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Tahereh Azizi

Publications and source records attributed to Tahereh Azizi.

13 recordsLinked to original sources
arXiv2025

Thick brane in Palatini formalism with a non-minimally coupled bulk scalar field

We study a thick brane scenario within the Palatini formulation of gravity, where the metric and affine connection are treated as independent variables. By introducing a non-minimal coupling between a bulk scalar field and the Ricci scalar, we obtain analytic solutions under a flat, four-dimensional Poincar\'e-invariant metric with a kink-like scalar configuration. The warp factor exhibits a bell-shaped profile, while the scalar potential forms a symmetric volcano-like structure, characteristic of a finite-thickness brane. The corresponding energy density is regular and localized, featuring a central peak with symmetrically placed negative minima. Through the analysis of linear tensor perturbations, we derive a Schr\"odinger-like equation with supersymmetric factorization, ensuring the absence of tachyonic modes and thus the stability of the background configuration. The effective potential also takes a volcano-like form that supports a localized graviton zero mode, confirming the recovery of four-dimensional gravity on the brane. A numerical study of the massive Kaluza--Klein spectrum reveals the progressive delocalization of massive modes into the bulk. Our results demonstrate a stable and physically consistent thick brane configuration within the Palatini gravity framework, offering new insights into gravity localization and braneworld phenomenology.

gr-qc↗
arXiv2025

Can Static Black Holes in Massive Gravity Serve as Candidates for Aschenbach-Like Phenomena?

The Aschenbach effect is widely regarded as a manifestation of two quintessential relativistic features: frame dragging and extreme spacetime curvature. Traditionally associated with rotating geometries, this non-monotonic behavior in orbital angular velocity challenges Newtonian intuition. In our previous work, however, we demonstrated that this velocity irregularity is not exclusive to spinning spacetimes. Specifically, we showed that the presence of a stable minimum in the gravitational potential, corresponding to a stable photon sphere, can reproduce Aschenbach-like behavior in static black holes as well. This observation suggests that, even in the absence of rotational frame dragging, curvature alone (if encoded through appropriate geometric extrema) may be sufficient to induce non-monotonic velocity profiles. In this study, we build upon that foundation to investigate whether black hole architectures in theories of Massive Gravity can inherently support the emergence of Aschenbach-like phenomena. Furthermore, can this Aschenbach-like phenomenon in static configurations be considered as an observable signature in the dynamics of general relativity, similar to the original Aschenbach effect in rotating spacetimes?

gr-qc↗
arXiv2023

Evolution of Gravitational Waves in Non-minimal Coupling Between Geometry and Matter Theories of Gravity

We consider some specific models of non-minimal matter-geometry coupling theories and investigate the propagation of the gravitational waves in them. Extracting the temporal evolution of the gravitational wave equation within the framework of a flat FRW universe with a perfect fluid distribution, we analyze the waveforms traveling during the time. We find that while both the amplitude and frequency of the GWs decay with time in all considered models, the rate of reduction is highly sensitive to the values of the equation of state parameter and input parameters of the considered models.

gr-qc↗
arXiv2017

Thermodynamics in f(T) gravity with nonminimal coupling to matter

In the present paper, we study the thermodynamics behavior of the field equations for the generalized f(T) gravity with an arbitrary coupling between matter and the torsion scalar. In this regard, we explore the verification of the first law of thermodynamics at the ap- parent horizon of the Friedmann-Robertson-Walker universe in two different perspectives namely the non-equilibrium and equilibrium de- scriptions of thermodynamics. Furthermore, we investigate the valid- ity of the second law of thermodynamics for both descriptions of this scenario with assumption that the temperature of matter inside the horizon is similar to that of horizon.

gr-qc↗
arXiv2017

Energy conditions in f(T) gravity with higher-derivative torsion terms

We study the energy conditions in the framework of the modi- fied gravity with higher-derivative torsional terms in the action. We discuss the viability of the model by studying the energy conditions in terms of the cosmographical parameters like Hubble, deceleration, jerk, snap and lerk parameters. In particular, We consider two spe- cific models that are proposed in literature and examine the viability bounds imposed by the weak energy condition.

gr-qc↗
arXiv2014

Cosmological Dynamics of Modified Gravity With a Non-minimal Curvature-matter Coupling

We perform a phase space analysis of a non-minimally coupled modified gravity theory with the Lagrangian density of the form $\frac{1}{2} f_{1}(R)+[1+λf_{2}(R)]{\cal{L}_{m}}$, where $f_1(R)$ and $f_2(R)$ are arbitrary functions of the curvature scalar $R$ and ${\cal{L}_{m}}$ is the matter Lagrangian density. We apply the dynamical system approach to this scenario in two particular models. In the first model we assume $f_1(R)=2R$ with a general form for $f_2(R)$ and set favorable values for effective equation of state parameter which is related to the several epochs of the cosmic evolution and study the critical points and their stability in each cosmic eras. In the second case, we allow the $f_1(R)$ to be an arbitrary function of $R$ and set $f_2(R)=2R$. We find the late time attractor solution for the model and show that this model has a late time accelerating epoch and an acceptable matter era.

gr-qc↗
arXiv2014

Wormhole Geometries In $f(R,T)$ Gravity

We study wormhole solutions in the framework of f (R,T) gravity where R is the scalar curvature, and T is the trace of the stress-energy tensor of the matter. We have obtained the shape function of the wormhole by specifying an equation of state for the matter field and imposing the flaring out condition at the throat. We show that in this modified gravity scenario, the matter threading the wormhole may satisfy the energy conditions, so it is the effective stress-energy that is responsible for violation of the null energy condition.

gr-qc↗
arXiv2009

Phantom-like effects in asymmetric brane embedding with induced gravity and the Gauss-Bonnet term in the Bulk

We construct an asymmetric braneworld embedding with induced gravity on the brane, where stringy effects are taken into account by incorporation of the Gauss-Bonnet term in the bulk action. We derive the effective Friedmann equation of the brane and then we investigate the possible realization of the phantom-like behavior in this setup. We show that in the absence of the Gauss-Bonnet term in the bulk action (a pure induced gravity scenario), the phantom-like behavior in asymmetric case can be realized in smaller redshift than the corresponding symmetric case. We show also that in the general case with curvature effect, the phantom-like behavior can be realized in two subcases: in a symmetric subcase and also in an asymmetric branch of the solutions. In either cases this phantom-like behavior happens without introducing any phantom fields neither on the brane nor in the bulk.

gr-qc↗
arXiv2009

Phantom-Like Behavior in $f(R)$-Gravity

We investigate possible realization of the phantom-like behavior in the framework of $f(R)$-gravity models where there are no phantom fields in the matter sector of the theory. By adopting some observationally reliable ansatz for $f(R)$, we show that it is possible to realize phantom-like behavior in $f(R)$-gravity without introduction of phantom fields that suffer from instabilities and violation of the null energy condition. Depending on the choice of $f(R)$, the null energy condition is fulfilled in some subspaces of each model parameter space.

gr-qc↗
arXiv2008

Bouncing universe with the non-minimally coupled quintom matter on the warped DGP Brane

We construct a quintom dark energy model with two non-minimally coupled scalar fields, one quintessence and the other phantom field, confined on the warped DGP brane. We study some important issues such as phantom divide line crossing, existence of the bouncing solutions and the stability of the solutions in this framework. We show that this model accounts for crossing of the phantom divide line and realization of the bouncing solutions. This model allows for stability of the solutions in separate regions of the $ω$-$ω'$ phase-plane.

hep-th↗
arXiv2005

Some Aspects of Minimal Length Quantum Mechanics

String theory, quantum geometry, loop quantum gravity and black hole physics all indicate the existence of a minimal observable length on the order of Planck length. This feature leads to a modification of Heisenberg uncertainty principle. Such a modified Heisenberg uncertainty principle is referred as gravitational uncertainty principle(GUP) in literatures. This proposal has some novel implications on various domains of theoretical physics. Here, we study some consequences of GUP in the spirit of Quantum mechanics. We consider two problem: a particle in an one-dimensional box and momentum space wave function for a "free particle". In each case we will solve corresponding perturbational equations and compare the results with ordinary solutions.

quant-ph↗
arXiv2005

Coherent States of Harmonic Oscillator and Generalized Uncertainty Principle

In this paper dynamics and quantum mechanical coherent states of a simple harmonic oscillator are considered in the framework of Generalized Uncertainty Principle(GUP). Equations of motion for simple harmonic oscillator are derived and some of their new implications are discussed. Then coherent states of harmonic oscillator in the case of GUP are compared with relative situation in ordinary quantum mechanics. It is shown that in the framework of GUP there is no considerable difference in definition of coherent states relative to ordinary quantum mechanics. But, considering expectation values and variances of some operators, based on quantum gravitational arguments one concludes that although it is possible to have complete coherency and vanishing broadening in usual quantum mechanics, gravitational induced uncertainty destroys complete coherency in quantum gravity and it is not possible to have a monochromatic ray in principle.

gr-qc↗