scholarly journals Matter Growth in Imperfect Fluid Cosmology

Universe ◽  
2019 ◽  
Vol 5 (3) ◽  
pp. 68 ◽  
Author(s):  
Winfried Zimdahl ◽  
Hermano Velten ◽  
William Algoner
Keyword(s):  
Degrees Of Freedom ◽  
Cold Dark Matter ◽  
Energy Momentum Tensor ◽  
Growth Function ◽  
Momentum Tensor ◽  
Anisotropic Pressure ◽  
Cosmic Medium ◽  
Imperfect Fluid ◽  
The Standard Model ◽  
Space Distortion

Extensions of Einstein’s General Relativity (GR) can formally be given a GR structure in which additional geometric degrees of freedom are mapped on an effective energy-momentum tensor. The corresponding effective cosmic medium can then be modeled as an imperfect fluid within GR. The imperfect fluid structure allows us to include, on a phenomenological basis, anisotropic stresses and energy fluxes which are considered as potential signatures for deviations from the cosmological standard Λ -cold-dark-matter ( Λ CDM) model. As an example, we consider the dynamics of a scalar-tensor extension of the standard model, the e Φ Λ CDM model. We constrain the magnitudes of anisotropic pressure and energy flux with the help of redshift-space distortion (RSD) data for the matter growth function f σ 8 .

TECHNIDILATON OR HIGGS?

1993 ◽  
Vol 08 (03) ◽  
pp. 275-283 ◽  
Author(s):  
EDI HALYO
Keyword(s):  
Standard Model ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Higgs Bosons ◽  
Low Energy ◽  
Gauge Bosons ◽  
Effective Lagrangian ◽  
The Standard Model

Interactions of the technidilaton with fermions and gauge bosons are obtained by constructing a low energy effective Lagrangian and using the fact that the technidilaton couples to the trace of the energy-momentum tensor Θµµ. Technidilaton’s interactions are compared with those of the Higgs bosons of the Standard Model with one or two scalar doublets.

Gravitational collapse of interacting combination of dark matter and dark energy in the context of brane world regime

2018 ◽  
Vol 33 (23) ◽  
pp. 1850132 ◽  
Author(s):  
Hasrat Hussain Shah ◽  
Farook Rahaman
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Gravitational Collapse ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Brane World ◽  
Anisotropic Pressure ◽  
Isotropic Pressure ◽  
Polytropic Equation ◽  
De Formula

In the scenario of an optimal consideration that is, homogeneous and flat spacetime, we study the Black Hole (BH) formation from the gravitational collapse of a spherical symmetric clump of matter in the case of the specific Dark Matter (DM) model interacting with Dark Energy (DE) in the context of the brane world regime. This clump of matter constituted of DM, [Formula: see text] and DE, [Formula: see text]. In the present model, we consider anisotropic pressure in the energy–momentum tensor with a polytropic equation of state (EoS), [Formula: see text] and [Formula: see text], [Formula: see text]. Our results show that the gravitational collapse of an interacting combination of DM and DE leads to the formation of BH in the presence of brane tension. Recent work provides the generalization of isotropic pressure to an-isotropic pressure in the energy–momentum tensor for the specific interacting combination model of DM and DE in a brane world regime.

LTB geometry with tilted and nontilted congruences in f(R,T) gravity

2017 ◽  
Vol 26 (09) ◽  
pp. 1750099 ◽  
Author(s):  
Z. Yousaf ◽  
M. Zaeem-ul-Haq Bhatti ◽  
Aamna Rafaqat
Keyword(s):  
Transport Equation ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Imperfect Fluid ◽  
Dynamical Features ◽  
Dust Fluid

We investigate the role of tilted and nontilted congruence in the dynamics of dissipative Lemaître–Tolman–Bondi spacetime in [Formula: see text] gravity. We consider imperfect fluid with its congruences observed by tilted observer and dust fluid filled with LTB geometry observed by the nontilted observer. In order to elaborate the dynamical features of two congruences, we consider well-known [Formula: see text] models and develop relationships between tilted and nontilted dynamical variables. We evaluate the nonzero divergence of energy–momentum tensor for tilted congruence and transport equation for the system in [Formula: see text] gravity. We have also checked the instability regimes for nontilted congruence.

scholarly journals Stress Tensor of Free Maxwell Field in Friedmann-Robertson-Walker Universe

1970 ◽  
Vol 7 (7) ◽  
pp. 1-2 ◽  
Author(s):  
SK Sharma ◽  
PR Dhungel ◽  
U Khanal
Keyword(s):  
Energy Density ◽  
Key Words ◽  
Stress Tensor ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Anisotropic Pressure ◽  
Translational Energy ◽  
Closed Universe ◽  
Scientific World ◽  
Friedmann Robertson Walker

The solutions of the Maxwellian field in FRW spacetime, found by using the Newman Penrose formalism, is used to determine the energy-momentum tensor. The tensor is obviously traceless, with the energy density equal to the sum of the radial and the two tangential pressures. But it turns out that the radial and tangential pressures are not equal, giving rise to anisotropy. Such anisotropy can be the origin of the rotation of galaxies. Another result is that the photon energy in a closed universe are quantized in units of one from the lowest value of two upwards. The lowest quantum of two can be interpreted as one unit of spin energy and one of translational energy. Key words: Galactic structure; Maxwellian field; Anisotropic pressure. DOI: 10.3126/sw.v7i7.3814 Scientific World Vol.7(7) 2009 pp.1-2

scholarly journals DARK MATTER WITH VARIABLE MASSES

1993 ◽  
Vol 02 (01) ◽  
pp. 85-95 ◽  
Author(s):  
JUAN GARCÍA-BELLIDO
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Spiral Galaxies ◽  
Energy Momentum Tensor ◽  
Gauge Coupling ◽  
Momentum Tensor ◽  
Primordial Nucleosynthesis ◽  
Effective Theories ◽  
Dilaton Coupling

String effective theories contain a dilaton scalar field which couples to gravity, matter and radiation. In general, particle masses will have different dilaton couplings. We can always choose a conformal frame in which baryons have constant masses while (nonbaryonic) dark matter have variable masses, in the context of a scalar-tensor gravity theory. We are interested in the phenomenology of this scenario. Dark matter with variable masses could have a measurable effect on the dynamical motion of the halo of spiral galaxies, which may affect cold dark matter models of galaxy formation. As a consequence of variable masses, the energy-momentum tensor is not conserved; there is a dissipative effect, due to the dilaton coupling, associated with a “dark entropy” production. In particular, if axions had variable masses they could be diluted away, thus opening the “axion window.” Assuming that dark matter with variable masses dominates the cosmological evolution during the matter era, it will affect the primordial nucleosynthesis predictions on the abundances of light elements. Furthermore, the dilaton also couples to radiation in the form of a variable gauge coupling. Experimental bounds will constrain the parameters of this model.

scholarly journals General approach to the Lagrangian ambiguity in f(R, T) gravity

2021 ◽  
Vol 81 (2) ◽  
Author(s):  
G. A. Carvalho ◽  
F. Rocha ◽  
H. O. Oliveira ◽  
R. V. Lobato
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Modified Theories Of Gravity ◽  
Energy Tensor ◽  
Field Equations ◽  
Unknown Variable ◽  
Stress Energy ◽  
The Standard Model ◽  
Theories Of Gravity ◽  
Matter Fields

AbstractThe f(R, T) gravity is a theory whose gravitational action depends arbitrarily on the Ricci scalar, R, and the trace of the stress–energy tensor, T; its field equations also depend on matter Lagrangian, $$\mathscr {L}_{m}$$ L m . In the modified theories of gravity where field equations depend on Lagrangian, there is no uniqueness on the Lagrangian definition and the dynamics of the gravitational and matter fields can be different depending on the choice performed. In this work, we have eliminated the $$\mathscr {L}_{m}$$ L m dependence from f(R, T) gravity field equations by generalizing the approach of Moraes in Ref. [1]. We also propose a general approach where we argue that the trace of the energy–momentum tensor must be considered an “unknown” variable of the field equations. The trace can only depend on fundamental constants and few inputs from the standard model. Our proposal resolves two limitations: first the energy–momentum tensor of the f(R, T) gravity is not the perfect fluid one; second, the Lagrangian is not well-defined. As a test of our approach we applied it to the study of the matter era in cosmology, and the theory can successfully describe a transition between a decelerated Universe to an accelerated one without the need for dark energy.

scholarly journals Study on Anisotropic Strange Stars in f(T,T) Gravity

2020 ◽  
Author(s):  
Ines G. Salako ◽  
M. Khlopov ◽  
Saibal Ray ◽  
M.Z. Arouko ◽  
Pameli Saha ◽  
...  
Keyword(s):  
Energy Momentum Tensor ◽  
Torsion Tensor ◽  
Equations Of Motion ◽  
Momentum Tensor ◽  
Compact Objects ◽  
Strange Star ◽  
Energy Conditions ◽  
Anisotropic Pressure ◽  
Spacetime Geometry ◽  
Physical Features

In this work, we study the existence of strange star in the background of f(T,T) gravity in the Einstein spacetime geometry, where T is the torsion tensor and T is the trace of the energy-momentum tensor. The equations of motion are derived for anisotropic pressure within the spherically symmetric strange star. We explore the physical features like energy conditions, mass-radius relations, modified TOV equations, principal of causality, adiabatic index, redshift and stability analysis of our model. These features are realistic and appealing to further investigation of properties of compact objects in f(T,T) gravity as well as their observational signatures.

Helicity decomposition of metric perturbations

2018 ◽  
Author(s):  
Michele Maggiore
Keyword(s):  
Degrees Of Freedom ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Invariant Metric ◽  
Gauge Invariant ◽  
Tensor Perturbations

Decomposition of the perturbations over FRW into scalar, vector and tensor perturbations. Physical and unphysical degrees of freedom. Gauge-invariant metric perturbations, Bardeen variables. Gauge-invariant perturbations of the energy-momentum tensor

scholarly journals On a Possibility of the Gravitational Wave Detection at the High Energy Colliders

2018 ◽  
Vol 46 ◽  
pp. 1860059
Author(s):  
Murli Manohar Verma
Keyword(s):  
Gravitational Wave ◽  
Energy Momentum Tensor ◽  
Hadron Collider ◽  
High Energy ◽  
Momentum Tensor ◽  
Missing Energy ◽  
Wave Detection ◽  
The Standard Model ◽  
Previous Proposal

A strong follow up of a previous proposal (ICHEP, Valencia 2014) is made leading to the first experiment to observe the gravitational waves at the collision sites at the colliders such as the Large Hadron Collider at CERN. The amplitudes have been calculated with regard to the sensitivity of the detector. Compared with the standard model physics, it is shown to have a measurable impact on the particle motions and corresponds to ‘missing’ energy in form of the gravitational wave loss. This is unlike the cosmological detectors like BICEP2 etc. where the indirect B mode polarization on CMBR were masked by dust. In contrast, this experiment would be the first experiment where the energy-momentum tensor of the source can be controlled.

scholarly journals Study on Anisotropic Strange Stars in f ( T , T ) Gravity

Universe ◽  
2020 ◽  
Vol 6 (10) ◽  
pp. 167
Author(s):  
Ines G. Salako ◽  
M. Khlopov ◽  
Saibal Ray ◽  
M. Z. Arouko ◽  
Pameli Saha ◽  
...  
Keyword(s):  
Energy Momentum Tensor ◽  
Torsion Tensor ◽  
Equations Of Motion ◽  
Momentum Tensor ◽  
Compact Objects ◽  
Energy Conditions ◽  
Anisotropic Pressure ◽  
Strange Stars ◽  
Spacetime Geometry ◽  
Physical Features

In this work, we study the existence of strange stars in the background of f(T,T) gravity in the Einstein spacetime geometry, where T is the torsion tensor and T is the trace of the energy-momentum tensor. The equations of motion are derived for anisotropic pressure within the spherically symmetric strange star. We explore the physical features like energy conditions, mass-radius relations, modified Tolman–Oppenheimer–Volkoff (TOV) equations, principal of causality, adiabatic index, redshift and stability analysis of our model. These features are realistic and appealing to further investigation of properties of compact objects in f(T,T) gravity as well as their observational signatures.

Sign in / Sign up

Export Citation Format

Share Document