Non-minimal torsion-matter coupling and wormhole solutions

2018 ◽  
Vol 15 (12) ◽  
pp. 1850210 ◽  
Author(s):  
Abdul Jawad ◽  
H. Moradpour
Keyword(s):  
Energy Density ◽  
Equilibrium Phase ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Minimal Coupling ◽  
Linear Forms ◽  
Torsion Scalar ◽  
Matter Coupling ◽  
Free Parameters ◽  
Modified Theory

Taking into account various energy density models in the framework of torsion-based modified theory, some wormhole solutions are derived and studied. We use a non-minimal coupling between matter and torsion in order to construct the wormhole geometry for constant, exponential and Lorentzian energy density models. Two sets of torsion dependent models, including (i) teleparalell case with linear forms of torsion scalar and (ii) a [Formula: see text] gravity with quadratic form of torsion scalar, have been considered throughout this paper. Our study shows that additional terms to the Einstein field equations, due to consider modified gravity, give us the opportunity of obtaining wormhole solutions which may be supported by baryonic sources. We also check the equilibrium phase of the wormhole solutions using anisotropic and hydrostatic forces. The details of the obtained results depend on the numerical values of the free parameters that the function [Formula: see text] holds.

scholarly journals Generalized Phenomenological Models of Dark Energy

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Prasenjit Paul ◽  
Rikpratik Sengupta
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Phenomenological Models ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Free Parameters ◽  
The Universe ◽  
Matter Energy

It was first observed at the end of the last century that the universe is presently accelerating. Ever since, there have been several attempts to explain this observation theoretically. There are two possible approaches. The more conventional one is to modify the matter part of the Einstein field equations, and the second one is to modify the geometry part. We shall consider two phenomenological models based on the former, more conventional approach within the context of general relativity. The phenomenological models in this paper consider a Λ term firstly a function of a¨/a and secondly a function of ρ, where a and ρ are the scale factor and matter energy density, respectively. Constraining the free parameters of the models with the latest observational data gives satisfactory values of parameters as considered by us initially. Without any field theoretic interpretation, we explain the recent observations with a dynamical cosmological constant.

scholarly journals TRAPPING PHOTONS BY A LINE SINGULARITY

2003 ◽  
Vol 12 (06) ◽  
pp. 1095-1112 ◽  
Author(s):  
METIN ARIK ◽  
OZGUR DELICE
Keyword(s):  
Energy Density ◽  
Thin Shell ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Cylindrically Symmetric ◽  
Static Solutions ◽  
Line Singularity ◽  
Thick Shells

We present cylindrically symmetric, static solutions of the Einstein field equations around a line singularity such that the energy momentum tensor corresponds to infinitely thin photonic shells. Positivity of the energy density of the thin shell and the line singularity is discussed. It is also shown that thick shells containing mostly radiation are possible in a numerical solution.

scholarly journals TELEPARALLEL ENERGY–MOMENTUM DISTRIBUTION OF LEWIS–PAPAPETROU SPACETIMES

2007 ◽  
Vol 22 (06) ◽  
pp. 425-433 ◽  
Author(s):  
M. SHARIF ◽  
M. JAMIL AMIR
Keyword(s):  
Energy Density ◽  
Momentum Distribution ◽  
Gravitational Effect ◽  
External Source ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Teleparallel Theory ◽  
Axisymmetric Solutions

In this paper, we find the energy–momentum distribution of stationary axisymmetric spacetimes in the context of teleparallel theory by using Möller prescription. The metric under consideration is the generalization of the Weyl metrics called the Lewis–Papapetrou metric. The class of stationary axisymmetric solutions of the Einstein field equations has been studied by Galtsov to include the gravitational effect of an external source. Such spacetimes are also astrophysically important as they describe the exterior of a body in equilibrium. The energy density turns out to be nonvanishing and well-defined and the momentum becomes constant except along θ-direction. It is interesting to mention that the results reduce to the already available results for the Weyl metrics when we take ω = 0.

Weyl static axially symmetric field equations in modified f(T) gravity

2017 ◽  
Vol 14 (04) ◽  
pp. 1750053 ◽  
Author(s):  
Saeed Nayeh ◽  
Mehrdad Ghominejad
Keyword(s):  
General Relativity ◽  
Symmetric Space ◽  
Energy Momentum Tensor ◽  
Radial Component ◽  
Momentum Tensor ◽  
Space Time ◽  
Axially Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Torsion Scalar

In this paper, we obtain the field equations of Weyl static axially symmetric space-time in the framework of [Formula: see text] gravity, where [Formula: see text] is torsion scalar. We will see that, for [Formula: see text] related to teleparallel equivalent general relativity, these equations reduce to Einstein field equations. We show that if the components of energy–momentum tensor are symmetric, the scalar torsion must be either constant or only a function of radial component [Formula: see text]. The solutions of some functions [Formula: see text] in which [Formula: see text] is a function of [Formula: see text] are obtained.

Kaluza–Klein Cosmological Model, Strange Quark Matter, and Time-Varying Lambda

2014 ◽  
Vol 69 (1-2) ◽  
pp. 90-96 ◽  
Author(s):  
Namrata Jain ◽  
Shyamsunder S. Bhoga ◽  
Gowardhan S. Khadekar
Keyword(s):  
Cosmological Model ◽  
Quark Matter ◽  
Strange Quark ◽  
Strange Quark Matter ◽  
Time Varying ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Different Types ◽  
Free Parameters ◽  
Kaluza Klein

In this paper, exact solutions of the Einstein field equations of the Kaluza-Klein cosmological model have been obtained in the presence of strange quark matter. We have considered the timevarying cosmological constant Λ as Λ = αH2 + βR-2, where α and β are free parameters. The solutions are obtained with the help of the equation of state for strange quark matter as per the Bag model, i.e. quark pressure p = 1/3(ρ - 4BC), where BC is Bag’s constant. We also discussed the physical implications of the solutions obtained for the model for different types of universes.

scholarly journals Revisiting the Cosmological Constant Problem within Quantum Cosmology

Universe ◽  
2020 ◽  
Vol 6 (8) ◽  
pp. 108
Author(s):  
Vesselin Gueorguiev ◽  
Andre Maeder
Keyword(s):  
Energy Density ◽  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Vacuum Energy ◽  
Planck Scale ◽  
Vacuum Energy Density ◽  
Characteristic Scale ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Cosmological Constant Problem

A new perspective on the Cosmological Constant Problem (CCP) is proposed and discussed within the multiverse approach of Quantum Cosmology. It is assumed that each member of the ensemble of universes has a characteristic scale a that can be used as integration variable in the partition function. An averaged characteristic scale of the ensemble is estimated by using only members that satisfy the Einstein field equations. The averaged characteristic scale is compatible with the Planck length when considering an ensemble of solutions to the Einstein field equations with an effective cosmological constant. The multiverse ensemble is split in Planck-seed universes with vacuum energy density of order one; thus, Λ˜≈8π in Planck units and a-derivable universes. For a-derivable universe with a characteristic scale of the order of the observed Universe a≈8×1060, the cosmological constant Λ=Λ˜/a2 is in the range 10−121–10−122, which is close in magnitude to the observed value 10−123. We point out that the smallness of Λ can be viewed to be natural if its value is associated with the entropy of the Universe. This approach to the CCP reconciles the Planck-scale huge vacuum energy–density predicted by QFT considerations, as valid for Planck-seed universes, with the observed small value of the cosmological constant as relevant to an a-derivable universe as observed.

scholarly journals Cosmological test on viscous bulk models using Hubble parameter measurements and type Ia supernovae data

2019 ◽  
Vol 79 (9) ◽  
Author(s):  
A. Hernández-Almada
Keyword(s):  
Hubble Parameter ◽  
Point Of View ◽  
Type Ia Supernovae ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Type Ia ◽  
Free Parameters ◽  
Ia Supernovae ◽  
The Universe ◽  
Phenomenological Point

Abstract From a phenomenological point of view, we analyze the dynamics of the Universe at late times by introducing a polynomial and hyperbolic bulk viscosity into the Einstein field equations respectively. We constrain their free parameters using the observational Hubble parameter data and the Type Ia Supernovae dataset to reconstruct the deceleration q and the jerk j parameters within the redshift region $$0<z<2.5$$0<z<2.5. At current epochs, we obtain $$q_0 = -\,0.680^{+0.085}_{-0.102}$$q0=-0.680-0.102+0.085 and $$j_0 = 2.782^{+1.198}_{-0.741}$$j0=2.782-0.741+1.198 for the polynomial model and $$q_0 = -\,0.539^{+0.040}_{-0.038}$$q0=-0.539-0.038+0.040 ($$-\,0.594^{+0.056}_{-0.056}$$-0.594-0.056+0.056) and $$j_0 = 0.297^{+0.051}_{-0.050}$$j0=0.297-0.050+0.051 ($$1.124^{+0.196}_{-0.178}$$1.124-0.178+0.196) for the tanh (cosh) model. Furthermore, we explore the statefinder diagnostic that gives us evident differences with respect to the concordance model (LCDM). According to our results this kind of models is not supported by the data over LCDM.

Cosmic evolution in the background of R (1 + αQ) gravity

2019 ◽  
Vol 34 (31) ◽  
pp. 1950253 ◽  
Author(s):  
M. Zubair ◽  
M. Zeeshan ◽  
Saira Waheed
Keyword(s):  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Momentum Tensor ◽  
Model Parameters ◽  
Field Equations ◽  
Cosmic Evolution ◽  
Test Particles ◽  
Free Model ◽  
Free Parameters ◽  
Modified Theory

In this paper, we discuss the cosmic evolution in a modified theory involving non-minimal interaction of geometry and matter, labeled as [Formula: see text] gravity, where [Formula: see text] is the non-minimal interaction term. First, we develop the dynamical [Formula: see text] field equations for Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime and then by using divergence of these equations, we explore its interesting outcome of non-conserved energy–momentum tensor (EMT). The presence of geometry matter coupling in such theories results in non-geodesic test particles motion and hence causes an additional force orthogonal to four-velocity of these particles. By taking these interesting features into account along with a particular choice of Lagrangian [Formula: see text], we explore the resulting expression of energy density. Further, the free model parameters are constrained using energy condition bounds where it is concluded that these values of free parameters are compatible with the recent data.

scholarly journals Viscous string cosmological models in alternative theory of gravity

2017 ◽  
Vol 1 (5) ◽  
pp. 180-187
Author(s):  
Mishra RK ◽  
Chand A
Keyword(s):  
Energy Density ◽  
Cosmic Time ◽  
String Tension ◽  
Cosmological Models ◽  
Alternative Theory ◽  
Late Time ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Suitable Relation ◽  
Increasing Function

In present communication, the Bianchi type-III, viscous string cosmological models have been investigated in scalar-tensor Brans-Dicke gravity. To obtain an exact solution of the Einstein field equations (EFE), it is assumed that the viscosity is the power function of energy density and the deceleration parameter (DP) as a function of cosmic time with suitable relation i.e. a(t)=[sinh(αt)]1/n , here α,n≠0 are constants. It is observed that the power index has the important significance on the evolution of string cosmological models. It is also noticed that the string tension density (λ) is increasing function of time where as the energy density (ρ) and the cosmological constant (Λ) are decreasing with time and converges to a small value at late time. For better understanding of the model, we have also presented the kinematic and geometric properties of the models.

scholarly journals $$\varLambda $$CDM suitably embedded in f(R) with a non-minimal coupling to matter

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
María Ortiz-Baños ◽  
Mariam Bouhmadi-López ◽  
Ruth Lazkoz ◽  
Vincenzo Salzano
Keyword(s):  
Energy Density ◽  
The Other ◽  
Accelerated Expansion ◽  
Gravitational Coupling ◽  
Minimal Coupling ◽  
Modified Theory Of Gravity ◽  
Expansion Of The Universe ◽  
The One ◽  
The Universe ◽  
Modified Theory

AbstractIn this work, we further study a metric modified theory of gravity which contains a non-minimal coupling to matter, more precisely, we assume two functions of the scalar curvature, $$f_1$$ f 1 and $$f_2$$ f 2 , where the first one generalises the Hilbert–Einstein action, while the second couples to the matter Lagrangian. On the one hand, assuming a $$\varLambda $$ Λ CDM background, we calculate analytical solutions for the functions $$f_1$$ f 1 and $$f_2$$ f 2 . We consider two setups: on the first one, we fix $$f_2$$ f 2 and compute $$f_1$$ f 1 and on the second one, we fix $$f_1$$ f 1 and compute $$f_2$$ f 2 . Moreover, we do the analysis for two different energy density contents, a matter dominated universe and a general perfect fluid with a constant equation of state fuelling the universe expansion. On the other hand, we complete our study by performing a cosmographic analysis for $$f_1$$ f 1 and $$f_2$$ f 2 . We conclude that the gravitational coupling to matter can drive the accelerated expansion of the universe.

Sign in / Sign up

Export Citation Format

Share Document