arXiv subjects

M. Ali-Akbari

Publications and source records attributed to M. Ali-Akbari.

At least 19 recordsLinked to original sources

arXiv2026

Velocity dependence of holographic entanglement entropy in a charged plasma

We have studied holographic entanglement entropy in a moving thermal gauge theory with a non-zero chemical potential. A sufficiently high velocity enhances the holographic entanglement entropy, particularly for larger values of the chemical potential. However, at high temperature and velocity, the chemical potential dependence is almost entirely washed out, indicating that thermal fluctuations dominate over charge-density effects. In the ultrarelativistic regime, the holographic entanglement entropy grows very rapidly with velocity, which emerges as the dominant parameter, largely suppressing both thermal and chemical contributions.

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arXiv2026

HTEE vs. Pseudo-Entropy in Magnetic Fields

We compare the holographic timelike entanglement entropy with the pseudo-entropy arising from a two-qubit quantum mechanical system. In this model, we consider transitions from an initial thermal state to a final thermal state at fixed temperature under the influence of an external magnetic field. Our findings highlight significant discrepancies between the two quantities, which display markedly different behavior.

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arXiv2026

On Holographic Time-Like Entanglement Entropy

In this paper, we compare and analyze holographic timelike entanglement entropy with pseudo-entropy in quantum mechanics for a two-qubit system, considering transitions from a thermal state to an anisotropic thermal state at fixed temperature. We identify several common properties but also report important differences between these quantities.

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arXiv2022

Non-Conformal Behavior of Holographic Entanglement Measures

We evaluate the holographic entanglement entropy, HEE, holographic mutual information, HMI, and holographic entanglement of purification, EoP, in a non-conformal model at zero and finite temperature. In order to find the analytical results we consider some specific regimes of the parameter space. We find that the non-conformal effects decrease the redefined HEE and increase the redefined HMI and EoP in the all studied regimes. On the other side, the temperature effects increase (decrease) the redefined HEE (HMI) in the all studied regimes while it has no definite effect on the redefined EoP. Finally, from the information point of view, we find that in the vicinity of the phase transition the zero temperature state is more favorable than the finite temperature one.

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arXiv2021

Non-Conformality, Subregion Complexity and Meson Binding

We study holographically the zero and finite temperature behavior of the potential energy and holographic subregion complexity corresponding to a probe meson in a non-conformal model. We observe that in zero and low temperature non-conformality has a decreasing effect on the dimensionless meson potential energy. However, non-conformal corrections increase absolute value of the dimensionless holographic subregion complexity in both zero and finite temperature which means the non-conformal state needs less information to be specified. In other words, considering the effect of non-conformality, the less bounded meson state needs less information to be specified. In low temperature limits, thermal corrections decrease meson potential energy and do not have a specific effect on holographic subregion complexity. We find that in the vicinity of the phase transition, the zero temperature meson state is more favorable than the finite temperature state, from the holographic subregion complexity point of view.

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arXiv2021

Temperature Dependence of Entanglement of Purification in Presence of Chemical Potential

Using holographic idea, we study the entanglement of purification in a field theory with a critical point in intermediate and low temperature regime. This theory includes temperature $T$ as well as chemical potential $μ$. In the intermediate regime, due to chemical potential, we observe that new terms proportional to temperature square appear in the final result of entanglement of purification or equivalently, apart from $T^0$ and $T^4$ terms in the case of $μ=0$, it contains the terms proportional to $T^2$. Our results also indicate that the entanglement of purification, i.e. the correlation between subsystems, can decrease or increase depending on the value of $\fracμ{T}$ when the other parameters are kept fixed. However, in the low temperature limit, the correlation always decreases, comparing to the $μ=0$ case, independent of the value of $\fracμ{T}$ when the other parameters do not alter. The existence of a critical point in the theory changes the behavior of entanglement of purification in such a way that the entanglement of purification experiences a maximum or minimum. Moreover, near the critical point, we analytically show that the critical exponent is equal to 0.5 in both regimes and also the term proportional to $T^2$ changes sign and becomes negative in the intermediate regime.

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arXiv2020

Holographic Entanglement of Purification near a Critical Point

In the presence of finite chemical potential $μ$, we holographically compute the entanglement of purification in a $2+1$- and $3+1$-dimensional field theory and also in a $3+1$-dimensional field theory with a critical point. We observe that compared to $2+1$- and $3+1$-dimensional field theories, the behavior of entanglement of purification near critical point is different and it is not a monotonic function of $\fracμ{T}$ where $T$ is the temperature of the field theory. Therefore, the entanglement of purification distinguishes the critical point in the field theory. We also discuss the dependence of the holographic entanglement of purification on the various parameters of the theories. Moreover, the critical exponent is calculated.

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arXiv2020

Holographic Mutual and Tripartite Information in a Non-Conformal Background

Holographic mutual and tripartite information have been studied in a non-conformal background. We have investigated how these observables behave as the energy scale and number of degrees of freedom vary. We have found out that the effect of degrees of freedom and energy scale is opposite. Moreover, it has been observed that the disentangling transition occurs at large distance between sub-systems in non-conformal field theory independent of l. The mutual information in a non-conformal background remains also monogamous.

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arXiv2019

Evolution of Holographic Complexity Near Critical Point

The holographic complexity has been studied in a background which includes a critical point in the dual field theory. We have examined how the complexity rate and the saturation time of dynamical variables in the theory behave as one moves towards the critical point. Two significant results of our analysis are that (i) it takes more time for the complexity in field theory dual to become time dependent as one moves away from the critical point and (ii) near the critical point the complexity starts evolving linearly in time sooner than the other points away from it. We also observe different behaviour for complexity rate in action and volume prescriptions. In action prescription we have used the time scales in theory to obtain the dynamical critical exponent and interestingly have observed that different time scales produce the same value up to very small error.

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arXiv2018

Holographic Mutual and Tripartite Information in a Symmetry Breaking Quench

We study the time evolution of holographic mutual and tripartite information for a zero temperature $CFT$, derives to a non-relativistic thermal Lifshitz field theory by a quantum quench. We observe that the symmetry breaking does not play any role in the phase space, phase of parameters of sub-systems, and the length of disentangling transition. Nevertheless, mutual and tripartite information indeed depend on the rate of symmetry breaking. We also find that for large enough values of $δt$ the quantity $t_{eq}δt^{-1}$, where $δt$ and $t_{eq}$ are injection time and equilibration time respectively, behaves universally, $i.e.$ its value is independent of length of separation between sub-systems. We also show that tripartite information is always non-positive during the process indicates that mutual information is monogamous.

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arXiv2018

Holographic Entanglement Entropy Decomposition in an Anisotropic Gauge Theory

We study holographic entanglement entropy in spatially anisotropic field theory. We observe that for the background we consider in this paper, to a good approximation, the holographic entanglement entropy can be decomposed into two terms. One of them is the entanglement entropy of the isotropic field theory at fixed temperature and the other term is only a function of anisotropy parameter. Moreover, for large enough values of anisotropy parameter, our numerical results indicate that the entanglement entropy in the perpendicular direction to anisotropic direction is greater than the parallel case.

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arXiv2017

Far-from-equilibrium initial conditions probed by a nonlocal observable

Using the gauge/gravity duality, we investigate the evolution of an out-of-equilibrium strongly-coupled plasma from the viewpoint of the two-point function of scalar gauge-invariant operators with large conformal dimension. This system is out of equilibrium due to the presence of anisotropy and/or a massive scalar field. Considering various functions for the initial anisotropy and scalar field, we conclude that the effect of the anisotropy on the evolution of the two-point function is considerably more than the effect of the scalar field. We also show that the ordering of the equilibration time of the one-point function for the non-probe scalar field and the correlation function between two points with a fixed separation can be reversed by changing the initial configuration of the plasma, when the system is out of the equilibrium due to the presence of at least two different sources like our problem. In addition, we find the equilibration time of the two-point function to be linearly increasing with respect to the separation of the two points with a fixed slope, regardless of the initial configuration that we start with. Finally we observe that, for larger separations the geodesic connecting two points on the boundary crosses the event horizon after it has reached its final equilibrium value, meaning that the two-point function can probe behind the event horizon.

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arXiv2017

AdS/QCD, Entanglement Entropy and Critical Temperature

Based on gauge-gravity duality, by using holographic entanglement entropy, we have done a phenomenological study to probe confinement-deconfinement phase transition in the QCD-like gauge theory. Our outcomes are in perfect agreement with the expected results, qualitatively and quantitatively. We find out that the (holographic) entanglement entropy is a reliable order parameter for probing the phase transition.

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arXiv2017

Entanglement Entropy in a Non-Conformal Background

We use gauge-gravity duality to compute entanglement entropy in a non-conformal background with an energy scale $Λ$. At zero temperature, we observe that entanglement entropy decreases by raising $Λ$. However, at finite temperature, we realize that both $\fracΛ{T}$ and entanglement entropy rise together. Comparing entanglement entropy of the non-conformal theory, $S_{A(N)}$, and of its conformal theory at the $UV$ limit, $ S_{A(C)}$, reveals that $S_{A(N)}$ can be larger or smaller than $S_{A(C)}$, depending on the value of $\fracΛ{T}$.

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arXiv2017

A Classical String in Lifshitz-Vaidya Geometry

We study the time evolution of the expectation value of a rectangular Wilson loop in strongly anisotropic time-dependent plasma using gauge-gravity duality. The corresponding gravity theory is given by describing time evolution of a classical string in the Lifshitz-Vaidya background. We show that the expectation value of the Wilson loop oscillates about the value of the static potential with the same parameters after the energy injection is over. We discuss how the amplitude and frequency of the oscillation depend on the parameters of the theory. In particular, by raising the anisotropy parameter, we observe that the amplitude and frequency of the oscillation increase.

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arXiv2016

Holographic Equilibration under External Dynamical Electric Field

The holographic equilibration of a far-from-equilibrium strongly coupled gauge theory is investigated. The dynamics of a probe D7-brane in an AdS-Vaidya background is studied in the presence of an external time-dependent electric field. Defining the equilibration times $t_{eq}^c$ and $t_{eq}^j$, at which condensation and current relax to their final equilibrated values, receptively, the smallness of transition time $k_M$ or $k_E$ is enough to observe a universal behaviour for re-scaled equilibration times $k_M k_E (t_{eq}^c)^{-2}$ and $k_M k_E (t_{eq}^j)^{-2}$. Moreover, regardless of the values for $k_M$ and $k_E$, $t_{eq}^c/t_{eq}^j$ also behaves universally for large enough value of the ratio of the final electric field to final temperature. Then a simple discussion of the static case reveals that $t_{eq}^c \leq t_{eq}^j$. For an out-of-equilibrium process, our numerical results show that, apart from the cases for which $k_E$ is small, the static time ordering persists.

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arXiv2016

Time-Dependent Meson Melting in External Magnetic Field

The dynamics of a probe D7-brane in an asymptotically AdS-Vaidya background has been investigated in the presence of an external magnetic field. Holographically, this is dual to the dynamical meson melting in the N = 2 super Yang-Milles theory. If the final temperature of the system is large enough, the probe D7-brane will dynamically cross the horizon (black hole embedding). By turning on the external magnetic field and raising it sufficiently, the final embedding of the corresponding D7-brane changes to Minkowski embedding. In the field theory side, this means that the mesons which melt due to the raise in the temperature, will form bound states again by applying an external magnetic field. We will also show that the evolution of the system to its final equilibrium state is postponed due to the presence of the magnetic field.

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arXiv2016

Various Time-Scales of Relaxation

Via gauge-gravity duality, relaxation of far-from-equilibrium initial states in a strongly coupled gauge theory has been investigated. In the system we consider in this paper there are two ways where the state under study can deviate from its equilibrium: anisotropic pressure and time-dependent expectation value of a scalar operator with Δ=3. In the gravity theory, this system corresponds to Einstein's general relativity with a non-trivial metric, including the anisotropy function, coupled to a massive scalar matter field. We study the effect of different initial configurations for scalar field and anisotropy function on physical processes such as thermalization, i.e. time evolution of event horizon, equilibration of the expectation value of scalar operator and isotropization. We also discuss time ordering of these time-scales.

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