arXiv subjects

Hong-Shi Zong

Publications and source records attributed to Hong-Shi Zong.

At least 19 recordsLinked to original sources

arXiv2022

Searching for Strange Quark Matter Objects Among White Dwarfs

The ground state of matter may be strange quark matter (SQM), not hadronic matter. A whole sequence of SQM objects, ranging from strange quark stars and strange quark dwarfs to strange quark planets, can stably exist according to this SQM hypothesis. A strange dwarf has a mass similar to that of a normal white dwarf but could harbor an extremely dense SQM core (with a density as large as $\sim \rm 4\times10^{14}\,g\,cm^{-3} $) at the center so that its radius can be correspondingly smaller. In this study, we try to search for strange dwarfs among the observed "white dwarfs" by considering their difference in the mass-radius relation. Seven strange dwarf candidates are identified in this way, whose masses are in the range of $\sim 0.02$ -- $0.12 M_{\odot}$, with the radii narrowly distributed in $\sim$ 9,000 -- 15,000 km. The seven objects are LSPM J0815+1633, LP 240-30, BD+20 5125B, LP 462-12, WD J1257+5428, 2MASS J13453297+4200437, and SDSS J085557.46+053524.5. Compared with white dwarfs of similar mass, these candidates are obviously smaller in radius. Further observations with large radio/infrared/optical telescopes on these interesting candidates are solicited.

astro-ph.SR↗

arXiv2021

Chiral symmetry restoration and properties of Goldstone bosons at finite temperature

We study chiral symmetry restoration by analyzing thermal properties of QCD's (pseudo-)Goldstone bosons, especially the pion. The meson properties are obtained from the spectral densities of mesonic imaginary-time correlation functions. To obtain the correlation functions, we solve the Dyson-Schwinger equations and the inhomogeneous Bethe-Salpeter equations in the leading symmetry-preserving rainbow-ladder approximation. In the chiral limit, the pion and its partner sigma degenerate at the critical temperature $T_c$. At $T \gtrsim T_c$, it is found that the pion rapidly dissociates, which signals deconfinement phase transition. Beyond the chiral limit, the pion dissociation temperature can be used to define the pseudo-critical temperature of chiral phase crossover, which is consistent with that obtained by the maximum point of the chiral susceptibility. The parallel analysis for kaon and pseudoscalar $s\bar{s}$ suggests that heavy mesons may survive above $T_c$.

hep-ph↗

arXiv2021

The light front wave functions and diffractive electroproduction of vector mesons

We determine the leading Fock-state light front wave functions (LF-LFWFs) of the $ρ$ and J/$ψ$ mesons, for the first time from the Dyson-Schwinger and Bethe-Salpeter equations (DS-BSEs) approach. A unique advantage of this method is that it renders a direct extraction of LF-LFWFs in presence of a number of higher Fock-states. Modulated by the current quark mass and driven by the dynamical chiral symmetry breaking (DCSB), we find the $ρ$ and $J/ψ$ LF-LFWFs different in profile, i.e., the former are broadly distributed in $x$ (the longitudinal light-cone momentum fraction of meson carried by quark) while the latter are narrow. Moreover, the $ρ$ LF-LFWFs contribute less than 50% to the total Fock-state normalization, suggesting considerable higher Fock-states in $ρ$. We then use these LF-LFWFs to study the diffractive $ρ$ and $J/ψ$ electroproduction within the dipole picture. The calculated cross section shows general agreement with HEAR data, except for growing discrepancy in $ρ$ production at low photon virtuality. Our work provides a first dipole picture analysis on diffractive $ρ$ electroproduction that confronts the parton nature of the light (anti)quarks.

hep-ph↗

arXiv2021

Finite-Size Effects with Boundary Conditions on Bose-Einstein Condensation

We investigate the statistical distribution for ideal Bose gases with constant particle density in the 3D box of volume $V=L^{3}$. By changing linear size $L$ and imposing different boundary conditions on the system, we present a numerical analysis on the characteristic temperature and condensate fraction, and find that the smaller linear size is efficient to increase the characteristic temperature and condensate fraction. Moreover, there is a singularity under the antiperiodic boundary condition.

cond-mat.quant-gas↗

arXiv2021

The chiral phase transition and equation of state in the chiral imbalance

The chiral phase transition and equation of state are studied within a new self-consistent mean-field approximation of the two-flavor Nambu$-$Jona-Lasinio model. In this newly developed model, modifications to the chemical potential $μ$ and chiral chemical potential $μ_5$ is naturally included by adding vector and axial-vector channels from Fierz-transformed Lagrangian to the standard Lagrangian. In proper-time scheme, the chiral phase transition is a crossover in the $T-μ$ plane. But when $μ_5$ is increased, our study shows that there may exist first order phase transition. Furthermore, the chiral imbalance will soften the equation of state of quark matter. The mass-radius relations and tidal deformability of quark stars are calculated. As $μ_5$ increases, the maximum mass and radius decrease. The vector channel and axial-vector channel have opposite influence on the equation of state. However, when EOS is constrained by astronomical observations, the shape of the mass-radius curve can be used to determine whether there is chiral imbalance in the dense object, and thus indirectly proving the CP violation in the dense matter. Our study shows a different influence of the chiral imbalance on the chiral phase transition in contrary to tree-momentum-cutoff scheme.

nucl-th↗

arXiv2020

Chiral phase transition inside a rotating cylinder within the Nambu--Jona-Lasinio model

We study the chiral phase transition inside a rotating cylinder within the framework of the Namb--Jona-Lasinio model. A spectral boundary condition is imposed to avoid faster than light. We investigate how the geometry of the cylinder and rotation influence the chiral phase transition at finite temperature and chemical potential. The inhomogeneous effects caused by the finite size and rotation are also taken into account. It is found that finite size will reduce the chiral transition temperature and raises the chiral transition chemical potential, while the rotation reduces both the chiral transition temperature and chemical potential. In addition, we discuss the implications of our results in heavy-ion collisions and equation of states of neutron star.

hep-ph↗

arXiv2020

Geometry induced quantum Hall effect and Hall viscosity

For a particle confined to the two-dimensional helical surface embedded in four-dimensional (4D) Euclidean space, the effective Hamiltonian is deduced in the thin-layer quantization formalism. We find that the gauge structure of the effective dynamics is determined by torsion, which plays the role of U(1) gauge potential, and find that the topological structure of associated states is defined by orbital spin which originates from 4D space. Strikingly, the response to torsion contributes a quantum Hall effect, and the response to the deformation of torsion contributes Hall viscosity that is perfectly presented as a simultaneous occurrence of multiple channels for the quantum Hall effect. This result directly provides a way to probe Hall viscosity.

cond-mat.mes-hall↗

arXiv2020

QCD phase diagram at finite isospin and baryon chemical potentials with the self-consistent mean field approximation

The self-consistent mean field approximation of two-flavor NJL model with introducing a free parameter $α$ to reflect the competition between "direct" channel and the "exchange" channel, is employed to study QCD phase structure at finite isospin chemical potential $μ_I$, finite baryon chemical potential $μ_B$ and finite temperature $T$, especially the location of the QCD critical point. It is found that, for fixed isospin chemical potentials the lower temperature of phase transition is obtained with $α$ increasing in the $T-μ_I$ plane, and the largest difference of the phase transition temperature with different $α$'s appears at $μ_I \sim 1.5m_π$. At $μ_I=0$ the temperature of the QCD critical end point (CEP) decreases with $α$ increasing, while the critical baryon chemical potential increases. At high isospin chemical potential ($μ_I=500$ MeV), the temperature of the QCD tricritical point (TCP) increases with $α$ increasing, and in the regions of low temperature the system will transit from pion superfluidity phase to the normal phase as $μ_B$ increases. At low temperatures, the critical temperature of QCD phase transition with different $α$'s rapidly increases with $μ_I$ at the beginning, and then increases smoothly around $μ_I>300$ MeV. In high baryon density region, the increase of the isospin chemical potential will raise the critical baryon chemical potential of phase transition.

nucl-th↗

arXiv2020

Chiral crossover transition from the Dyson-Schwinger equations in a sphere

Within the framework of Dyson--Schwinger equations of QCD, we study the effect of finite volume on the chiral phase transition in a sphere with the MIT boundary condition. We find that the chiral quark condensate $\langle\barψ ψ\rangle$ and pseudotransition temperature $T_{pc}$ of the crossover decreases as the volume decreases, until there is no chiral crossover transition at last. We find that the system for $R = \infty $\ fm is indistinguishable from $R=10$ fm and there is a significant decrease in $T_{pc}$ with $R$ as $R<4$ fm. When $R<1.5$ fm, there is no chiral transition in the system.

nucl-th↗

arXiv2020

Identifying the nature of the QCD transition in heavy-ion collisions with deep learning

In this proceeding, we review our recent work using deep convolutional neural network (CNN) to identify the nature of the QCD transition in a hybrid modeling of heavy-ion collisions. Within this hybrid model, a viscous hydrodynamic model is coupled with a hadronic cascade "after-burner". As a binary classification setup, we employ two different types of equations of state (EoS) of the hot medium in the hydrodynamic evolution. The resulting final-state pion spectra in the transverse momentum and azimuthal angle plane are fed to the neural network as the input data in order to distinguish different EoS. To probe the effects of the fluctuations in the event-by-event spectra, we explore different scenarios for the input data and make a comparison in a systematic way. We observe a clear hierarchy in the predictive power when the network is fed with the event-by-event, cascade-coarse-grained and event-fine-averaged spectra. The carefully-trained neural network can extract high-level features from pion spectra to identify the nature of the QCD transition in a realistic simulation scenario.

nucl-th↗

arXiv2020

Rotating fermions inside a spherical boundary

We apply the cannonical quantization procedure to the Dirac field inside a spherical boundary with rotating coordinates. The rotating quantum states with two kinds of boundary conditions, namely, spectral and MIT boundary conditions, are defined. To avoid faster-than-light, we require the speed on the surface to be less than the speed of light. For this situation, the definition of vacuum is unique and identical with the Minkowski vacuum. Finally, we calculate the thermal expectation value of the fermion condensate in a thermal equilibrium rotating fermion field and find it depends on the boundary condition.

math-ph↗

arXiv2020

Identifying the nature of the QCD transition in relativistic collision of heavy nuclei with deep learning

Using deep convolutional neural network (CNN), the nature of the QCD transition can be identified from the final-state pion spectra from hybrid model simulations of heavy-ion collisions that combines a viscous hydrodynamic model with a hadronic cascade "after-burner". Two different types of equations of state (EoS) of the medium are used in the hydrodynamic evolution. The resulting spectra in transverse momentum and azimuthal angle are used as the input data to train the neural network to distinguish different EoS. Different scenarios for the input data are studied and compared in a systematic way. A clear hierarchy is observed in the prediction accuracy when using the event-by-event, cascade-coarse-grained and event-fine-averaged spectra as input for the network, which are about 80%, 90% and 99%, respectively. A comparison with the prediction performance by deep neural network (DNN) with only the normalized pion transverse momentum spectra is also made. High-level features of pion spectra captured by a carefully-trained neural network were found to be able to distinguish the nature of the QCD transition even in a simulation scenario which is close to the experiments.

hep-ph↗

arXiv2020

Chiral phase transition in a rotating sphere

We study the chiral phase transition of the two-flavor Nambu-Jona-Lasinio (NJL) model in a rotating sphere, which includes both rotation and finite size effects. We find that rotation leads to a suppression of the chiral condensate at a finite temperature, while its effects are smaller than the finite size effects. Our work can be helpful to study the effects relevant to rotation in heavy-ion collisions in a more realistic way.

nucl-th↗

arXiv2020

Chiral transition and the chiral charge density of the hot and dense QCD matter

We study the chirally imbalanced hot and dense strongly interacting matter by means of the Dyson-Schwinger equations (DSEs). The chiral phase diagram is studied in the presence of chiral chemical potential $μ_5$. The chiral quark condensate $\langle \barψ ψ\rangle$ is obtained with the Cornwall-Jackiw-Tomboulis (CJT) effective action in concert with the Rainbow truncation. Catalysis effect of dynamical chiral symmetry breaking (DCSB) by $μ_5$ is observed. We examine with two popular gluon models and consistency is found within the DSE approach, as well as in comparison with lattice QCD. The CEP location $(μ_E,T_E)$ shifts toward larger $T_E$ but constant $μ_E$ as $μ_5$ increases. A technique is then introduced to compute the chiral charge density $n_5$ from the fully dressed quark propagator. We find the $n_5$ generally increases with temperature $T$, quark number chemical potential $μ$ and $μ_5$. Since the chiral magnetic effect (CME) is typically investigated with peripheral collisions, we also investigate the finite size effect on $n_5$ and find an increase in $n_5$ with smaller system size.

hep-ph↗

arXiv2020

Exploring hybrid equation of state with constraints from tidal deformability of GW170817

With a interpolation method on the P-$μ$ plane, a hybrid equation of state is explored. The quark phase is described by our newly developed self-consistent two-flavor Nambu$-$Jona-Lasinio model. It retains the contribution from the vector channel in the Fierz-transformed Lagrangian by introducing a weighting parameter $α$ [Chin. Phys. C \textbf{43}, 084102 (2019)]. In the hadron phase we use the relativistic mean-field theory. We study the dependence of hybrid EOS and mass-radius relation on $α$. It is found that increasing $α$ makes the hybrid EOS softer in the medium pressure. We can get stellar mass larger than $2M_\odot$. Further, we calculate the tidal deformability $\tildeΛ$ for binary stars and compare with recent analysis GW170817 [Phys. Rev. X \textbf{9}, 011001 (2019)].

hep-ph↗

arXiv2020

Transverse Ward-Takahashi Identities and Full Vertices Functions in Different Representation in QED$_3$

We first derive the transverse Ward-Takahashi identities (WTI) of 3-dimensional quantum electrodynamics (QED$_3$) by means of the canonical quantization method and the path integration method, and then prove for the first time that QED$_3$ is strictly solvable based on the transverse WTI and the longitudinal WTI, that is, the full vector and tensor vertices functions can be expressed in term of the fermion propagators in QED$_3$. Further, we discuss the effect of different $γ$ matrix representations on the full fermion-boson vertex function. It is found that the full vector vertex function does not depend on the different $γ$ matrix representation we use, \textit{i.e.}, it does not depend on whether we use 4 $\times$ 4 representation or 2 $\times$ 2 representation. But the tensor vertex function depends on the representation we use.

hep-th↗

arXiv2020

Semileptonic decays of $D_{(s)}$ mesons

A symmetry-preserving continuum approach to meson bound-states in quantum field theory, employed elsewhere to describe numerous $π$- and $K$-meson electroweak processes, is used to analyse leptonic and semileptonic decays of $D_{(s)}$ mesons. Each semileptonic transition is conventionally characterised by the value of the dominant form factor at $t=0$ and the following results are obtained herein: $f_+^{D_s\to K}(0) = 0.673(40)$; $f_+^{D\to π}(0)=0.618(31)$; and $f_+^{D\to K}(0)=0.756(36)$. Working with the computed $t$-dependence of these form factors and standard averaged values for $|V_{cd}|$, $|V_{cs}|$, one arrives at the following predictions for the associated branching fractions: ${\cal B}_{D_s^+\to K^0 e^+ ν_e} = 3.31(33)\times 10^{-3}$; ${\cal B}_{D^0\to π^- e^+ ν_e} = 2.73(22)\times 10^{-3}$; and ${\cal B}_{D^0\to K^- e^+ ν_e} = 3.83(28)$%. Alternatively, using the calculated $t$-dependence, agreement with contemporary empirical results for these branching fractions requires $|V_{cd}|=0.221(9)$, $|V_{us}|=0.953(34)$. With all $D_{(s)}$ transition form factors in hand, the nature of SU$(3)$-flavour symmetry-breaking in this array of processes can be analysed; and just as in the $π$-$K$ sector, the magnitude of such effects is found to be determined by the scales associated with emergent mass generation in the Standard Model, not those originating with the Higgs mechanism.

hep-ph↗

arXiv2020

Strange quark stars within proper time regularized (2+1)-flavor NJL model

In this work we use the equation of state (EOS) of (2+1)-flavor Nambu-Jona-Lasinio (NJL) model to study the structure of the strange quark star. With a new free parameter $α$, the Lagrangian is constructed by two parts, the original NJL Lagrangian and the Fierz transformation of it, as $\mathcal{L}=(1-α)\mathcal{L}_{NJL}+α\mathcal{L}_{Fierz}$. To determine the range of $α$, we compare the binding energies in the 2-flavor and (2+1)-flavor cases. We also consider the constraints of chemical equilibrium and electric charge neutrality in the strange quark star and choose six representative EOSs with different $α$ and $B$ (bag constant) to study their influence on the structure of the strange quark star. As a result, we find that a larger $α$ and a smaller $B$ corresponds to a heavier star with a stiffer EOS. Furthermore, the heaviest strange quark star is in agreement with not only the recent mass observation of PSR J0740+6620 and the X-ray observations on radius measurements, but also the constraint on tidal deformability of GW170817.

hep-ph↗