arXiv subjects

Jingyi Chao

Publications and source records attributed to Jingyi Chao.

At least 19 recordsLinked to original sources

arXiv2026

Mass spectra of charged mesons and the quenching of vector meson condensation via exact phase-space diagonalization

We investigate the dynamics and mass spectra of charged pseudoscalar ($\pi^+$) and vector ($\rho^+$) mesons in a background magnetic field at finite temperature using the two-flavor Nambu-Jona--Lasinio (NJL) model. By employing a quark propagator that isolates the Schwinger phase from its Landau level expansion, we formulate an exact non-commutative phase-space framework utilizing the Wigner-Weyl transform and the Moyal star product. This approach enables the algebraic diagonalization of the Bethe-Salpeter equations for composite states with asymmetric fractional constituent charges. For the pseudoscalar channel, we analytically verify the exact cancellation between the dynamical random phase approximation spatial sum rules and the vacuum gap equation. This identity preserves the generalized Goldstone theorem, causing the $\pi^+$ pole mass to strictly track the kinematic zero-point energy drift at order of $eB$. In the vector channel, our full phase-space evaluation reveals that the Zeeman spin-splitting emerges dynamically from microscopic threshold truncations governed by the chiral Dirac algebra. Notably, we find that the tachyonic instability of the spin-aligned $\rho^+$ state is quenched. The magnetic catalysis of the chiral condensate drives the continuum threshold ($2M$) upwards, overtaking the Zeeman attraction and preventing vector meson condensation within this mean-field framework. Furthermore, finite-temperature evaluations show a monotonic thermal suppression of the meson masses driven by Pauli blocking, yet all modes remain bound without undergoing Mott dissociation prior to chiral symmetry restoration.

hep-ph↗

arXiv2024

Neutral pion masses within a hot and magnetized medium in a lattice-improved soft-wall AdS/QCD model

We investigate chiral phase transitions and the screening masses, pole masses, and thermal widths of neutral pion meson with finite temperature $T$ and magnetic field $B$ in a lattice-improved AdS/QCD model, which is constructed by fitting the lattice results of the pseudo-critical temperatures ( T_{\text{pc}}(B) ). Specifically, we have that the chiral condensate (σ) undergoes a crossover phase transition demonstrating distinct magnetic catalysis and inverse magnetic catalysis effects in very low and high-temperature regions with fixed finite $B$, respectively. For the screening masses, we find that the longitudinal component decreases with $B$ at very low and high temperatures and increases with $B$ near $T_{\text{pc}}$. The transverse component always increases with $B$ at fixed $T$. However, both the longitudinal and transverse screening masses increase with $T$ at fixed $B$. Furthermore, we find that the pole mass decreases with the increasing of $B$ or $T$. Besides, it is interesting to note that the thermal width shows similar behavior to the longitudinal screening masses in the very high temperature region.

hep-th↗

arXiv2023

Diquark and chiral condensate in a self-consistent NJL-type model

In this work, a modified two-flavor NJL-type model is utilized, in which the contact current-current interaction is Fierz-transformed into quark-antiquark interactions and quark-quark interactions, which are directly related to the chiral condensate and diquark condensate, respectively. Under mean-field approximation, the chiral condensate and the diquark condensate are studied on the same footing. We discuss in detail the competition between the chiral condensate and the diquark condensate, which are exclusively paired with u and d quarks, while also investigating the order of the chiral phase transition through an analysis of the resulting chiral susceptibility.

hep-ph↗

arXiv2023

N-particle irreducible actions for stochastic fluids

We construct one- and two-particle irreducible (1PI and 2PI) effective actions for the stochastic fluid dynamics of a conserved density undergoing diffusive motion. We compute the 1PI action at one-loop order, and the 2PI action in two-loop approximation. We derive a set of Schwinger-Dyson equations, and regularize the resulting equations using Pauli-Villars fields. We numerically solve the Schwinger-Dyson equations for a non-critical fluid. We find that higher-loop effects summed by the Schwinger-Dyson renormalize the non-linear coupling. We also find indications of a diffuson-cascade, the appearance $n$-loop corrections with smaller and smaller exponential suppression.

hep-ph↗

arXiv2023

Dimensional reduction and the generalized pion in a magnetic field within the NJL model

In this work, the mass of the neutral pion is investigated in the presence of background magnetic fields in the framework of the Nambu--Jona-Lasinio model. Taking into account the anisotropic four-fermion interactions, a tensor current arises in the magnetized QCD system, which forms an anomalous magnetic moment (AMM) coupling in the Dirac equation for the quarks. By solving the gap equations, we find that the sign of the dynamically generated AMM is opposite to the sign of the quark's charge and its magnitude is definitely smaller than the constituent mass. We construct two generalized Nambu-Goldstone pions, which emerge as combinations of the quantum fluctuations around the conventional scalar and the emergent tensor chiral condensates. We analytically demonstrate that the Goldstone nature has been spoiled by the dimensional reduction in the two-particle state and the corresponding decreasing mass of the lighter generalized pionic mode is a remnant of the infrared dynamics.

hep-ph↗

arXiv2023

Non-equilibrium cumulants within model A from crossover to first-order phase transition side

We study the non-equilibrium cumulants of the chiral order parameter field (σ field) in different phase transition scenarios via Langevin dynamics. Cumulants up to fourth-order have been calculated based on the spacetimedependent σ configurations from the event-by-event numerical simulations. By limiting the cooling of the system in a Hubble-like way, the out-of-equilibrium cumulants illustrate clear memory effects during the evolution. Both the signs and the magnitudes of the high-order cumulants differ from the equilibrium ones below the phase transition temperature. Especially, the dynamical cumulants grow more intensively from the first-order phase transition side than they do from the crossover side. In addition, analysis of the high-order offequilibrium cumulants on the hypothetical freeze-out lines present non-monotonic curves in the large chemical potential region.

nucl-th↗

arXiv2023

Thermalization and prethermalization in the soft-wall AdS/QCD model

The real-time dynamics of chiral phase transition is investigated in a two-flavor ($N_f=2$) soft-wall AdS/QCD model. To understand the dynamics of thermalization, we quench the system from initial states deviating from the equilibrium states. Then, we solve the nonequilibrium evolution of the order parameter (chiral condensate $\langle σ\equiv\bar{q}q\rangle$). It is shown that the system undergoes an exponential relaxation at temperatures away from the critical temperature $T_c$. The relaxation time diverges at $T_c$, presenting a typical behavior of critical slowing down. Numerically, we extract the dynamic critical exponent $z$, and get $z\approx 2$ by fitting the scaling behavior $σ\propto t^{-β/(νz)}$, where the mean-field static critical exponents (order parameter critical exponent $β=1/2$, correlation length critical exponent $ν=1/2$ ) have been applied. More interestingly, it is remarked that, for a large class of initial states, the system would linger over a quasi-steady state for a certain period of time before the thermalization. It is suggested that the interesting phenomenon, known as prethermalization, has been observed in the framework of holographic models. In such prethermal stage, we verify that the system is characterized by a universal dynamical scaling law and described by the initial-slip exponent $θ=0$.

hep-ph↗

arXiv2022

Exposing the effect of $p$-wave in pion triplet under the strong magnetic field

The static properties, masses and decay constants, of pseudoscalar meson triplet in a strongly magnetized medium are studied through the Dyson-Schwinger equation approach treatment of a contact interaction. Complementary to the usual vector-vector form, a symmetry-preserving formulation of couplings has been proposed in this work, without modifying the quark propagator, to control the strength of the $p$-wave component of Bethe-Salpeter amplitude. It is found that, with the help of flexible auxiliary interaction, our simple model is able to reproduce the observation in the lattice QCD simulation, where the spectra of the charged pseudo-scalar meson shows a non-monotonic behavior as the magnetic field grows. The discovery of this work implies the strong magnetic field affects the inner structure of mesons dramatically.

hep-ph↗

arXiv2021

Light charged pion in ultra-strong magnetic field

In this work, the mass of charged pions is investigated in the presence of background magnetic fields stronger than the energy scale of QCD. We introduce an anomaly magnetic momentum term in the Dirac equation and obtain the quark propagator as consequence. We find a novel finite Landau level, denoted as $tl$LL, becoming dominant rather than the conventional lowest Landau level. We examine that, due to the shifting of Landau level, it drives a mass decreasing around $eB\sim 0.8~\mathrm{GeV}^2$ for charged pions and their masses drastically limit to the neutral one at ultra-strong magnetic field, $eB\sim 1.6~\mathrm{GeV}^2$, which is consistent with the recent lattice simulation.

hep-ph↗

arXiv2021

Application of radial basis functions neutral networks in spectral functions

The reconstruction of spectral function from correlation function in Euclidean space is a challenging task. In this paper, we employ the Machine Learning techniques in terms of the radial basis functions networks to reconstruct the spectral function from a finite number of correlation data. To test our method, we first generate one type of correlation data using a mock spectral function by mixing several Breit-Wigner propagators. We found that compared with other traditional methods, TSVD, Tikhonov, and MEM, our approach gives a continuous and unified reconstruction for both positive definite and negative spectral function, which is especially useful for studying the QCD phase transition. Moreover, our approach has considerably better performance in the low frequency region. This has advantages for the extraction of transport coefficients which are related to the zero frequency limit of the spectral function. With the mock data generated through a model spectral function of stress energy tensor, we find our method gives a precise and stable extraction of the transport coefficients.

hep-ph↗

arXiv2021

Effect of the anomalous magnetic moment of quarks on magnetized QCD matter and meson spectra

We systematically investigate the effect of the anomalous magnetic moment(AMM) of quarks on the magnetized QCD matter, including the magnetic susceptibility, the inverse magnetic catalysis around the critical temperature and the neutral/charged pion and rho meson spectra under magnetic fields. The dynamical AMM of quarks, its coupling with magnetic field causes Zeeman splitting of the dispersion relation of quarks thus changes the magnetism properties and meson mass spectra under magnetic fields. It is found that including the AMM of quarks cannot fully understand lattice results of the magnetized matter: The AMM of quarks reduces the dynamical quark mass thus causes the inverse magnetic catalysis around $T_c$. The neutral pion mass is very sensitive to the AMM, it decreases with magnetic field quickly, and the charged pion mass shows a nonlinear behavior, i.e., firstly linearly increases with the magnetic field and then saturates at strong magnetic field. For rho meson, it is observed that AMM reduces the mass of neutral rho meson mass with different $s_z$, and reduces the mass of $s_z=+1,0$ component charged rho meson mass but enhances the $s_z=-1$ component charged rho meson mass. The magnetic susceptibility at low temperature can be either positive or negative with different AMM.

hep-ph↗

arXiv2020

Multiplicative noise and the diffusion of conserved densities

Stochastic fluid dynamics governs the long time tails of hydrodynamic correlation functions, and the critical slowing down of relaxation phenomena in the vicinity of a critical point in the phase diagram. In this work we study the role of multiplicative noise in stochastic fluid dynamics. Multiplicative noise arises from the dependence of transport coefficients, such as the diffusion constants for charge and momentum, on fluctuating hydrodynamic variables. We study long time tails and relaxation in the diffusion of a conserved density (model B), and a conserved density coupled to the transverse momentum density (model H). Careful attention is paid to fluctuation-dissipation relations. We observe that multiplicative noise contributes at the same order as non-linear interactions in model B, but is a higher order correction to the relaxation of a scalar density and the tail of the stress tensor correlation function in model H.

hep-th↗

arXiv2020

Mass-dependence of pseudocritical temperature in mean field approximation

We restrict our computation in the mean field approximation which could lead to a clear critical behavior. We analyze the scaling behavior with different shape of interaction kernel by considering different dressed-gluon models. The critical exponent we obtained is consistent with that in the $3D$ $\textrm{O}(4)$ universality class. The size of critical region is up to $m_{0}^{} \le 2\sim 4\;$MeV in this mean field approximation which sets naturally an upper bound of the critical region since the fluctuations beyond mean-field usually diminish the critical region. Besides, we analyze the possible percentage of the maximum chiral susceptibility and pion mass range at which the chiral phase transition temperature is independent of the current quark mass. The results show that the percentage and the pion mass range depend on the details of interaction kernel, which differs in gluon models.

hep-ph↗

arXiv2018

Phase diagram of two-color QCD matter at finite baryon and axial isospin densities

We study the two-color QCD matter within two fundamental quark flavors via both chiral perturbation theory and Nambu--Jona-Lasinio model methods. The effective Lagrangian described by low lying meson and baryon, i.e., diquark, is derived, where the excitations locate in the extended $\mathrm{SU}(4)$ flavor symmetry space. We determine the leading order terms on the dependence of the baryon and axial isospin densities. Then, the two-color NJL model is employed to run the numerical simulation and the phase diagram in the plane of $μ-ν_{5}$ is plotted.

hep-ph↗

arXiv2018

Charged pion condensation under parallel electromagnetic fields

The formation of charged pion condensate under parallel electromagnetic fields is studied within the two-flavor Nambu--Jona-Lasinio model. The technique of Schwinger proper time method is extended to explore the quantity locating in the off-diagonal flavor space, i.e., charged pion. We obtain the associated effective potential as a function of the strength of the electromagnetic fields and find out that it contains a sextic term which possibly induce weakly first order phase transition. Dependence of pion condensation on model parameters is investigated.

hep-ph↗

arXiv2016

Photon polarization tensor in a magnetized plasma system

We investigate the photon polarization tensor at finite temperature in the presence of a static and homogeneous external magnetic field. In our scheme, the Matsubara frequency summation is performed after Poisson summation, which will be taken easily and convergent quickly in the frame of proper time representation. Moreover, the dependence of Landau levels is expressed explicitly. It demonstrates the convergence of summing Landau levels as it has to be. Consequently, there is no necessary to truncate the Landau level in a numerical estimation. At zero temperature, the Lowest Landau Level (LLL) approximation is analytically satisfied for the imaginary parts of the vacuum photon polarization tensor. Our results examine that, the LLL approximation is not enough for the thermal photon polarization tensor, it gains the contribution not only from the lowest Landau level but also up to the finite-$n$ levels. Such large imaginary ones only show up at finite temperatures, which is the so called Landau damping. It originates from the absorption of soft fields by hard plasma constituents, which is a universal feature of plasma systems. Finally, it was argued that the summation of Matsubara frequency is not commuted with Landau level ones, such conjecture is excluded in our calculations.

hep-ph↗

arXiv2014

Zeta Function Regularization of Photon Polarization Tensor for a Magnetized Vacuum

In this paper, we have developed a systematic technique to regularize double summations of Landau levels and analytically evaluated the photon vacuum polarization at an external magnetic field. The final results are described by Lerch transcendent $Φ(z,s,v)$ or its $z$-derivation. We have found that the tensor of vacuum polarization is split into not only longitudinal and transverse parts but also another mixture component. We have obtained a complete expression of the magnetized photon vacuum polarization at any kinematic regime and any strength of magnetic field for the first time. In the weak $B$-fields, after canceling out a logarithmic counter term, all three scalar functions are limited to the usual photon polarization tensor without turning on magnetic field. In the strong $B$-fields, the calculations under Lowest Landau Level approximation are only valid at the region $M^2\gg q_{\shortparallel}^2$, but not correct while $q_{\shortparallel}^2\gg M^2$, where, an imaginary part has been missed. It reminds us, a recalculation of the gap equation under a full consideration of all Landau Levels is necessary in the next future.

hep-th↗

arXiv2013

Inverse magnetic catalysis induced by sphalerons

The recently discovered inverse magnetic catalysis around the critical temperature indicates that some important information is missing in our current understanding of conventional chiral dynamics of QCD, which is enhanced by the magnetic field. In this work, we provide a mechanism to explain that the inverse magnetic catalysis around the critical temperature is induced by sphalerons. At high temperatures, sphaleron transitions between distinct classical vacua cause an asymmetry between the number of right- and left-handed quarks due to the axial anomaly of QCD. In the presence of a strong magnetic field, the chiral imbalance is enhanced and destroys the right- and left-handed pairings, which naturally induces a decreasing critical temperature of the chiral phase transition for increasing magnetic field. The inverse magnetic catalysis at finite baryon density, and the critical end point in the presence of a strong magnetic field is also explored in this work.

hep-ph↗