arXiv subjects

De-fu Hou

Publications and source records attributed to De-fu Hou.

At least 19 recordsLinked to original sources

arXiv2026

Heavy quark collisional energy loss in a nonextensive quark-gluon plasma

In this study, we derive the longitudinal and transverse gluon self-energies and the corresponding dielectric functions for a nonextensive QGP, based on nonextensive statistical mechanics and a kinetic theory framework. The nonextensive parameter $q$ enters these quantities primarily through the modification of the Debye mass. Utilizing the derived dielectric functions, we then calculate the collisional energy loss for a heavy quark using two established formalisms: the plasma physics-based Thoma-Gyulassy formula and the thermal field theory-originated Kirzhnits-Thoma formula. Our results show that for both formalisms, the collisional energy loss increases with the nonextensive parameter $q$ with this enhancement being more significant at higher incident quark momenta and suppressed for a heavier quark mass. The energy loss predicted from the Kirzhnits-Thoma formula is substantially larger than that from the Thoma-Gyulassy formula, and the nonextensive effect on the energy loss is more pronounced in the former. Furthermore, the mass suppression of the nonextensive effect on the energy loss is weaker in the Kirzhnits-Thoma approach. These calculations demonstrate that nonextensive statistics can significantly alter the energy loss in the QGP.

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arXiv2025

Electromagnetic responses of a non-extensive quark-gluon plasma

Based on the non-extensive statistical mechanics and the gluon polarization tensor obtained from kinetic theory, we derive the longitudinal and transverse gluon self-energies for the quark-gluon plasma. The electric permittivity $\varepsilon$ and the magnetic permeability $μ_M$ are evaluated from the gluon self-energies through which the real part of the square of the refraction index ${\rm Re}\, n^2$ and the Depine-Lakhtakia index $n_{DL}$ are investigated. The real part of $\varepsilon$ displays a frequency pole $ω_d=p$, which is just the position of the frequency inflexion of the imaginary part of $\varepsilon$. The non-extensive parameter $q$ significantly affects the real and imaginary parts of $\varepsilon$ in the space-like region $ω<p$, while the frequency pole $ω_d=p$ remains unchanged as $q$ increases. The magnetic permeability, ${\rm Re}\, n^2$ and the Depine-Lakhtakia index $n_{DL}$ diverge at frequency $ω_m$. As $q$ increases, the pole frequency $ω_m$ shifts to large frequency region. The Depine-Lakhtakia index $n_{DL}$ becomes negative in a quite large frequency region $ω\in[ω_c, ω_m]$. When $q$ increases, the frequency range for $n_{DL}<0$ becomes wider. Nevertheless, there are no propagating modes for the negative refraction. In addition, as momentum $p$ increases, the electric permittivity, the magnetic permeability, ${\rm Re}\, n^2$ and $n_{DL}$ are sensitive to the change of $p$, which indicates the importance of the spatial dispersion in the electromagnetic responses of the QGP.

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arXiv2024

Heavy quarkonium spectral function in an anisotropic background

In this paper, we use a five-dimensional Einstein-dilaton-two-Maxwell holographic QCD model to investigate the dissociation effects of $J/Ψ$ and $Υ(1S)$ states in an anisotropic medium by calculating their spectral functions. First, we present the holographic quarkonium masses at zero temperature via Physics-Informed Neural Networks. Then, at finite temperature, we derive the spectral functions, representing heavy vector mesons as peaks, and observe that with increasing anisotropy, temperature, chemical potential, and warp factor, the peak height diminishes while its width expands, indicating an accelerated dissociation process. Additionally, the results indicate the anisotropy induces a stronger dissociation effect in the direction parallel to the polarization compared to the perpendicular, revealing the anisotropy's directional influence.

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arXiv2021

Chiral Magnetic Effect and Three-point Function from AdS/CFT Correspondence

The chiral magnetic effect with a fluctuating chiral imbalance is more realistic in the evolution of quark-gluon plasma, which reflects the random gluonic topological transition. Incorporating this dynamics, we calculate the chiral magnetic current in response to space-time dependent axial gauge potential and magnetic field in AdS/CFT correspondence. In contrast to conventional treatment of constant axial chemical potential, the response function here is the AVV three-point function of the $\mathcal{N}=4$ super Yang-Mills at strong coupling. Through an iterative solution of the nonlinear equations of motion in Schwarzschild-AdS$_5$ background, we are able to express the AVV function in terms of two Heun functions and prove its UV/IR finiteness, as expected for $\mathcal{N}=4$ super Yang-Mills theory. We found that the dependence of the chiral magnetic current on a non-constant chiral imbalance is non-local, different from hydrodynamic approximation, and demonstrates the subtlety of the infrared limit discovered in field theoretic approach. We expect our results enrich the understanding of the phenomenology of the chiral magnetic effect in the context of relativistic heavy ion collisions.

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arXiv2021

Color-electric conductivity in a viscous quark-gluon plasma

Several different transport processes, such as heat transport, momentum transport and charge transport, may take place at the same time in the quark-gluon plasma (QGP). The corresponding transport coefficients are heat conductivity, shear viscosity and electric conductivity respectively. In the present paper, we will study the color-electric conductivity of the QGP in presence of shear viscosity, which is focused on the connection between the charge transport and the momentum transport. To achieve that goal, we solve the viscous chromohydrodynamic equations which are obtained from the QGP kinetic theory associated with the distribution function modified by shear viscosity. According to the solved color fluctuations of hydrodynamic quantities we obtain the induced color current through which the color-electric conductivity is derived. Then we study viscous effects on the color-electric conductivity. In the viscous chromohydrodynamic approach, the conductivity properties of the QGP are mainly demonstrated by the longitudinal part of the color-electric conductivity. Shear viscosity has an appreciable impact on real and imaginary parts of the color-electric conductivity in some frequency region.

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arXiv2020

The noncommutativity of the static and homogeneous limit of the axial chemical potential in chiral magnetic effect

We study the noncommutativity of different orders of zero energy-momentum limit pertaining to the axial chemical potential in the chiral magnetic effect. While this noncommutativity issue originates from the pinching singularity at one-loop order, it cannot be removed by introducing a damping term to the fermion propagators. The physical reason is that modifying the propagator alone would violate the axial-vector Ward identity and as a result a modification of the longitudinal component of the axial-vector vertex is required, which contributes to CME. The pinching singularity with free fermion propagators was then taken over by the singularity stemming from the dressed axial-vector vertex. We show this mechanism by a concrete example. Moreover, we proved in general the vanishing CME in the limit order that the static limit was taken prior to the homogeneous limit in the light of Coleman-Hill theorem for a static external magnetic field. For the opposite limit that the homogeneous limit is taken first, we show that the nonvanishing CME was a consequence of the nonrenormalizability of chiral anomaly for an arbitrary external magnetic field.

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arXiv2020

Potential analysis of holographic Schwinger effect in the magnetized background

We study the holographic Schwinger effect with magnetic field at RHIC and LHC energies by using the AdS/CFT correspondence. We consider both weak and strong magnetic field cases with $B\ll T^2$ and $B\gg T^2$ solutions respectively. Firstly, we calculate separating length of the particle pairs at finite magnetic field. It is found that for both weak and strong magnetic field solutions the maximum value of separating length decreases with the increase of magnetic field , which can be inferred that the virtual electron-positron pairs become real particles more easily. We also find that the magnetic field reduces the potential barrier and the critical field for the weak magnetic field solution, thus favors the Schwinger effect. With strong magnetic field solution, the magnetic field enhances the Schwinger effect when the pairs are in perpendicular to the magnetic field although the magnetic field increases the critical electric field.

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arXiv2020

Effect of gluon condensate on holographic Schwinger effect

We perform the potential analysis in holographic Schwinger effect in a deformed anti-de Sitter (AdS) background with backreaction due to the gluon condensate. We determine the potential by analyzing the classical string action attaching on a probe D3-brane sitting at an intermediate position in the bulk AdS space. It is found that the inclusion of the gluon condensate reduces the production rate, reverse to the effect of the temperature. Also, we evaluate the critical electric field by Dirac-Born-Infeld (DBI) action.

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arXiv2019

1+1 dimensional relativistic magnetohydrodynamics with longitudinal acceleration

Non-central heavy-ion collisions generate the strongest magnetic field of the order of $10^{18}-10^{19}$ Gauss due to the electric current produced by the positively charged spectators that travel at nearly the speed of light. Such transient electromagnetic fields may induce various novel effects in the hydrodynamic description of the quark gluon plasma for non-central heavy-ion collisions. We investigate the longitudinal acceleration effects on the 1+1 dimensional relativistic magnetohydrodynamics with transverse magnetic fields. We analyze the proper time evolution of the system energy density. We find that the longitudinal acceleration parameter $λ^*$, magnetic field decay parameter $a$, equation of state $κ$, and initial magnetization $σ_0$ have nontrivial effects on the evolutions of the system energy density and temperature.

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arXiv2018

The QED Radiative Corrections to Chiral Magnetic Effect

We study in this paper the radiative corrections to chiral magnetic current at both zero and nonzero temperature. Our motivation is a radiative correction to the matrix element of the anomalous Ward identity in massless QED stemming from a three-loop diagram where the two photons coming from the one-loop anomalous triangle are re-scattered. Through the interplay between the Ward identity and the infrared subtlety of the fermion loop integral, we are able to reproduce the corrections known in literature in a simpler approach and obtain its contribution to the chiral magnetic current at zero temperature. At a nonzero temperature, the infrared subtlety disappeared in a static magnetic field and the three-loop diagram does not contribute to the chiral magnetic current any more. The generalization to all orders of the massless QED and the QCD corrections are discussed.

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arXiv2018

Fluctuation and Dissipation of Axial Charge from Massive Quarks

In quantum chromodynamics (QCD), axial charge is known to be non-conserved due to chiral anomaly and non-vanishing quark mass. In this paper, we explore the role of quark mass in axial charge fluctuation and dissipation. We present two separate calculations of axial charge correlator, which describe dynamics of axial charge. The first is free quarks at finite temperature. We find that axial charge can be generated through effective quantum fluctuations in free theory. However the fluctuation does not follow a random walk behavior. Due to the presence of axial symmetry breaking mass term, the axial charge also does not settle asymptotically to the thermodynamic limit given by susceptibility. The second calculation is in weakly coupled quark gluon plasma (QGP). We find in the hard thermal loop (HTL) approximation, the quark-gluon interaction leads to random walk growth of axial charge, but dissipation is not visible. We estimate relaxation time scale for axial charge, finding it lies beyond the HTL regime.

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arXiv2018

Drag force in a D-instanton background

We study the drag force and diffusion coefficient with respect to a moving heavy quark in a D-instanton background, which corresponds to the Yang-Mills theory in the deconfining, high-temperature phase. It is shown that the presence of the D-instanton density tends to increase the drag force and decrease the diffusion coefficient, reverse to the effects of the velocity and the temperature. Moreover, the inclusion of the D-instanton density makes the medium less viscous.

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arXiv2018

Higher derivative corrections to the entropic force from holography

The entropic force has been recently argued to be responsible for dissociation of heavy quarkonia. In this paper, we analyze $R^2$ corrections and $R^4$ corrections to the entropic force, respectively. It is shown that for $R^2$ corrections, increasing $λ_{GB}$ (Gauss-Bonnet factor) leads to increasing the entropic force. While for $R^4$ corrections, increasing $λ$ ('t Hooft coupling) leads to decreasing the entropic force. Also, we discuss how the entropic force changes with the shear viscosity to entropy density ratio, $η/s$, at strong coupling.

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arXiv2018

Drag force in strongly coupled $\mathcal{N}=4$ SYM plasma in a magnetic field

Applying AdS/CFT correspondence, we study the effect of a constant magnetic field $\mathcal{B}$ on the drag force associated with a heavy quark moving through a strongly-coupled $\mathcal{N}=4$ supersymmetric Yang-Mills (SYM) plasma. The quark is considered moving transverse and parallel to $\mathcal{B}$, respectively. It is shown that for transverse case, the drag force is linearly dependent on $\mathcal{B}$ in all regions. While for parallel case, the drag force increases monotonously with increasing $\mathcal{B}$ and also reveals a linear behavior in the regions of strong $\mathcal{B}$. In addition, we find that $\mathcal{B}$ has important effect for transverse case than parallel.

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arXiv2018

Imaginary potential in strongly coupled $\mathcal{N}=4$ SYM plasma in a magnetic field

We study the effect of a constant magnetic field on the imaginary part of a quarkonia potential in a strongly-coupled $\mathcal{N}=4$ SYM plasma. We consider the pair axis to be aligned perpendicularly and parallel to the magnetic field, respectively. For both cases, we find that the presence of the magnetic field tends to enhance the imaginary potential thus decreasing the the thermal width. In addition, the magnetic field has a stronger effect on the imaginary potential when the pair axis is perpendicular to the magnetic field rather than parallel.

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arXiv2017

Imaginary potential of moving quarkonia in a D-instanton background

The imaginary part of the inter-quarks potential of moving heavy quarkonia is investigated in a dual supergravity of the AdS background deformed by dilaton, which induces the gauge field condensate in the dual gauge theory. We analyze the quark anti-quark pair moving transverse and parallel to the plasma wind, respectively. It is shown that for both cases the presence of D-instanton density tends to increase the inter-distance and decrease the imaginary potential, reverse to the effect of the pair's velocity. Moreover, it is found that the D-instanton density has stronger effects for the parallel case rather than transverse.

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arXiv2017

The HTL resumed propagators in the light cone gauge

The expression of the HTL resumed gluon propagator in the light cone gauge is derived. In the real time mechanism, using the Mandelstam Leibbrant prescription of $(n\cdot K)^{-1}$, we calculate the transverse and longitudinal parts of the gluon HTL self-energy and prove the transverse and longitudinal parts do not have divergence. We also calculate the quark self energy in the HTL approximation, and find it gauge independent. We analytically calculate the damping rates of the hard quark and gluon with this HTL resumed gluon propagator.

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arXiv2017

$R^2$ corrections to holographic Schwinger effect

We study $R^2$ corrections to the holographic Schwinger effect in an AdS black hole background and a confining D3-brane background, respectively. The potential analysis for these backgrounds is presented. The critical values for the electric field are obtained. It is shown that for both backgrounds increasing the Gauss-Bonnet parameter the Schwinger effect is enhanced. Moreover, the results provide an estimate of how the Schwinger effect changes with the shear viscosity to entropy density ratio, $η/s$, at strong coupling.

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