scholarly journals Energy conditions in non-local gravity

2019 ◽  
Vol 16 (10) ◽  
pp. 1950149 ◽  
Author(s):  
M. Ilyas
Keyword(s):  
Power Law ◽  
Arbitrary Function ◽  
Energy Conditions ◽  
De Sitter ◽  
Sitter Solution ◽  
Local Gravity ◽  
Non Local

We investigate the different energy conditions in non-local gravity, which is obtained by adding an arbitrary function of d’Alembertian operator, [Formula: see text], to the Hilbert–Einstein action. We analyze the validity of four different energy conditions and illustrate the different constraints over parameters of the power-law solution as well as de Sitter solution.

scholarly journals De Sitter and power-law solutions in non-local Gauss–Bonnet gravity

2018 ◽  
Vol 15 (11) ◽  
pp. 1850188 ◽  
Author(s):  
E. Elizalde ◽  
S. D. Odintsov ◽  
E. O. Pozdeeva ◽  
S. Yu. Vernov
Keyword(s):  
Power Law ◽  
Sufficient Conditions ◽  
Model Parameters ◽  
Local Form ◽  
De Sitter ◽  
Dynamical Equations ◽  
Non Local ◽  
Necessary And Sufficient ◽  
The Universe ◽  
Universe Evolution

The cosmological dynamics of a non-locally corrected gravity theory, involving a power of the inverse d’Alembertian, is investigated. Casting the dynamical equations into local form, the fixed points of the models are derived, as well as corresponding de Sitter and power-law solutions. Necessary and sufficient conditions on the model parameters for the existence of de Sitter solutions are obtained. The possible existence of power-law solutions is investigated, and it is proven that models with de Sitter solutions have no power-law solutions. A model is found, which allows to describe the matter-dominated phase of the Universe evolution.

scholarly journals Energy Conditions and Constraints on the Generalized Non-Local Gravity Model

2017 ◽  
Vol 34 (7) ◽  
pp. 079801 ◽  
Author(s):  
Ya-Bo Wu ◽  
Xue Zhang ◽  
Bo-Hai Chen ◽  
Nan Zhang ◽  
Meng-Meng Wu
Keyword(s):  
Gravity Model ◽  
Energy Conditions ◽  
Local Gravity ◽  
Non Local

scholarly journals Cosmological reconstruction and energy constraints in generalized Gauss–Bonnet-scalar–kinetic–matter couplings

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Adam Z. Kaczmarek ◽  
Dominik Szczęśniak
Keyword(s):  
Scalar Field ◽  
Perfect Fluid ◽  
Power Law ◽  
Cosmological Models ◽  
Energy Conditions ◽  
Kinetic Term ◽  
De Sitter ◽  
Field Equations ◽  
Energy Constraints ◽  
Matter Fields

Abstract Recently introduced $$f(\mathcal {G},T)$$ f ( G , T ) theory is generalized by adding dependence on the arbitrary scalar field $$\phi $$ ϕ and its kinetic term $$(\nabla \phi )^2$$ ( ∇ ϕ ) 2 , to explore non-minimal interactions between geometry, scalar and matter fields in context of the Gauss–Bonnet theories. The field equations for the resulting $$f\left( \mathcal {G},\phi ,(\nabla \phi )^2,T\right) $$ f G , ϕ , ( ∇ ϕ ) 2 , T theory are obtained and show that particles follow non-geodesic trajectories in a perfect fluid surrounding. The energy conditions in the Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime are discussed for the generic function $$f\left( \mathcal {G},\phi ,(\nabla \phi )^2,T\right) $$ f G , ϕ , ( ∇ ϕ ) 2 , T . As an application of the introduced extensions, using the reconstruction techniques we obtain functions that satisfy common cosmological models, along with the equations describing energy conditions for the reconstructed $$f\left( \mathcal {G},\phi ,(\nabla \phi )^2,T\right) $$ f G , ϕ , ( ∇ ϕ ) 2 , T gravity. The detailed discussion of the energy conditions for the de Sitter and power-law spacetimes is provided in terms of the fixed kinetic term i.e. in the $$f\left( \mathcal {G},\phi ,T\right) $$ f G , ϕ , T case. Moreover, in order to check viability of the reconstructed models, we discuss the energy conditions in the specific cases, namely the $$f(R,\phi ,(\nabla \phi )^2)$$ f ( R , ϕ , ( ∇ ϕ ) 2 ) and $$f=\gamma (\phi ,X)\mathcal {G}+\mu T^{1/2}$$ f = γ ( ϕ , X ) G + μ T 1 / 2 approaches. We show, that for the appropriate choice of parameters and constants, the energy conditions can be satisfied for the discussed scenarios.

scholarly journals Energy condition in unimodular f(R, T) gravity

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
Fateme Rajabi ◽  
Kourosh Nozari
Keyword(s):  
Power Law ◽  
Energy Condition ◽  
Energy Conditions ◽  
Energy Tensor ◽  
De Sitter ◽  
Stress Energy Tensor ◽  
Modified Gravity Theory ◽  
Stress Energy ◽  
The Stability ◽  
Interesting Alternative

AbstractWe study an interesting alternative of modified gravity theory, namely, the unimodular f(R, T) gravity in which R is the Ricci scalar and T is the trace of the stress–energy tensor. We study the viability of the model by using the energy conditions. We discuss the strong, weak, null and dominant energy conditions in terms of deceleration, jerk and snap parameters. We investigate energy conditions for reconstructed unimodular f(R, T) models and give some constraints on the parametric space of the model. We observe that by setting appropriately free parameters, energy conditions can be satisfied. Furthermore, we study the stability of the solutions in perturbations framework. In this case, we investigate stability conditions for de Sitter and power law solutions and we examine viability of cosmological evolution of these perturbations. The results show that for some values of the input parameters, for which energy conditions are satisfied, de Sitter and power-law solutions may be stable.

scholarly journals Traversable wormholes in Einsteinian cubic gravity

2019 ◽  
Vol 35 (06) ◽  
pp. 2050017 ◽  
Author(s):  
Mohammad Reza Mehdizadeh ◽  
Amir Hadi Ziaie
Keyword(s):  
Equation Of State ◽  
Gravitational Lensing ◽  
Energy Condition ◽  
Higher Order ◽  
Energy Conditions ◽  
Geodesic Motion ◽  
De Sitter ◽  
Asymptotically Flat ◽  
Traversable Wormholes ◽  
Standard Energy

In this work, we investigate wormhole configurations described by a constant redshift function in Einstein-Cubic gravity ( ECG ). We derive analytical wormhole geometries by assuming a particular equation of state ( EoS ) and investigate the possibility that these solutions satisfy the standard energy conditions. We introduce exact asymptotically flat and anti-de Sitter (AdS) spacetimes that admit traversable wormholes. These solutions are obtained by imposing suitable values for the parameters of the theory so that the resulted geometries satisfy the weak energy condition ( WEC ) in the vicinity of the throat, due to the presence of higher-order curvature terms. Moreover, we find that AdS solutions satisfy the WEC throughout the spacetime. A description of the geodesic motion of time-like and null particles is presented for the obtained wormhole solutions. Also, using gravitational lensing effects, observational features of the wormhole structure are discussed.

scholarly journals Non-local criteria for the borehole problem: Gradient Elasticity versus Finite Fracture Mechanics

Meccanica ◽  
2021 ◽  
Author(s):  
A. Sapora ◽  
G. Efremidis ◽  
P. Cornetti
Keyword(s):  
Stress Concentration ◽  
Fracture Mechanics ◽  
Elastic Material ◽  
Fracture Criterion ◽  
Biaxial Loading ◽  
Gradient Elasticity ◽  
Energy Conditions ◽  
Material Behaviour ◽  
Finite Fracture Mechanics ◽  
Non Local

AbstractTwo nonlocal approaches are applied to the borehole geometry, herein simply modelled as a circular hole in an infinite elastic medium, subjected to remote biaxial loading and/or internal pressure. The former approach lies within the framework of Gradient Elasticity (GE). Its characteristic is nonlocal in the elastic material behaviour and local in the failure criterion, hence simply related to the stress concentration factor. The latter approach is the Finite Fracture Mechanics (FFM), a well-consolidated model within the framework of brittle fracture. Its characteristic is local in the elastic material behaviour and non-local in the fracture criterion, since crack onset occurs when two (stress and energy) conditions in front of the stress concentration point are simultaneously met. Although the two approaches have a completely different origin, they present some similarities, both involving a characteristic length. Notably, they lead to almost identical critical load predictions as far as the two internal lengths are properly related. A comparison with experimental data available in the literature is also provided.

scholarly journals HELICAL MAGNETIC FIELDS FROM INFLATION

2009 ◽  
Vol 18 (09) ◽  
pp. 1395-1411 ◽  
Author(s):  
LEONARDO CAMPANELLI
Keyword(s):  
Magnetic Fields ◽  
Power Law ◽  
Background Field ◽  
Wave Number ◽  
Conformal Time ◽  
De Sitter ◽  
Simple Power ◽  
Dimensionless Constant ◽  
Real Positive Number

We analyze the generation of seed magnetic fields during de Sitter inflation considering a noninvariant conformal term in the electromagnetic Lagrangian of the form [Formula: see text], where I(ϕ) is a pseudoscalar function of a nontrivial background field ϕ. In particular, we consider a toy model that could be realized owing to the coupling between the photon and either a (tachyonic) massive pseudoscalar field or a massless pseudoscalar field nonminimally coupled to gravity, where I follows a simple power law behavior I(k,η) = g/(-kη)β during inflation, while it is negligibly small subsequently. Here, g is a positive dimensionless constant, k the wave number, η the conformal time, and β a real positive number. We find that only when β = 1 and 0.1 ≲ g ≲ 2 can astrophysically interesting fields be produced as excitation of the vacuum, and that they are maximally helical.

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