimensional Dirac semimetals Na$_{3}$Bi and Cd$_{3}$As$_{2}$, we establish that their exact zero-temperature ground state is gapless semimetal, rather than excitonic insulator. Moreover, these two materials are far from the excitonic quantum critical point, thus there should not be any observable evidence for excitonic insulating behavior. This conclusion is in general agreement with the existing experiments of Na$_{3}$Bi and Cd$_{3}$As$_{2}$.

cond-mat.str-el↗
arXiv2018

A new algorithm towards quasi-Wigner solution of the gap equation beyond the chiral limit

We propose a new algorithm to solve the quasi-Wigner solution of the gap equation beyond chiral limit. Employing a Gaussian gluon model and rainbow truncation, we find that the quasi-Wigner solution exists in a limited region of current quark mass, $m<43.1$ MeV, at zero temperature $T$ and zero chemical potential $μ$. The difference between Cornwall-Jackiw-Tomboulis (CJT) effective actions of quasi-Wigner and Nambu-Goldstone solutions shows that the Nambu-Goldstone solution is chosen by physics. Moreover, the quasi-Wigner solution is studied at finite temperature and chemical potential, the far infrared mass function of quasi-Wigner solution is negative and decrease along with $T$ at $μ=0$. Its susceptibility is divergent at certain temperature with small $m$, and this temperature decreases along with $m$. Taking $T=80$ MeV as an example, the quasi-Wigner solution is shown at finite chemical potential upto $μ=350$ MeV as well as Nambu solution, the coexistence of these two solutions indicates that the QCD system suffers the first order phase transition. The first order chiral phase transition line is determined by the difference of CJT effective actions.

hep-ph↗
arXiv2018

Geometric effects resulting from square and circular confinements for a particle constrained to a space curve

Investigating the geometric effects resulting from the detailed behaviors of the confining potential, we consider square and circular confinements to constrain a particle to a space curve. We find a torsion-induced geometric potential and a curvature-induced geometric momentum just in the square case, while a geometric gauge potential solely in the circular case. In the presence of electromagnetic field, a geometrically induced magnetic moment couples with magnetic field as an induced Zeeman coupling only for the circular confinement, also. As spin-orbit interaction is considered, we find some additional terms for the spin-orbit coupling, which are induced not only by torsion, but also curvature. Moreover, in the circular case, the spin also couples with an intrinsic angular momentum, which describes the azimuthal motions mapped on the space curve. As an important conclusion for the thin-layer quantization approach, some substantial geometric effects result from the confinement boundaries. Finally, these results are proved on a helical wire.

quant-ph↗
arXiv2018

Pion and kaon valence-quark quasiparton distributions

Algebraic Ansaetze for the Poincaré-covariant Bethe-Salpeter wave functions of the pion and kaon are used to calculate their light-front wave functions (LFWFs), parton distribution amplitudes (PDAs), quasi-PDAs (qPDAs), valence parton distribution functions (PDFs), and quasi-PDFs (qPDFs). The LFWFs are broad, concave functions; and the scale of flavour-symmetry violation in the kaon is roughly 15%, being set by the ratio of emergent masses in the $s$-and $u$-quark sectors. qPDAs computed with longitudinal momentum $P_z =1.75\,$GeV provide a semiquantitatively accurate representation of the objective PDA; but even with $P_z=3\,$GeV, they cannot provide information about this amplitude's endpoint behaviour. On the valence-quark domain, similar outcomes characterise qPDFs. In this connection, however, the ratio of kaon-to-pion $u$-quark qPDFs is found to provide a good approximation to the true PDF ratio on $0.3\lesssim x \lesssim 0.8$, suggesting that with existing resources computations of ratios of quasi-parton-distributions can yield results that support empirical comparison.

nucl-th↗
arXiv2018

Electromagnetic wave propagating along a space curve

Using the thin-layer approach, we derive the effective equation for the electromagnetic wave propagating along a space curve. We find intrinsic spin-orbit, extrinsic spin-orbit and extrinsic orbital angular momentum and intrinsic orbital angular momentum couplings induced by torsion, which can lead to geometric phase, spin and orbital Hall effects. And we show the helicity inversion induced by curvature that can convert the right-handed circularly polarized electromagnetic wave into left-handed polarized one, vice verse. Finally, we demonstrate that the gauge invariance of the effective dynamics is protected by the geometrically induced gauge potential.

physics.optics↗
arXiv2018

Finite volume effects with stationary wave solution from Nambu--Jona-Lasinio model

In this paper, we use the two-flavor Nambu-Jona-Lasinio (NJL) model with the proper time regularization to study the finite-volume effects of QCD chiral phase transition. Within a cubic volume of finite size $L$, we choose the stationary wave condition (SWC) as the real physical spatial boundary conditions of quark fields and compare our results with that by means of commonly used (anti-)period boundary condition (APBC or PBC). It is found that the results by means of SWC are obviously different to the results from the APBC or PBC. Although the three boundary conditions give the same chiral crossover transition curve in the infinite volume limit, the limit size $L_0$ (when $L\geq L_{0}$, the chiral quark condensate $-\left\langle { \bar ψψ} \right\rangle_L$ is indistinguishable from that at $L=\infty$) using SWC is $L_0\approx 500$ fm which is much larger than the results obtained using APBC or PBC. More importantly, $L_0\approx 500$ fm is also much large than the typical size of the quark-gluon plasma produced by the relativistic heavy ion collisions. This means that the finite volume effects play a very important role in Relativistic Heavy Ion Collisions. In addition, we also found that when $L\leq 2$ fm, even at zero temperature the chiral symmetry is effectively restored. Furthermore, to quantitatively reflect the finite volume effects on the QCD chiral phase transition, we introduce a new vacuum susceptibility, $χ_{1/L}(T)=-\frac{\partial \left\langle { \bar ψψ} \right\rangle}{\partial (1/L)}$. With this new vacuum susceptibility, it is very interesting to find $χ_{1/L}(T=0)=χ_{1/L}(T=1/L)$ for SWC.

hep-ph↗
arXiv2017

Dynamical study of $S$-wave $\bar{Q}Q\bar{q}q$ system

We perform the energy spectra calculating for the $S$-wave $\bar{Q}Q\bar{q}q$ (where $Q=c,b$ and $q=u,d,s$) system within two constituent quark models. The bound states of $B^*\bar{B}^*$ with $I(J^{PC})=1(0^{++}),~1(1^{+-}),~0(2^{++})$ and $B\bar{B}^*$ with isospin $I=1$, or $0$ are obtained in color-singlet-singlet channel. If considering the coupling of color channels, apart from the deep bound states appear in $[b\bar{q}]^{(*)}[q\bar{b}]^{(*)}$ scenario, a bound state $[c\bar{q}]^*[q\bar{c}]^*$ with $I(J^{PC})=1(0^{++})$ is also formed. The $B\bar{B}^*$ and the $B^*\bar{B}^*$ with quantum number $1(1^{+-})$ are well candidates for $Z_b^{\pm}(10610)$ and $Z_b^{\pm}(10650)$ reported by Belle collaboration respectively, while the $B\bar{B}^*$ with isospin $0$ can be interpret as a candidate for $Z_b^{0}(10610)$. A bound state $[c\bar{q}]^*[q\bar{c}]^*$ with $I(J^{PC})=1(0^{++})$ is comparable with $Z_c^{+}(4025)$ announced by BES.

hep-ph↗