arXiv subjects

H. Farahani

Publications and source records attributed to H. Farahani.

At least 19 recordsLinked to original sources

arXiv2024

Some Epistemic Extensions of Gödel Fuzzy Logic

In this paper we prove soundness and completeness of some epistemic extensions of Gödel fuzzy logic, based on Kripke models in which both propositions at each state and accessibility relations take values in [0,1]. We adopt belief as our epistemic operator, acknowledging that the axiom of Truth may not always hold. We propose the axiomatic system $\textbf{K}_\textbf{F}$ serves as a fuzzy variant of classical epistemic logic $\textbf{K}$, then by considering consistent belief and adding positive introspection and Truth axioms to the axioms of $\textbf{K}_\textbf{F}$, the axiomatic extensions $\textbf{B}_\textbf{F}$ and $\textbf{T}_\textbf{F}$ are established. To demonstrate the completeness of $\textbf{K}_\textbf{F}$, we present a novel approach that characterizes formulas semantically equivalent to $\perp$ and we introduce a grammar describing formulas with this property. Furthermore, it is revealed that validity in $\textbf{K}_\textbf{F}$ cannot be reduced to the class of all models having crisp accessibility relations, and also $\textbf{K}_\textbf{F}$ does not enjoy the finite model property. These properties distinguish $\textbf{K}_\textbf{F}$ as a new modal extension of Gödel fuzzy logic which differs from the standard Gödel Modal Logics $\mathcal{G}_\Box$ and $\mathcal{G}_\Diamond$ proposed by Caicedo and O. Rodriguez.

math.LO↗

arXiv2018

Quantum gravity effects on Hořava-Lifshitz black hole

In this paper, we would like to obtain quantum gravity effects by using Hořava-Lifshitz black hole. We consider logarithmic corrected thermodynamics quantities and investigate the effects of logarithmic correction term. Logarithmic correction comes from thermal fluctuation and may be interpreted as quantum loop corrections. As black hole is a gravitational system, hence we can investigate quantum gravity effect. We find such effects on the black hole stability and obtain domain of correction coefficient.

hep-th↗

arXiv2017

P-V criticality of first-order entropy corrected AdS black holes in massive gravity

We consider a massive black hole in four dimensional AdS space and study the effect of thermal fluctuations on the thermodynamics of the black hole. We consider thermal fluctuations as logarithmic correction terms in the entropy. We analyse the effect of logarithmic correction on thermodynamics potentials like Helmholtz and Gibbs which are found decreasing functions. We study critical points and stability and find that presence of logarithmic correction is necessary to have stable phase and critical point.

gr-qc↗

arXiv2016

Logarithmic corrected $F(R)$ gravity in the light of Planck 2015

In this letter, we consider the theory of $F(R)$ gravity with the lagrangian density $ £= R+αR^2 + βR^2 \ln βR $. We obtain the constant curvature solutions and find the scalar potential of the gravitational field. We also obtain the mass squared of a scalaron in the Einstein$^,$s frame. We find cosmological parameters corresponding to the recent Plank 2015 results. Finally, we analyze the critical points and stability of the new modified theory of gravity and find that logarithmic correction is necessary to have successful model.

gr-qc↗

arXiv2016

Interacting Ghost Dark Energy Models in the Higher Dimensional Cosmology

We investigate interacting ghost dark energy models in higher dimensional cosmology. We attempt to model dark matter within a barotropic fluid with $P_{b}=ω(t)_{b}ρ$. In this work we consider four different models based on choosing equation of state parameter and interaction term. We confirm that our models agree with observational data.

gr-qc↗

arXiv2014

Interacting Holographic Extended Chaplygin Gas and Phantom Cosmology in the Light of BICEP2

In this paper, we study the holographic dark energy density and interacting extended Chaplygin gas energy density in the Einstein gravity. We reconstruct the scalar field and the scalar potential describing the extended Chaplygin gas. In the special case, we obtain energy density and investigate some cosmological parameters. Assuming interaction between components we find energy density for some different parametrization of total EoS. We analyze tensor to scalar ratio and use recent observational data of BICEP2 to fix the model parameters.

gr-qc↗

arXiv2014

Interacting quintessence dark energy models in Lyra manifold

In this paper, we consider two-component dark energy models in Lyra manifold. The first component is assumed as a quintessence field while the second model may be a viscous polytropic gas, a viscous Van der Waals gas or a viscous modified Chaplygin gas. We also consider the possibility of interaction between components. By using numerical analysis, we study some cosmological parameters of the models and compare them with observational data.

gr-qc↗

arXiv2014

Mutually interacting Tachyon dark energy with variable $G$ and $Λ$

In this paper we consider Tachyonic scalar field as dark energy with interaction between components in the case of variable $G$ and $Λ$. We assume a flat Universe with specific form of scale factor and study cosmological parameters numerically and graphically. Statefinder analysis also performed as well. In the special choice of interaction parameters we succeed to obtain analytical expression of densities. We find that our model will be stable in the late stage but there is an instability at the early Universe.

gr-qc↗

arXiv2014

Dark Energy and Tachyon Field in Bianchi Type-V Space-time

In this paper, we consider Bianchi type-V space-time and study a cosmological model of dark energy based on Tachyon scalar field. We assumed three different kinds of matter without possibility of interaction with scalar dark energy. Assuming power law Hubble parameter in terms of scale factor we obtain evolution of scalar field, scalar potential and equation of state parameter.

gr-qc↗

arXiv2014

Hubble parameter corrected interactions in cosmology

In this paper we make steps in a new direction by considering fluids with EoS of more general form $F(ρ,P)=0$. It is thought that there should be interaction between cosmic fluids, but this assumption for this stage carries only phenomenological character opening a room for different kind of manipulations. In this article we will consider a modification of an interaction $Q$, where we accept that interaction parameter $b_{1}$ (order of unity) in $Q=3Hb_{1}ρ$ is time dependent and presented as a linear function of Hubble parameter $H$ of the form $b_{0}+btH$, where $b$ and $b_{0}$ are constants. We consider two different models include modified Chaplygin gas and palotropic gas which have bulk viscosity. Then, we investigate problem numerically and analyze behavior of different cosmological parameters concerning to fluids and behavior of Universe.

gr-qc↗

arXiv2014

Phenomenologically varying $Λ$ and a toy model for the Universe

We consider a model of the Universe with variable G and Λ. Subject of our interest is a phenomenological model for Λ proposed and considered in this article first time (up to our knowledge). Modification based on an assumption that ghost dark energy exists and Universe will feel it through Λ. In that case we would like to consider possibility that there exist some unusual connections between different components of the fluids existing in Universe. We would like to stress, that this is just an assumption and could be very far from the reality. We are interested by this model as a phenomenological and mathematical and unfortunately, we will not discuss about physical conditions and possibilities of having such modifications. To test our assumption and to observe behavior of the Universe, we will consider toy models filled by a barotropic fluid and modified Chaplyagin gas. To complete the logic of the research we will consider interaction between barotropic fluid or Chaplygin gas with ghost dark energy as a separate scenario. Statefinder diagnostic also provided with stability analysis of the models. All free parameters of the model fixed to satisfy generalized second law of thermodynamics.

gr-qc↗

arXiv2014

Interacting Ricci dark energy models with an effective $Λ$-term in Lyra manifold

In this paper we consider a universe filled with barotropic dark matter and Ricci dark energy in Lyra geometry with varying Lambda. We assume two different kinds of interactions between dark matter and dark energy. Then, by using numerical analysis, we investigate some cosmological parameters of the models such as equation of state, Hubble and deceleration parameters.

gr-qc↗

arXiv2014

Interaction between modified Chaplygin gas and ghost dark energy in presence of extra dimensions

In this paper, we consider three different models of dark energy in higher dimensional space-time and discuss about some cosmological parameters numerically. The first model is a single component universe including viscous varying modified Chaplygin gas. In the second model, we consider two-component universe including viscous varying modified Chaplygin gas and ghost dark energy. In the third model, we consider another two-component universe including viscous modified cosmic Chaplygin gas and ghost dark energy. In the cases of two-component fluids we also consider possibility of interaction between components.

gr-qc↗

arXiv2014

Quintessence Cosmology with an Effective $Λ$-Term in Lyra Manifold

In this paper, we study quintessence cosmology with an effective $Λ$-term in Lyra manifold. We consider three different models by choosing variable $Λ$ depend on time, the Hubble parameter and the energy density of dark matter and dark energy. Dark energy assumed as quintessence which interacts with the dark matter. By using numerical analysis we investigate behavior of cosmological parameters in three different models and compare our results with observational data. Statefinder diagnostic is also performed for all models.

gr-qc↗

arXiv2013

Rotating charged hairy black hole in (2+1) dimensions and particle acceleration

In this paper we construct rotating charged hairy black hole in (2+1) dimensions for infinitesimal black hole charge and rotation parameters. Then we consider this black hole as particle accelerator and calculate the center-of-mass energy of two colliding test particles near the rotating charged hairy black hole in (2+1) dimensions. As we expected, the center-of-mass energy has infinite value.

hep-th↗

arXiv2013

Phenomenological Fluids from Interacting Tachyonic Scalar Fields

In this paper we are interested to consider mathematical ways to obtain different phenomenological fluids from two-component Tachyonic scalar fields. We consider interaction between components and investigate problem numerically. Statefinder diagnostics and validity of the generalized second law of thermodynamics performed and checked. We suppose that our Universe bounded by Hubble horizon.

gr-qc↗

arXiv2013

Interacting Ghost Dark Energy Models with Variable $G$ and $Λ$

In this paper we consider several phenomenological models of variable $Λ$. Model of a flat Universe with variable $Λ$ and $G$ is accepted. It is well known, that varying $G$ and $Λ$ gives rise to modified field equations and modified conservation laws, which gives rise to many different manipulations and assumptions in literature. We will consider two component fluid, which parameters will enter to $Λ$. Interaction between fluids with energy densities $ρ_{1}$ and $ρ_{2}$ assumed as $Q=3Hb(ρ_{1}+ρ_{2})$. We have numerical analyze of important cosmological parameters like EoS parameter of the composed fluid and deceleration parameter $q$ of the model.

gr-qc↗

arXiv2013

Phenomenological Varying Modified Chaplygin Gas with Variable $G$ and $Λ$: Toy Models for Our Universe

This article motivated by the recent articles and results of two authors. Recently, J. Sadeghi and H. Farahani presented a work [1], where they include viscosity and analyze general model, by this way they extended models considered by M. Khurshudyan [2] and [3]. In this article, We tempt to consider varying Modified Chaplygin gas model in case of variable $G$ and $Λ$. It is well known, that varying $G$ and $Λ$ gives rise to modified field equations and modified conservation laws. We will consider two different toy models. First model is a Universe with one component phenomenological gas of our consideration, while for the second model we assume existence of a composed fluid of gas and a matter with $P=ω(t)ρ_{m}$. Sign changeable interaction between fluids is accepted. We will analyze important cosmological parameters like EoS parameter of a fluid, deceleration parameter $q$ of the model.

gr-qc↗