arXiv subjects

Davood Momeni

Publications and source records attributed to Davood Momeni.

At least 37 records · Page 2Linked to original sources

arXiv2023

Shadows and photon spheres in static and rotating traversable wormholes

The shadows and photon spheres are investigated for both static and rotating traversable wormholes. In particular, with a red-shift function constructed in combination with two distinct shape functions, the null geodesic equation is found to predict the light trajectory. To explore observable phenomena and gain a deeper understanding of the gravitational influences originating from wormholes, we explicitly demonstrate the shadow produced and photon spheres associated with both static and rotating traversable wormholes by taking into account the gravitational lensing effects and photon motion in strong gravitational fields. Specifically, the ray tracing of the light geodesic and profiles of the intensity around both static and rotating traversable wormholes can be accomplished.

gr-qc↗

arXiv2023

Rotating traversable wormhole geometries in the presence of three-form fields

In this work, we study the rotating wormhole geometries supported by a three-form field. We demonstrate for particular choices of parameters that it is possible for the matter fields threading the wormhole to satisfy the null and weak energy conditions throughout the spacetime, when the three-form field is present. In this case, the form field is interpreted as supporting the wormhole and all the exoticity is confined to it. Thus, the three-form curvature terms, which may be interpreted as a gravitational fluid, sustain these wormhole geometries. Additionally, we also address the ergoregion of the solutions.

gr-qc↗

arXiv2023

Nonminimally-coupled warm Higgs inflation: Metric vs. Palatini Formulations

In this work, we study the non-minimally-coupled Higgs model in the context of warm inflation scenario on both metric and Palatini approaches. We particularly consider a dissipation parameter of the form $Γ=C_{T}T$ with $C_{T}$ being a coupling parameter and focus only on the strong regime of the interaction between inflaton and radiation fluid. We compute all relevant cosmological parameters and constrain the models using the observational Planck 2018 data. We discover that the $n_s$ and $r$ values are consistent with the observational bounds. Having used the observational data, we constrain a relation between $ξ$ and $λ$ for the non-minimally-coupled warm Higgs inflation in both metric and Palatini cases. To produce $n_s$ and $r$ in agreement with observation, we find that their values are two orders of magnitude higher than those of the usual (cold) non-minimally-coupled Higgs inflation.

gr-qc↗

arXiv2021

Exact Solutions of (deformed) Jackiw-Teitelboim Gravity

It is well known that Jackiw-Teitelboim (JT) gravity posses the simplest theory on 2-dimensional gravity. The model has been fruitfully studied in recent years. In the present work, we investigate exact solutions for both JT and deformed JT gravity recently proposed in the literature. We revisit exact Euclidean solutions for Jackiw-Teitelboim gravity using all the non-zero components of the dilatonic equations of motion using proper integral transformation over Euclidean time coordinate. More precisely, we study exact solutions for hyperbolic coverage, cusp geometry and another compact sector of the AdS$_2$ spacetime manifold.

hep-th↗

arXiv2021

Fold bifurcation entangled surfaces for one-dimensional Kitaev lattice model

We investigate feasible holography with the Kitaev model using dilatonic gravity in AdS$_2$. We propose a generic dual theory of gravity in the AdS$_2$ and suggest that this bulk action is a suitable toy model in studying quantum mechanics in the Kitaev model using gauge/gravity duality. This gives a possible equivalent description for the Kitaev model in the dual gravity bulk. Scalar and tensor perturbations are investigated in detail. In the case of near AdS perturbation, we show that the geometry still "freezes" as is AdS, while the dilation perturbation decays at the AdS boundary safely. The time-dependent part of the perturbation is an oscillatory model. We discover that the dual gravity induces an effective and renormalizable quantum action. The entanglement entropy for bulk theory is computed using extremal surfaces. We prove that these surfaces have a fold bifurcation regime of criticality. Our approach shows directly that chaos in AdS$_2$ can be understood via fold bifurcation minimal surfaces.

hep-th↗

arXiv2020

On Nash theory of gravity with matter contents

Although it was proved that the Nash theory doesn't have classical Einstein limits, it has been proven to be formally divergent free and considered to be of interest in constructing theories of quantum gravity. The original Nash gravity without matter contents can't explain the current accelerated expansion of the Universe. A possible extension of theory is by adding some matter contents to the model. In this work, we generalize the Nash theory of gravity by adding the matter fields. In order to examine the effects of this generalization, we first derive the equations of motion in the flat FLRW spacetime and examine the behaviors of the solutions by invoking specific forms of the Hubble parameter. We also classify the physical behaviors of the solutions by employing the stability analysis and check the consistency of the model by considering particular cosmological parameters.

gr-qc↗

arXiv2020

Real Classical Geometry with arbitrary deficit parameter(s) $α(_{I})$ in Deformed Jackiw-Teitelboim Gravity

An interesting deformation of the Jackiw-Teitelboim (JT) gravity has been proposed by Witten by adding a potential term $U(ϕ)$ as a self-coupling of the scalar dilaton field. During calculating the path integral over fields, a constraint comes from integration over $ϕ$ as $R(x)+2=2αδ(\vec{x}-\vec{x}')$. The resulting Euclidean metric suffered from a conical singularity at $\vec{x}=\vec{x}'$. A possible geometry modeled locally in polar coordinates $(r,φ)$ by $ds^2=dr^2+r^2dφ^2,φ\cong φ+2π-α$. In this letter we showed that there exists another family of "exact" geometries for arbitrary values of the $α$. A pair of exact solutions are found for the case of $α=0$. One represents the static patch of the AdS and the other one is the non static patch of the AdS metric. These solutions were used to construct the Green function for the inhomogeneous model with $α\neq 0$. We address a type of the phase transition between different patches of the AdS in theory because of the discontinuity in the first derivative of the metric at $x=x'$. We extended the study to the exact space of metrics satisfying the constraint $R(x)+2=2\sum_{i=1}^{k}α_iδ^{(2)}(x-x'_i)$ as a modulo diffeomorphisms for an arbitrary set of the deficit parameters $(α_1,α_2,..,α_k)$. The space is the moduli space of Riemann surfaces of genus $g$ with $k$ conical singularities located at $x'_k$ denoted by $\mathcal{M}_{g,k}$.

hep-th↗

arXiv2020

Unrivaled Quantum Vacuum in the Primordial Universe

In a primordial universe pre(post)-inflationary era , there could be phases of early universe made of cold gas baryons, radiation and early post inflationary cosmological constant. I showed that in the baryonic epoch, the quantum vacuum is unique. By using the standard quantization scheme for a massive minimally coupled scalar field with maximal conformal symmetry in the classical spacetime, I demonstrated that the scalar modes had an effective mass $m_{eff}^2\approx 0$ (or $m_{eff}^2\approx constant$). This argument validated when the conformal time $η$ kept so close to the inflation ending time $η=η_c$. The energy density of the baryonic matter diverged at the inflation border and vanishes at the late time future. Furthermore I argued that at very early accelerating epoch when the radiation was the dominant part in the close competition with the early time cosmological constant, fine tuned mass of the scalar field $m\propto \sqrtΛ$ also provided a unique quantum vacuum. The reason is that the effective mass eventually is vanished. A remarkable observation was that all the other possible vacuum states "squeezed" eternally.

gr-qc↗

arXiv2020

Position-Dependent Mass Quantum systems and ADM formalism

The classical Einstein-Hilbert (EH) action for general relativity (GR) is shown to be formally analogous to the classical system with position-dependent mass (PDM) models. The analogy is developed and used to build the covariant classical Hamiltonian as well as defining an alternative phase portrait for GR. The set of associated Hamilton's equations in the phase space is presented as a first-order system dual to the Einstein field equations. Following the principles of quantum mechanics, I build a canonical theory for the classical general. A fully consistent quantum Hamiltonian for GR is constructed based on adopting a high dimensional phase space. It is observed that the functional wave equation is timeless. As a direct application, I present an alternative wave equation for quantum cosmology. In comparison to the standard Arnowitt-Deser-Misner(ADM) decomposition and quantum gravity proposals, I extended my analysis beyond the covariant regime when the metric is decomposed into the $3+1$ dimensional ADM decomposition. I showed that an equal dimensional phase space can be obtained if one applies ADM decomposed metric.

physics.gen-ph↗

arXiv2019

Covariant Quantum-Mechanical Scattering via Stueckelberg-Horwitz-Piron Theory

Based on the Stueckelberg-Horwitz-Piron theory of covariant quantum mechanics on curved spacetime, we solved wave equation for a charged covariant harmonic oscillator in the background of charged static spherically symmetric black hole. Using Greens functions , we found asymptotic form for the wave function in the lowest mode (s-mode) and in higher moments. It has been proven that for s-wave, in a definite range of solid angles, the differential cross section depends effectively to the magnetic and electric charges of the black hole.

physics.gen-ph↗

arXiv2019

Bose-Einstein Condensation for an Exponential Density of States Function and Lerch Zeta Function

I show how Bose-Einstein condensation (BEC) in a non interacting bosonic system with exponential density of states function yields to a new class of Lerch zeta functions. By looking on the critical temperature, I suggest that a possible strategy to prove the "Riemann hypothesis" problem. In a theorem and a lemma I suggested that the classical limit $\hbar\to 0$ of BEC can be used as a tool to find zeros of real part of the Riemann zeta function with complex argument. It reduces the Riemann hypothesis to a softer form. Furthermore I propose a pair of creation-annihilation operators for BEC phenomena. This set of creation-annihilation operators is defined on a complex Hilbert space. They build a set up to interpret this type of BEC as a creation-annihilation phenomenon for a virtual hypothetical particle.

cond-mat.stat-mech↗

arXiv2019

Chaos in balanced and unbalanced holographic s+p superconductors

In this work, we propose a toy model for a mixture of superconductors with competitive s and p modes using gauge/gravity duality. We demonstrate that the model undergoes phase transitions with the proper choice of different values for chemical potentials. We consider both balanced and unbalanced cases. We propose that the condensate field in the bulk toy model for a mixing s+p phase of high temperature superconductors undergoes a chaotic phase space scenario. Using a suitable measure function for chaos, we demonstrate the existence of chaotic dynamics via condensate fields. As an alternative method, we also investigate the phase portrait in the extended phase space for the condensates.

hep-th↗

arXiv2019

Quantum Information metric for time-dependent quantum systems and higher-order corrections

It is well established that quantum criticality is one of the most intriguing phenomena which signals the presence of new states of matter. Without prior knowledge of the local order parameter, the quantum information metric (or fidelity susceptibility) can indicate the presence of a phase transition as well as it measures distance between quantum states. In this work, we calculate the distance between quantum states which is equal to the fidelity susceptibility in quantum model for a time-dependent system describing a two-level atom coupled to a time-driven external field. As inspired by the Landau-Zener quantum model, we find in the present work information metric induced by fidelity susceptibility. We, for the first time, derive a higher-order rank-3 tensor as a third-order fidelity susceptibility. Having computed quantum noise function in this simple time-dependent model we show that the noise function eternally lasts long in our model.

quant-ph↗

arXiv2019

On gravitational wave modes in Nash theory of gravity

In this Letter, we consider original Nash theory of gravity. In terms of the scalar fields representation, Nash gravity is equivalent to the action of bi-scalar tensor gravity with four derivative terms of metric tensor. We then quantify the ghost in the theory. In order to study the gravitational wave modes of the theory, we perform a small perturbation over a fixed Minkowski background. We discover the standard wave equation and obtain the solutions as those of the standard general relativity. In order to satisfy the GR in the weak field limit, we further modify the original Nash theory by adding the Einstein-Hibert term called modified Nash gravity. In this theory, we once study the gravitational wave modes. We derive equations of motion and examine the solutions. We discover the two-mode solutions: the massless graviton and the massive one. Using a uniform prior probability on the graviton mass, we can constrain mass parameter.

gr-qc↗

arXiv2019

Exact Classical and Quantum Solutions for a Covariant Oscillator Near the Black Hole Horizon in Stueckelberg-Horwitz-Piron Theory

We found exact solutions for canonical classical and quantum dynamics for general relativity in Horwitz general covarience theory. These solutions can be obtained by solving the generalized geodesic equation and Schrödinger-Stueckelberg -Horwitz-Piron (SHP) wave equation for a simple harmonic oscilator in the background of a two dimensional dilaton black hole spacetime metric. We proved the existence of an orthonormal basis of eigenfunctions for generalized wave equation. This basis functions form an orthogonanl and normalized (orthonormal) basis for an appropriate Hilbert space. The energy spectrum has a mixed spectrum with one conserved momentum $p$ according to a quantum number $n$. To find the ground state energy we used a variational method with appropriate boundary conditions. A set of mode decomposed wave functions and calculated for the Stueckelberg-Schrodinger equation on a general five dimensional blackhole spacetime in Hamilton gauge.

gr-qc↗

arXiv2018

Universality of Short Distance Corrections to Quantum Optics

As quantum optical phenomena are based on Maxwell's equations, and it is becoming important to understand quantum optical phenomena at short distances, so it is important to analyze quantum optics using short distance corrected Maxwell's equation. Maxwell's action can be obtained from quantum electrodynamics using the framework of effective field theory, and so the leading order short distance corrections to Maxwell's action can also be obtained from the derivative expansion of the same effective field theory. Such short distance corrections will be universal for all quantum optical systems, and they will effect all short distance quantum optical phenomena. In this paper, we will analyze the form of such corrections, and demonstrate the standard formalism of quantum optics can still be used (with suitable modifications), to analyze quantum optical phenomena from this short distance corrected Maxwell's actions.

quant-ph↗

arXiv2018

Thermodynamic and Holographic Information Dual to Volume

In this paper, we will analyze the connection between the fidelity susceptibility, the holographic complexity and the thermodynamic volume. We will regularize the fidelity susceptibility and the holographic complexity by subtracting the contribution of the background AdS spacetime from the deformation of the AdS spacetime. It will be demonstrated that this regularized fidelity susceptibility has the same behavior as the thermodynamic volume and that the regularized complexity has a very different behavior. As the information dual to different volumes in the bulk would be measured by the fidelity susceptibility and the holographic complexity, this paper will establish a connection between thermodynamics and information dual to a volume.

hep-th↗

arXiv2018

Phase Space description of Nonlocal Teleparallel Gravity

We study cosmological solutions in nonlocal teleparallel gravity or $f(T)$ theory, where $T$ is the torsion scalar in teleparallel gravity. This is a natural extenstion of the usual teleparallel gravity with nonlocal terms. In this work the phase space portrait proposed to describe the dynamics of an arbitrary flat, homogeneous cosmological background with a number of matter contents, both in early and late time epochs. The aim was to convert the system of the equations of the motion to a first order autonomous dynamical system and to find fixed points and attractors using numerical codes. For this purpose, firstly we derive effective forms of cosmological field equations describing the whole cosmic evolution history in a homogeneous and isotropic cosmological background and construct the autonomous system of the first order dynamical equations. In addition, we investigate the local stability in the dynamical systems called "the stable/unstable manifold" by introducing a specific form of the interaction between matter, dark energy, radiation and a scalar field. Furthermore, we explore the exact solutions of the cosmological equations in the case of de Sitter spacetime. In particular, we examine the role of an auxiliary function called "gauge" $η$ in the formation of such cosmological solutions and show whether the de Sitter solutions can exist or not. Moreover, we study the stability issue of the de Sitter solutions both in vacuum and non-vacuum spacetimes. It is demonstrated that for nonlocal $f(T)$ gravity, the stable de Sitter solutions can be produced even in vacuum spacetime.

gr-qc↗