arXiv subjects

Shahrokh Parvizi

Publications and source records attributed to Shahrokh Parvizi.

At least 19 recordsLinked to original sources

arXiv2025

Generalized volume-complexity for Lovelock black holes

We study the time dependence of the generalized complexity of Lovelock black holes using the ``complexity = anything" conjecture, which expands upon the notion of ``complexity = volume" and generates a large class of observables. By applying a specific condition, a more limited class can be chosen, whose time growth is equivalent to a conserved momentum. Specifically, we investigate the numerical full time behavior of complexity time rate, focusing on the second and third orders of Lovelock theory coupled with Maxwell term, incorporating an additional term -- the square of the Weyl tensor of the background spacetime -- into the generalization function. Furthermore, we repeat the analysis for case with three additional scalar terms: the square of Riemann and Ricci tensors, and the Ricci scalar for second-order gravity (Gauss-Bonnet) showing how these terms can affect to multiple asymptotic behavior of time. We study how the phase transition of generalized complexity and its time evolution occur at turning point $(τ_{turning})$ where the maximal generalized volume supersedes another branch. Additionally, we discuss the late time behavior, focusing on proportionality of the complexity time rate to the difference of temperature times entropy at the two horizons ($TS(r_+)-TS(r_-)$) for charged black holes, which can be corrected by generalization function of each radius in generalized case. In this limit, we also explore near singularity structure by approximating spacetime to Kasner metrics and finding possible values of complexity growth rate with different choices of the generalization function.

hep-th↗

arXiv2024

Computational Complexity in Analogue Gravity

Analogue gravity helps to find some gravitational systems which are similar to the evolution of perturbation in condensed matter systems. These analogies provide a very good tool for either side. In other words, some aspects of gravity could be simulated in condensed matter laboratories. In this study, we are going to find an interpretation for computational complexity in condensed matter systems and the analogue of the uncertainty principle as the Lloyd bound. We show that this inequality roughly is equivalent to the KSS bound in the fluid/gravity duality and provides some experimental criteria to test the Lloyd bound in the laboratory.

hep-th↗

arXiv2023

Analogue gravity and the island prescription

Analogue gravity succeeded to simulate Hawking radiation and test it in laboratories. In this setting, the black hole is simulated by an area in a fluid, say water, where no sound wave can escape the event horizon and phonon oscillations are detected as Hawking radiation. This means that the analogue simulations can provide an alternative description, and consequently, a new insight to the high energy physics problems. Now it would be interesting to see what information loss means and how island prescription is interpreted in water experiment. In this paper we show that the analogue of information loss is the loss of momentum per unit mass of the fluid over the horizon and maintaining the momentum loss leads to the island prescription.

hep-th↗

arXiv2022

Curved Corner Contribution to the Entanglement Entropy in an Anisotropic Spacetime

In this article, we explore the divergences and universal terms of the holographic entanglement entropy for singular regions in anisotropic and nonconformal theories that are holographically dual to geometries with a hyperscaling violation, parameterized by two parameters $z$ and $θ$. We study a curved corner in anisotropic space with arbitrary $θ$ and $z$. We choose the region to be shape invariant under the scaling of spacetime. For this case, we show that the contribution of the singularity to the entanglement entropy depends on $z$ and $θ$ values. We identify the structure of various divergences that may appear, especially those which give rise to a universal contribution in the form of logarithmic or double logarithmic terms. In the range $z>1$, for values $z=2k/(2k-1)$ with some integer $k$ and $θ=0$, Lifshitz geometry, we find a double logarithmic term. In the range $z<0$, for values $θ=1-2n|z-1|$ with some integer $n$ we find a logarithmic term.

hep-th↗

arXiv2022

Constraints on anisotropic RG flows from holographic entanglement entropy

In the context of the gauge/gravity duality, using the proposed candidate $c$-function, which is derived from the entanglement entropy of a strip-shaped region, we investigate the RG flow for $d+1$-dimensional quantum field theories with broken Lorentz and rotational symmetries in the IR, but preserved conformal invariance in the UV boundary. We examine conditions of monotonicity of the $c$-function for holographic anisotropic theories dual to the Einstein gravity via the constraints imposed by the null energy conditions. We consider near UV and IR behaviors and identify the sufficient conditions that guarantee the $c$ function decreases monotonically along the RG flows.

hep-th↗

arXiv2022

On Maximum Complexity in Holography

In a quantum circuit, it is believed that complexity itself reaches a maximum of order exponential in the number of q-bits or equivalently exponential in entropy of the black hole. However, the current holographic proposals do not meet this criterion. The holographic proposals find the complexity of the very late times to be linear in the entropy, while in the quantum circuit, it is expected that complexity meets within a finite time its maximum value in an exponential in the entropy. These points are required to be altered in holographic proposals of complexity. This paper introduces a new holographic proposal that meets this criterion and consolidates the Lloyd bound.

hep-th↗

arXiv2021

Circuit Complexity in $U(1)$ Gauge Theory

We study circuit complexity for a free vector field of a $U(1)$ gauge theory in Coulomb gauge, and Gaussian states. We introduce a quantum circuit model with Gaussian states, including reference and target states. Using the Nielsen's geometric approach, the complexity then can be found as the shortest geodesic in the space of states. This geodesic is based on the notion of geodesic distance on the Lie group of Bogoliubov transformations equipped with a right-invariant metric. We use the framework of the covariance matrix to compute circuit complexity between Gaussian states. We apply this framework to the free vector field in general dimensions where we compute the circuit complexity of the ground state of the Hamiltonian.

hep-th↗

arXiv2019

Relevant perturbation of entanglement entropy of singular surfaces

We study the entanglement entropy of theories that are derived from relevant perturbation of given CFTs for regions with a singular boundary by using the AdS/CFT correspondence. In the smooth case, it is well known that a relevant deformation of the boundary theory by the relevant operator with scaling dimension $Δ=\frac{d+2}{2}$ generates a logarithmic universal term to the entanglement entropy. As the smooth case, when the boundary CFT deformed by a relevant operator, we find that the entanglement entropy of singular surface also contains a new logarithmic term which is due to relevant perturbation of the conformal field theory, and depends on the scaling dimension of relevant operator. We also find for extended singular surfaces, $c_{n}\times R^{m}$, as well as logarithmic term, the new universal double logarithmic terms may appear depending on the scaling dimension of relevant operator and spacetime dimensions. These new terms are due to relevant perturbation of the boundary theory.

hep-th↗

arXiv2019

Holographic Aspects of a Higher Curvature Massive Gravity

We study the holographic dual of a massive gravity with Gauss-Bonnet and cubic quasi-topological higher curvature terms. Firstly, we find the energy-momentum two-point function of the 4-dimensional boundary theory where the massive term breaks the conformal symmetry as expected. An $a$-theorem is introduced based on the null energy condition. Then we focus on a black brane solution in this background and derive the ratio of shear viscosity to entropy density for the dual theory. It is worth mentioning that the concept of viscosity as a transport coefficient is obscure in a nontranslational invariant theory as in our case. So although we use the Green-Kubo's formula to derive it, we rather call it the rate of entropy production per the Planckian time due to a strain. Results smoothly cover the massless limit.

hep-th↗

arXiv2018

Entanglement entropy of singular surfaces under relevant deformations in holography

In the vacuum state of a CFT, the entanglement entropy of singular surfaces contains a logarithmic universal term which is only due to the singularity of the entangling surface. We consider the relevant perturbation of a three dimensional CFT for singular entangling surface. We observe that in addition to the universal term due to the entangling surface, there is a new logarithmic term which corresponds to a relevant perturbation of the conformal field theory with a coefficient depending on the scaling dimension of the relevant operator. We also find a new power law divergence in the holographic entanglement entropy. In addition, we study the effect of a relevant perturbation in the Gauss-Bonnet gravity for a singular entangling surface. Again a logarithmic term shows up. This new term is proportional to both the dimension of the relevant operator and the Gauss-Bonnet coupling. We also introduce the renormalized entanglement entropy for a kink region which in the UV limit reduces to a universal positive finite term.

hep-th↗

arXiv2017

Effect of massive potentials on the holographic thermalization

We perform a numerical study to recognize the difference between various massive potentials in the dRGT massive gravity on the holographic thermalization in the AdS and AdS Gauss-Bonnet gravities. The massive potential in $4+1$ dimensions includes three symmetric polynomial terms which we denote them as $a_1$, $a_2$ and $a_3$ terms. We observe, in the case of time evolution of entanglement entropy that there is a critical size of the entangling surface on the boundary below which both signs of $a_1$ and above the critical size $a_3$ are able to reduce the thermal value of entanglement entropy. Our numerical computations show the more positive $a_i$'s are, the faster system reaches to its thermal value. The order of saturation time of positive potentials when supplemented to AdS or AdS-GB backgrounds is as $t_{sat}(a_{1})>t_{sat}(a_{2})>t_{sat}(a_{3})$. We also explore these effects on the time evolution of the holographic mutual information.

hep-th↗

arXiv2015

The stability and gravitational Newtonian limit of a modified Randall-Sundrum model

For a modified Randall-Sundrum model [Phys. Rev. D 88 (2013) 025048], the graviton equations are derived and the mass spectrum found. The latter includes a massless graviton and a continuum mass with a gap. There is no negative mass-squared in the spectrum, so the model is stable. The gravitational Newtonian limit is obtained with an exponentially suppressed modification from extra dimension.

gr-qc↗

arXiv2015

Shear Viscosity to Entropy Density for a Black Brane in 5-dimensional Einstein-Yang-Mills Gravity

We calculate the ratio of shear viscosity to entropy density for a black brane of $5$-dimensional Einstein-Yang-Mills Gravity by Kubo and membrane paradigm methods. The former gives $\frac{1}{4π}$ exactly which is an expected result in the context of the Einstein-Hilbert gravity. In contrast, the membrane paradigm reaches $\frac{1}{4π}$ only in large horizon radius limit. We comment on this discrepancy.

hep-th↗

arXiv2015

Hydrodynamics of a Black Brane in Gauss-Bonnet Massive Gravity

A black brane solution to a Gauss-Bonnet massive gravity is introduced. In the context of AdS/CFT correspondence, the viscosity to entropy ratio is found by the Green-Kubo formula. The result indicates violation of the well-known KSS bound as expected in a higher derivative theory. Setting mass zero gives back the known viscosity to entropy ratio dependent on the Gauss-Bonnet coupling, while without Gauss-Bonnet term, a nonzero mass parameter doesn't contribute to the ratio which saturates the bound of $1/4π$.

hep-th↗

arXiv2014

Graviton Propagation in an Asymmetric Warped Background: Lorentz Violation and the Null Energy Condition

The graviton propagation in an asymmetric background is studied. The background is a configuration in the six-dimensional Salam-Sezgin model, in which a 3-form H-field turned on [JHEP 0910(2009)086]. The compact dimensions form a cylindrical space with branes as boundaries. The background gets asymmetry due to the H-field and violates the Lorentz symmetry. We derive the graviton equation in this background and show that it gets massless mode traveling with superluminal speed. A tower of K-K modes exists with a mass gap. On the other hand, it is known that breaking the Lorentz symmetry on an asymmetric background is constrained by the null energy condition. This no-go theorem doesn't work well in six-dimensional space-times and by this model we provide a counterexample for which the null energy condition is satisfied while the Lorentz symmetry is gravitationally violated.

hep-th↗

arXiv2013

dS Solutions with co-dimension two branes in six dimensions

We investigate 4D dS solutions with co-dimension two branes and finite 4D Planck mass in six dimensions. We present the conditions under which six-dimensional compactifications with holomorphic axion-dilaton field or models with pure gravity with local sources can yield 4D dS solutions. Different classes of solutions are specified by a holomorphic function describing different embeddings of multiple conical branes. Depending on the local singularities of this holomorphic function and the topology of the compact dimension one has to introduce D3-branes creating a deficit angle equal to πand/or D4-branes with positive tensions.

hep-th↗

arXiv2009

3-Form Flux Compactification of Salam-Sezgin Supergravity

The compactification of 6 dimensional Salam-Sezgin model in the presence of 3-form flux H is investigated. We find a torus topology for this compactification with two cusps which are the places of branes, while at the limit of large size L of the compact direction we also obtain sphere topology. This resembles the Randall-Sundrum I,II model. The branes at one of the cusps can be chosen to be 3- and 4-branes which fill our 4-dimensional space together with the fact that H=0 at this position restores the Lorentz symmetry. This compactification also provides an example for the so-called `time warp' solution, [0812.5107 [hep-th]]. According to a no-go theorem in $d\ne 6$, the time warp compactification violates the null energy condition. While the theorem is quiet for d=6, our model gives a time warp compactification which satisfies the null energy condition. We also derive the four dimensional effective Planck mass which is not obvious due to the time warp nature of the solution.

hep-th↗

arXiv2007

AdS/CFT correspondence via R-current correlation functions revisited

Motivated by realizing open/closed string duality in the work by Gopakumar [Phys. Rev. D70:025009,2004], we study two and three-point correlation functions of R-current vector fields in N=4 super Yang-Mills theory. These correlation functions in free field limit can be derived from the worldline formalism and written as heat kernel integrals in the position space. We show that reparametrizing these integrals converts them to the expected AdS supergravity results which are known in terms of bulk to boundary propagator. We expect that this reparametrization corresponds to transforming open string moduli parameterization to the closed string ones.

hep-th↗