scholarly journals A new model of nonlocal modified gravity

2013 ◽  
Vol 94 (108) ◽  
pp. 187-196 ◽  
Author(s):  
Ivan Dimitrijevic ◽  
Branko Dragovich ◽  
Jelena Grujic ◽  
Zoran Rakic
Keyword(s):  
Gravity Model ◽  
Modified Gravity ◽  
Nonlocal Term ◽  
New Model ◽  
Cosmological Solutions

We consider a new modified gravity model with nonlocal term of the form R?1F(?)R. This kind of nonlocality is motivated by investigation of applicability of a few unusual ansatze to obtain some exact cosmological solutions. In particular, we find attractive and useful quadratic ansatz ?R = qR2.

scholarly journals Some cosmological solutions of a nonlocal modified gravity

Filomat ◽  
2015 ◽  
Vol 29 (3) ◽  
pp. 619-628 ◽  
Author(s):  
Ivan Dimitrijevic ◽  
Branko Dragovich ◽  
Jelena Grujic ◽  
Zoran Rakic
Keyword(s):  
Gravitational Field ◽  
Modified Gravity ◽  
Riemannian Geometry ◽  
Equations Of Motion ◽  
Nonlocal Term ◽  
Action Functional ◽  
Einstein Theory ◽  
Metric Tensor ◽  
Differentiable Functions ◽  
Cosmological Solutions

We consider nonlocal modification of the Einstein theory of gravity in framework of the pseudo- Riemannian geometry. The nonlocal term has the form H(R)F(?)G(R), where H and G are differentiable functions of the scalar curvature R, and F(?) = ??n=0 fn?n is an analytic function of the d?Alambert operator ?. Using calculus of variations of the action functional, we derived the corresponding equations of motion. The variation of action is induced by variation of the gravitational field, which is the metric tensor g?v. Cosmological solutions are found for the case when the Ricci scalar R is constant.

Multi Depot Vehicle Routing Using Ant Colony Optimization - Trip Assignment of Freight Flow Using Modified Gravity Model

2021 ◽  
Author(s):  
Husnain Saeed ◽  
Shahid Ikramullah ◽  
Mushtaq Khan ◽  
Fahd Amjad ◽  
Liaqat Ali ◽  
...  
Keyword(s):  
Ant Colony Optimization ◽  
Vehicle Routing ◽  
Gravity Model ◽  
Modified Gravity ◽  
Ant Colony ◽  
Freight Flow

scholarly journals A new f(R) gravity model and properties of gravitational waves in it

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Dhruba Jyoti Gogoi ◽  
Umananda Dev Goswami
Keyword(s):  
Gravitational Waves ◽  
Gravity Model ◽  
Longitudinal Mode ◽  
Mass Scale ◽  
Gravity Models ◽  
Jordan Frame ◽  
New Model ◽  
Existing Problems ◽  
Pulsar Timing ◽  
New Directions

AbstractIn this paper, we have introduced a new f(R) gravity model as an attempt to have a model with more parametric control, so that the model can be used to explain the existing problems as well as to explore new directions in physics of gravity, by properly constraining it with recent observational data. Here basic aim is to study the properties of Gravitational Waves (GWs) in this new model. In f(R) gravity metric formalism, the model shows the existence of scalar degree of freedom as like other f(R) gravity models. Due to this reason, there is a scalar mode of polarization of GWs present in the theory. This polarization mode exists in a mixed state, of which one is transverse massless breathing mode with non-vanishing trace and the other is massive longitudinal mode. The longitudinal mode being massive, travels at speed less than the usual tensor modes found in General Relativity (GR). Moreover, for a better understanding of the model, we have studied the potential and mass of scalar graviton in both Jordan frame and Einstein frame. This model can pass the solar system tests and can explain primordial and present dark energy. Also, we have put constraints on the model. It is found that the correlation function for the third mode of polarization under certain mass scale predicted by the model agrees well with the recent data of Pulsar Timing Arrays. It seems that this new model would be useful in dealing with different existing issues in the areas of astrophysics and cosmology.

scholarly journals Some Cosmological Solutions of a New Nonlocal Gravity Model

Symmetry ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 917
Author(s):  
Ivan Dimitrijevic ◽  
Branko Dragovich ◽  
Alexey S. Koshelev ◽  
Zoran Rakic ◽  
Jelena Stankovic
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Analytic Function ◽  
Cosmological Constant ◽  
Explicit Form ◽  
Gravity Model ◽  
Necessary Conditions ◽  
Equations Of Motion ◽  
Nonlocal Operator ◽  
Cosmological Solutions

In this paper, we investigate a nonlocal modification of general relativity (GR) with action S = 1 16 π G ∫ [ R − 2 Λ + ( R − 4 Λ ) F ( □ ) ( R − 4 Λ ) ] − g d 4 x , where F ( □ ) = ∑ n = 1 + ∞ f n □ n is an analytic function of the d’Alembertian □. We found a few exact cosmological solutions of the corresponding equations of motion. There are two solutions which are valid only if Λ ≠ 0 , k = 0 , and they have no analogs in Einstein’s gravity with cosmological constant Λ . One of these two solutions is a ( t ) = A t e Λ 4 t 2 , that mimics properties similar to an interference between the radiation and the dark energy. Another solution is a nonsingular bounce one a ( t ) = A e Λ t 2 . For these two solutions, some cosmological aspects are discussed. We also found explicit form of the nonlocal operator F ( □ ) , which satisfies obtained necessary conditions.

scholarly journals Cosmological solutions of F (R, T) gravity model with k -essence

2019 ◽  
Vol 1391 ◽  
pp. 012163 ◽  
Author(s):  
Koblandy Yerzhanov ◽  
Bekdaulet Meirbekov ◽  
Gulnur Bauyrzhan ◽  
Ratbay Myrzakulov
Keyword(s):  
Gravity Model ◽  
Cosmological Solutions

scholarly journals Cosmological scaling solutions with tachyon: Modified gravity model

2008 ◽  
Vol 668 (3) ◽  
pp. 182-186 ◽  
Author(s):  
A.A. Sen ◽  
N. Chandrachani Devi
Keyword(s):  
Gravity Model ◽  
Modified Gravity
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