arXiv subjects

Zi-qiang Zhang

Publications and source records attributed to Zi-qiang Zhang.

At least 19 recordsLinked to original sources

arXiv2026

Holographic Schwinger effect with Translational Symmetry Breaking

We investigate the holographic Schwinger effect in a background with translational symmetry breaking (TSB) at finite chemical potential. The gravitational background is characterized by two independent parameters: the TSB parameter $α$, which controls momentum relaxation, and the chemical potential $μ$, which determines the finite density of the dual field theory. Using the potential analysis method, we derive the total potential governing the pair production process and examine its dependence on $α$, $μ$, the external magnetic field, and the ratio $β=E/E_c$. Our results show that the effects of $α$ and $μ$ on the Schwinger process strongly depend on the dynamical regime. In the subcritical regime, increasing either $α$ or $μ$ lowers the potential barrier and facilitates pair production. However, near and above the critical electric field, the roles of these two parameters become qualitatively different. While increasing the chemical potential lowers the total potential and enhances the Schwinger pair production process, increasing the translational symmetry breaking parameter shifts the potential upward and suppresses the production process. We further show that, at fixed $β=E/E_c$, a perpendicular external magnetic field lowers the effective potential barrier and thereby facilitates the Schwinger process, while the physical electric field changes accordingly through the magnetic-field dependence of $E_c$. The corresponding pair production rate is not independently calculated; instead, its qualitative behavior is characterized through a proxy derived from the total potential. Overall, our analysis provides a comprehensive picture of how translational symmetry breaking, finite density, and external magnetic fields influence holographic non-perturbative pair production.

hep-th↗

arXiv2026

Spin alignment of vector mesons in a plasma at finite density

We study the spectral functions and spin alignment of $J/ψ$ and $ϕ$ mesons at finite density in a soft-wall holographic model. The quark-gluon plasma background is described by a charged black hole geometry, and the vector mesons are treated as probe bulk vector fields. The present analysis extends the zero-density study of Phys. Rev. D 110 (2024) 056047 (Ref.~\cite{XLS2024}) to finite density; in the zero-density limit our results reproduce the corresponding findings. We derive the relation between the production rates in different spin channels and the corresponding in-medium spectral functions, and examine their dependence on the chemical potential, meson momentum, and temperature. We analyze the spin alignment induced by the motion of the vector meson relative to the thermal bath. At $T=0.15~\mathrm{GeV}$, the $J/ψ$ spectral function exhibits a clear resonance peak, indicating that the $c\bar{c}$ pair can still form a quasistable bound state. As the chemical potential increases, this peak becomes lower and broader, signaling enhanced dissociation in the medium. For the $ϕ$ meson at the same temperature, no pronounced peak is observed, indicating substantial melting; its spectral function thus better characterizes the distribution of unstable $s\bar{s}$ pairs in the thermal environment. At $T=0.15~\mathrm{GeV}$, the helicity-frame spin alignment parameter $ρ_{00}$ shows a positive deviation from $1/3$ for the $J/ψ$ and a negative one for the $ϕ$ meson. A finite chemical potential alters these deviations, reducing the magnitude for the $J/ψ$ while increasing it for the $ϕ$ meson. The calculations are performed within a bottom-up soft-wall model; the results should be read as model-based estimates rather than model-independent predictions.

hep-ph↗

arXiv2026

Holographic light quark jet quenching in flavor resolved QCD plasmas

We investigate light quark energy loss in a quark-gluon plasma using the holographic falling string setup. Stopping distances are computed from null geodesics in an Einstein-Maxwell-dilaton (EMD) background whose thermodynamics are lattice calibrated for three compositions: pure glue, two flavor QCD, and full QCD with strangeness. This geometry mirrors that of recent shooting string simulations, enabling a direct comparison between integrated stopping lengths and differential energy loss. Systematic scans over temperature, baryon chemical potential, and path length reveal that near the QCD crossover, plasmas with more dynamical flavors exhibit stronger quenching, consistent with RHIC strange hadron suppression data. At higher temperatures, approaching the conformal regime, this flavor hierarchy reverses, a trend absent in flavorless models. Finite baryon chemical potential shortens stopping distances and enhances energy loss, with marked sensitivity near the QCD critical endpoint, mirroring anomalies observed in RHIC beam energy scans. Consistent trends from these two independent holographic observables rule out formalism specific artifacts and support the reliability of our lattice calibrated EMD framework. We further discuss the geometric origin of the high temperature flavor ordering, parameter sensitivities, and possible extensions to heavy ion transport simulations.

hep-ph↗

arXiv2026

Gluon condensate effects on heavy quarkonium spectral functions and thermal dissociation

We investigate how the gluon condensate modifies the thermal spectral functions and melting patterns of heavy vector mesons, specifically charmonium and bottomonium, using an improved soft-wall AdS/QCD model. The framework is extended to finite temperature via a dilaton black hole geometry that consistently incorporates the backreaction from the gluon condensate. We numerically track the evolution of spectral resonance peaks as functions of both temperature and gluon condensate strength. Our calculations reveal that increasing temperature systematically broadens and suppresses spectral peaks, signaling in-medium dissociation. In contrast, a stronger gluon condensate considerably mitigates peak broadening and enhances the spectral weight of both ground and excited states. This behavior indicates that the gluon condensate hinders thermal dissociation, thereby stabilizing heavy quarkonia within the quark-gluon plasma. These findings are consistent with existing studies and provide new holographic evidence for the stabilising role of the gluon condensate from the perspective of thermal spectral functions.

hep-ph↗

arXiv2026

Holographic study of heavy quark potential, free energy, and running coupling in backgrounds with broken translational symmetry

We study heavy-quark observables including static interquark potential, thermal free energy and running coupling via a five-dimensional asymptotically AdS spacetime with translational symmetry breaking (TSB). The Einstein-Maxwell-axion geometry involves two scales: chemical potential $μ$ for finite baryon density, and TSB parameter $β$ for momentum relaxation. Numerical simulations at finite and zero temperature reveal that both $μ$ and $β$ weaken color interactions and facilitate quarkonium dissociation in strongly coupled quark-gluon plasmas through different mechanisms. The chemical potential dominates color screening and modifies the heavy-quark potential and running coupling, while $β$ mainly affects plasma entropy and corrects thermal free energy. At zero temperature, thermal contributions vanish, and the renormalized free energy becomes a medium-modified static potential with an approximate Coulombic form. Finite baryon density suppresses $Q\bar{Q}$ binding much more strongly than momentum dissipation at all temperatures. We extract the color screening length and dissociation scale, and discuss phenomenological implications for quarkonium in heavy-ion collisions. This work clarifies medium correction mechanisms for color interactions and thermodynamics, and presents a consistent picture for heavy-quark probes in dense dissipative plasmas.

hep-th↗

arXiv2023

Holographic Schwinger effect in spinning black hole backgrounds

We perform the potential analysis for the holographic Schwinger effect in spinning Myers-Perry black holes. We compute the potential between the produced pair by evaluating the classical action of a string attaching on a probe D3-brane sitting at an intermediate position in the AdS bulk. It turns out that increasing the angular momentum reduces the potential barrier thus enhancing the Schwinger effect, consistent with previous findings obtained from the local Lorentz transformation. In particular, these effects are more visible for the particle pair lying in the transversal plane compared with that along the longitudinal orientation. In addition, we discuss how the Schwinger effect changes with the shear viscosity to entropy density ratio at strong coupling under the influence of angular momentum.

hep-ph↗

arXiv2023

Holographic imaginary potential of a quark antiquark pair in the presence of gluon condensation

For a moving heavy quark antiquark ($Q\bar{Q}$) in a quark gluon plasma (QGP), we use gauge/gravity duality to study both real and imaginary parts of the potential (Re$V_{Q\bar{Q}}$ and Im$V_{Q\bar{Q}}$ respectively) in a gluon condensate (GC) theory. The complex potential is derived from the Wilson loop by considering the thermal fluctuations of the worldsheet of the Nambu-Goto holographic string. We calculate Re$V_{Q\bar{Q}}$ and Im$V_{Q\bar{Q}}$ in both cases where the axis of the moving $Q\bar{Q}$ pair is transverse and parallel with respect to its direction of movement in the plasma. Using the renormalization scheme for the Re$V_{Q\bar{Q}}$ , we find that the inclusion of GC increases the dissociation length while rapidity has the opposite effect. While for the Im$V_{Q\bar{Q}}$ , we observe that by considering the effect of GC, the Im$V_{Q\bar{Q}}$ is generated for larger distance thus decreasing quarkonium dissociation, while rapidity has opposite effect. In particular, as the value of GC decreases in the deconfined phase, the Im$V_{Q\bar{Q}}$ is generated for smaller distance thus enhancing quarkonium dissociation, and at high temperatures it is nearly not modified by GC, consistent with previous findings of the entropic force.

hep-ph↗

arXiv2022

Entropic destruction of heavy quarkonium in a rotating hot and dense medium from holography

Previous studies have indicated that the peak of the quarkonium entropy at the deconfinement transition can be related to the entropic force which would induce the dissociation of heavy quarkonium. In this paper, we study the entropic force in a rotating hot and dense medium using AdS/CFT correspondence. It turns out that the inclusion of angular velocity increases the entropic force thus enhancing quarkonium dissociation, while chemical potential has the same effect. Furthermore, the results imply that the quarkonium dissociates easier in rotating medium compared to static case.

nucl-th↗

arXiv2022

Holographic Schwinger effect in a rotating strongly coupled medium

We perform the potential analysis for the holographic Schwinger effect in a rotating deformed AdS black-hole background. We calculate the total potential of a quark-antiquark ($Q\bar{Q}$) pair in an external electric field and evaluate the critical electric field from Dirac-Born-Infeld (DBI) action. It is shown that the inclusion of angular velocity decreases the potential barrier thus enhancing the Schwinger effect, opposite to the effect of the confining scale. Moreover, by increasing angular velocity decreases the critical electric field above which the pairs are produced freely without any suppression. Furthermore, we conclude that producing $Q\bar{Q}$ pairs would be easier in rotating medium.

hep-th↗

arXiv2021

Entropic destruction of heavy quarkonium with hyperscaling violation

We study the entropic destruction of heavy quarkonium in strongly coupled theories with an anisotropic scaling symmetry in time and spatial direction. We consider Lifshitz and hyperscaling violation theories which are covariant under a generalized Lifshitz scaling symmetry with the dynamical exponent $z$ and hyperscaling violation exponent $θ$. It is shown that the entropic force depends on the parameters of these theories. In particular, increasing $z$ decreases the entropic force thus reducing the quarkonium dissociation, while increasing $θ$ has opposite effect.

hep-ph↗

arXiv2020

Light quark energy loss in a soft-wall AdS/QCD model

We investigate the energy loss of light quarks in a holographic QCD model with conformal invariance broken by a background dilaton. We perform the analysis within falling string and shooting string, respectively. It turns out that the two methods give the same result: the presence of chemical potential and confining scale tends to enhance the energy loss, in accord with previous findings of drag force and jet quenching parameter.

nucl-th↗

arXiv2020

Holographic Schwinger effect in a soft wall AdS/QCD model

We perform the potential analysis for the holographic Schwinger effect in a deformed $AdS_5$ model with conformal invariance broken by a background dilaton. We evaluate the static potential by analyzing the classical action of a string attaching the rectangular Wilson loop on a probe D3 brane sitting at an intermediate position in the bulk AdS space. We observe that the inclusion of chemical potential tends to enhance the production rate, reverse to the effect of confining scale. Also, we calculate the critical electric field by Dirac-Born-Infeld (DBI) action.

hep-th↗

arXiv2020

Jet quenching parameter from a soft wall AdS/QCD model

We study the effect of chemical potential and nonconformality on the jet quenching parameter in a holographic QCD model with conformal invariance broken by a background dilaton. It turns out that the presence of chemical potential and nonconformality both increase the jet quenching parameter thus enhancing the energy loss, consistently with the findings of the drag force.

nucl-th↗

arXiv2020

Entropic destruction of heavy quarkonium in heavy quark cloud

Previous research has shown that the peak of the quarkonium entropy at the deconfinement transition would be related to the entropic force which induces the melting of quarkonium. In this article, we study the effect of backreaction on the entropic force in a strongly coupled plasma of adjoint matter. The backreaction covered here comes from the presence of static heavy quarks evenly distributed over such a plasma. It is found that the inclusion of backreaction increases the entropic force thus enhancing the quarkonium dissociation, in accord with the findings of the imaginary potential.

hep-th↗

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.

hep-th↗

arXiv2018

$R^4$ corrections to holographic Schwinger effect

We consider $R^4$ corrections to the holographic Schwinger effect in an AdS black hole background and a confining D3-brane background. The potential between a test particle pair are performed for both backgrounds. We find there is no potential barrier in the critical electric field, which means that the system becomes catastrophically unstable. It is shown that for both backgrounds increasing the inverse 't Hooft coupling parameter $1/λ$ enhances the Schwinger effect. We also discuss the possible relation between the Schwinger effect and the viscosity-entropy ratio $η/s$ in strong coupling.

hep-th↗

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.

hep-th↗

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.

hep-th↗