Searcharxiv⌕ Search

arXiv subjects

Farzad Omidi

Publications and source records attributed to Farzad Omidi.

13 recordsLinked to original sources
arXiv2026

Entanglement Dynamics by (Non-)Unitary Local Operator Quenches in a 2D Holographic CFT

In this paper, we investigate the time evolution of entanglement entropy and mutual information for the spatially-infinite systems where we act with a primary operator on the vacuum state and then time-evolve it with the sequence of the Euclidean and Lorentzian time evolutions. Two-dimensional holographic conformal field theories describe the systems under consideration in this paper. The Euclidean time evolution is induced by the Rindler Hamiltonian and behaves as the regulator that tames the divergence induced by the local operator, while the Lorentzian one is induced by the uniform Hamiltonian. Under these time evolutions, we investigate the time ordering effect of the Rindler Euclidean and uniform Lorentzian time evolution operators. Consequently, we find the remarkable differences between those time evolutions are induced by whether those are unitary or non-unitary. Especially, we find that the unitary time evolution induces the late-time logarithmic growth of the entanglement entropy, while the non-unitary time evolution induces the late-time constant behavior. Furthermore, we investigate the dual gravity of the systems under consideration. Especially, we investigate the gravity duals of the systems with the insertion of the heavy primary operator and show that it is a black brane with a spacetime-dependent horizon.

hep-th↗
arXiv2025

Spacetime Bananas with EOW Branes and Spins

In this work, we study and generalize the spacetime banana proposal for computing correlation functions of huge operators in the context of the AdS$_3$/CFT$_2$ correspondence. First, we introduce time-like and space-like EOW branes into the proposal and demonstrate that: 1) a holographic dual of the one-point function in a BCFT can be obtained and its modified on-shell action reproduces the expected BCFT result; and 2) the GHY term on the stretched horizon can be replaced by the action of an EOW brane which wraps the horizon. Next, we discuss the two (one)-point function of huge spinning operators described by a rotating black hole in the bulk. We show that simply adding a GHY term on the stretched horizon is insufficient to reproduce the CFT results; instead, the appropriate modified action should be the micro-canonical action. Finally, we revisit the existing approaches for computing correlation functions using the gravity on-shell action of conical geometry or Ba$\tilde{\text{n}}$ados geometries. Surprisingly, we find that the on-shells actions of the Ba$\tilde{\text{n}}$ados geometries or the gravity solutions in the FG gauge yield unexpected incorrect results.

hep-th↗
arXiv2023

Pseudo Rényi Entanglement Entropies For an Excited State and Its Time Evolution in a 2D CFT

In this paper, we investigate the second and third pseudo Rényi entanglement entropies (PREE) for a locally excited state $| ψ\rangle $ and its time evolution $| ϕ\rangle = e^{- i H t} | ψ\rangle$ in a two-dimensional conformal field theory whose field content is a free massless scalar field. We consider excited states which are constructed by applying primary operators at time $t=0$, on the vacuum state. We study the time evolution of the PREE for an entangling region in the shape of finite and semi-infinite intervals at zero temperature. It is observed that the PREE is always a complex number for $t \neq 0$ and is a pure real number at $t=0$. Moreover, we discuss on its dependence on the location $x_m$ of the center of the entangling region.

hep-th↗
arXiv2023

Generalized Volume-Complexity For Two-Sided Hyperscaling Violating Black Branes

In this paper, we investigate generalized volume-complexity $\mathcal{C}_{\rm gen}$ for a two-sided uncharged HV black brane in $d+2$ dimensions. This quantity which was recently introduced in [arXiv:2111.02429], is an extension of volume in the Complexity=Volume (CV) proposal, by adding higher curvature corrections with a coupling constant $λ$ to the volume functional. We numerically calculate the growth rate of $\mathcal{C}_{\rm gen}$ for different values of the hyperscaling violation exponent $θ$ and dynamical exponent $z$. It is observed that $\mathcal{C}_{\rm gen}$ always grows linearly at late times provided that we choose $λ$ properly. Moreover, it approaches its late time value from below. For the case $λ=0$, we find an analytic expression for the late time growth rate for arbitrary values of $θ$ and $z$. However, for $λ\neq 0$, the late time growth rate can only be calculated analytically for some specific values of $θ$ and $z$. We also examine the dependence of the growth rate on $d$, $θ$, $z$ and $λ$. Furthermore, we calculate the complexity of formation obtained from volume-complexity and show that it is not UV divergent. We also examine its dependence on the thermal entropy and temperature of the black brane. At the end, we also numerically calculate the growth rate of $\mathcal{C}_{\rm gen}$ for the case where the higher curvature corrections are a linear combination of the Ricci scalar, square of the Ricci tensor and square of the Riemann tensor. We show that for appropriate values of the coupling constants, the late time growth rate is again linear.

hep-th↗
arXiv2022

Entropy of Hawking Radiation for Two-Sided Hyperscaling Violating Black Branes

In this paper, we study the von Neumann entropy of Hawking radiation $S_{\rm R}$ for a $d+2$-dimensional Hyperscaling Violating (HV) black brane which is coupled to two Minkowski spacetimes as the thermal baths. We consider two different situations for the matter fields: First, the matter fields are described by a $CFT_{d+2}$ whose central charge $c$ is very large. Second, they are described by a d+2 dimensional HV QFT which has a holographic gravitational theory that is a HV geometry at zero temperature. For both cases, we calculate the Page curve of the Hawking radiation as well as the Page time $t_{\rm Page}$. For the first case, $S_{\rm R}$ grows linearly with time before the Page time and saturates after this time. Moreover, $t_{\rm Page}$ is proportional to $\frac{2 S_{\rm th}}{c T}$, where $S_{\rm th}$ and $T$ are the thermal entropy and temperature of the black brane. For the second case, when the hyperscaling violation exponent $θ_m$ of the matter fields is zero, the results are very similar to those for the first case. However, when $θ_m \neq 0$, the entropy of Hawking radiation grows exponentially before $t_{\rm Page}$ and saturates after this time. Furthermore, the Page time is proportional to $\log \left( \frac{1}{G_{\rm N,r}} \right) $, where $G_{\rm N,r}$ is the renormalized Newton's constant. It was also observed that for both cases, $t_{\rm Page}$ is a decreasing and an increasing function of the dynamical exponent $z$ and hyperscaling violation exponent $θ$ of the black brane geometry, respectively. Moreover, for the second case, $t_{\rm Page}$ is independent of $z_m$, and for $θ_m \neq 0$, it is a decreasing function of $θ_m$.

hep-th↗
arXiv2021

Aspects of Hyperscaling Violating Geometries at Finite Cutoff

Recently, it was proposed that a $T\overline{T}$ deformed CFT is dual to a gravity theory in an asymptotically AdS spacetime at finite radial cutoff. Motivated by this proposal, we explore some aspects of Hyperscaling Violating geometries at finite cutoff and zero temperature. We study holographic entanglement entropy, mutual information (HMI) and entanglement wedge cross section (EWCS) for entangling regions in the shape of strips. It is observed that the HMI shows interesting features in comparison to the very small cutoff case: It is a decreasing function of the cutoff. It is finite when the distance between the two entangling regions goes to zero. The location of its phase transition also depends on the cutoff, and decreases by increasing the cutoff. On the other hand, the EWCS is a decreasing function of the cutoff. It does not show a discontinuous phase transition when the HMI undergoes a first-order phase transition. However, its concavity changes. Moreover, it is finite when the distance between the two strips goes to zero. Furthermore, it satisfies the bound $ E_W \geq \frac{I}{2}$ for all values of the cutoff.

hep-th↗
arXiv2020

Regularizations of Action-Complexity for a Pure BTZ Black Hole Microstate

In the action-complexity proposal there are two different methods to regularize the gravitational on-shell action, which are equivalent in the framework of AdS/CFT. In this paper, we want to study the equivalence of them for a pure BTZ black hole microstate. The microstate is obtained from a two-sided BTZ black hole truncated by a dynamical timelike ETW brane. Moreover, it is dual to a finite energy pure state in a two-dimensional CFT. We show that if one includes the timelike counterterms inspired by holographic renormalization as well as the Gibbons-Hawking-York term on the timelike boundary of the WDW patch, which exists in one of the regularizations, the coefficients of the UV divergent terms of action-complexity in the two methods become equal to each other. Furthermore, we compare the finite terms of action-complexity in both regularizations, and show that when the UV cutoff surface is close enough to the asymptotic boundary of the bulk spacetime, action-complexities in both regularizations become exactly equal to each other.

hep-th↗
arXiv2019

On the Role of Counterterms in Holographic Complexity

We consider the Complexity=Action (CA) proposal in Einstein gravity and investigate new counterterms which are able to remove all the UV divergences of holographic complexity. We first show that the two different methods for regularizing the gravitational on-shell action proposed in Ref. \cite{Carmi:2016wjl} are completely equivalent, provided that one considers the Gibbons-Hawking-York term as well as new counterterms inspired from holographic renormalization on timelike boundaries of the WDW patch. Next, we introduce new counterterms on the null boundaries of the WDW patch for four and five dimensional asymptotically AdS spacetimes which are able to remove all the UV divergences of the on-shell action. Moreover, they are covariant and do not change the equations of motion. At the end, by applying the null counterterms, we calculate the holographic complexity of an AdS-Schwarzschild black hole as well as the complexity of formation. We show that the null counterterms do not change the complexity of formation.

hep-th↗
arXiv2016

Non-local Probes in Holographic Theories with Momentum Relaxation

We consider recently introduced solutions of Einstein gravity with minimally coupled massless scalars. The geometry is homogeneous, isotropic and asymptotically anti de-Sitter while the scalar fields have linear spatial-dependent profiles. The spatially-dependent marginal operators dual to scalar fields cause momentum dissipation in the deformed dual CFT. We study the effect of these marginal deformations on holographic entanglement measures and Wilson loop. We show that the structure of the universal terms of entanglement entropy for d(>2)-dim deformed CFTs is corrected depending on the geometry of the entangling regions. In d = 2 case, the universal term is not corrected while momentum relaxation leads to a non-critical correction. We also show that decrease of the correlation length causes: the phase transition of holographic mutual information to happen at smaller separations and the confinement/deconfinement phase transition to take place at smaller critical lengths. The effective potential between point like external objects also gets corrected. We show that the strength of the corresponding force between these objects is an increasing function of the momentum relaxation parameter.

hep-th↗
arXiv2016

Holographic Mutual Information for Singular Surfaces

We study corner contributions to holographic mutual information for entangling regions composed of a set of disjoint sectors of a single infinite circle in three-dimensional conformal field theories. In spite of the UV divergence of holographic mutual information, it exhibits a first order phase transition. We show that tripartite information is also divergent for disjoint sectors, which is in contrast with the well-known feature of tripartite information being finite even when entangling regions share boundaries. We also verify the locality of corner effects by studying mutual information between regions separated by a sharp annular region. Possible extensions to higher dimensions and hyperscaling violating geometries is also considered for disjoint sectors.

hep-th↗
arXiv2015

Entanglement Entropy for Singular Surfaces in Hyperscaling violating Theories

We study the holographic entanglement entropy for singular surfaces in theories described holographically by hyperscaling violating backgrounds. We consider singular surfaces consisting of cones or creases in diverse dimensions. The structure of UV divergences of entanglement entropy exhibits new logarithmic terms whose coefficients, being cut-off independent, could be used to define new central charges in the nearly smooth limit. We also show that there is a relation between these central charges and the one appearing in the two-point function of the energy-momentum tensor. Finally we examine how this relation is affected by considering higher-curvature terms in the gravitational action.

hep-th↗
arXiv2011

Study of the OSV Conjecture for 4D N=2 Extremal Black Holes in Type IIB String Theory

In this survey we study the OSV conjecture for 4D N=2 extremal black holes of type IIB suprstring theory. We apply T-duality to find the generalized prepotential of the low energy limit of this superstring theory up to one-loop order in the closed string coupling. On the other hand, we calculate the tree-level and one-loop free energies of B-model topological string theory. To compare them we will explicitly show that the OSV conjecture holds for type IIB N=2 extremal black holes.

hep-th↗