LRS Bianchi-I transit universe with periodic varying q in f(R,T) gravity

2019 ◽  
Vol 16 (12) ◽  
pp. 1950195
Author(s):  
Vinod Kumar Bhardwaj ◽  
Manoj Kumar Rana
Keyword(s):  
Functional Form ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Oscillatory Behavior ◽  
Eos Parameter ◽  
Bianchi I ◽  
Accelerating Expansion ◽  
Wide Range ◽  
Transit Universe ◽  
Modified Formula

We have investigated the cosmic transit behavior of LRS Bianchi-I universe in modified [Formula: see text] gravity theory whose functional form is taken as [Formula: see text], where [Formula: see text] is Ricci scalar and [Formula: see text] is the energy–momentum tensor. Subjecting the deceleration parameter [Formula: see text] to periodic variations as [Formula: see text], where [Formula: see text], the oscillatory behavior of EoS parameter and violation of energy–momentum conservation in the wide range of parameters have been observed. Hubble parameter oscillates but remains positive which signify the alternate decelerating and accelerating expansion of universe with no singularity.

scholarly journals A periodic varying deceleration parameter in f(R, T) gravity

2018 ◽  
Vol 33 (33) ◽  
pp. 1850193 ◽  
Author(s):  
P. K. Sahoo ◽  
S. K. Tripathy ◽  
Parbati Sahoo
Keyword(s):  
Deceleration Parameter ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Oscillatory Behavior ◽  
Matter Content ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Field Equations ◽  
Eos Parameter ◽  
Wide Range

The phenomenon of accelerated expansion of the present universe and a cosmic transit aspect is explored in the framework of a modified gravity theory known as f(R, T) gravity (where R is the Ricci scalar and T is the trace of the energy–momentum tensor of the matter content). The cosmic transit phenomenon signifies a signature flipping behavior of the deceleration parameter. We employ a periodic varying deceleration parameter and obtained the exact solution of field equations. The dynamical features of the model including the oscillatory behavior of the EOS parameter are studied. We have also explored the obvious violation of energy–momentum conservation in f(R, T) gravity. The periodic behavior of energy conditions for the model are also discussed with a wide range of the free parameters.

FRW cosmological models with cosmological constant in f (R,T) theory of gravity

2021 ◽  
Author(s):  
Anirudh Pradhan ◽  
Priyanka Garg ◽  
Archana Dixit
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Apparent Magnitude ◽  
Physical Parameters ◽  
Distance Modulus ◽  
Luminosity Distance ◽  
Field Equations ◽  
Eos Parameter ◽  
Accelerating Expansion ◽  
Frw Cosmological Model

In the present paper, we have generalized the behaviors of {\color{blue}transit-decelerating to accelerating} FRW cosmological model in f (R, T) gravity theory, where R, T are Ricci scalar and trace of energy-momentum tensor respectively. The solution of the corresponding field equations is obtained by assuming a linear function of the Hubble parameter H, i.e., q = c<sub>1</sub> + c<sub>2</sub>H which gives a time-dependent DP (deceleration parameter) q(t)=-1+\frac{c_2}{\sqrt{2c_2 t +c_3}}, where c<sub>3</sub> and c<sub>2</sub> are arbitrary integrating constants [Tiwari et al., Eur. Phys. J. Plus: 131, 447 (2016); 132, 126 (2017)]. There are two scenarios in which we explain the particular form of scale factor thus obtained  (i) By using the recent constraints from OHD and JLA data which shows a cosmic deceleration to acceleration and (ii) By using new constraints from supernovae type la union data which shows accelerating expansion universe (q<0) throughout the evolution. We have observed that the EoS parameter, energy density parameters, and important cosmological planes yield the results compatible with the modern observational data. For the derived models, we have calculated various physical parameters as Luminosity distance, Distance modulus, and Apparent magnitude versus redshift for both supporting current observations.

Relativistic charged sphere in f(G,T) gravity

2021 ◽  
pp. 2150152
Author(s):  
M. Ilyas ◽  
A. R. Athar ◽  
Bilal Masud
Keyword(s):  
Observational Data ◽  
Density Profile ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Low Energy ◽  
Charged Sphere ◽  
Energy Limit ◽  
Modified Formula ◽  
Superstring Theories ◽  
Charged Spheres

This study explores the interior geometry of static relativistic charged spheres in the background of a recently proposed modified [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] are the Gauss–Bonnet (GB) invariant and trace of energy–momentum tensor, respectively. The GB gravity is the low-energy limit of superstring theories. The structures of specific relativistic charged spheres Vela [Formula: see text], [Formula: see text], and [Formula: see text] are studied in this theory of gravity. We analyzed several physical behaviors of these relativistic charged spheres with the help of observational data and investigated the various aspects like density profile, stresses, the distribution of charges, stability, etc.

scholarly journals New cosmological solutions in hybrid metric-Palatini gravity from dynamical symmetries

2021 ◽  
pp. 2150100
Author(s):  
Andronikos Paliathanasis
Keyword(s):  
Conservation Laws ◽  
Integrable Systems ◽  
Functional Form ◽  
Analytic Solutions ◽  
Momentum Conservation ◽  
Field Equations ◽  
Dynamical Symmetries ◽  
Cosmological Solutions ◽  
Liouville Integrable

We investigate the existence of Liouville integrable cosmological models in hybrid metric-Palatini theory. Specifically, we use the symmetry conditions for the existence of quadratic in the momentum conservation laws for the field equations as constraint conditions for the determination of the unknown functional form of the theory. The exact and analytic solutions of the integrable systems found in this study are presented in terms of quadratics and Laurent expansions.

scholarly journals Spin Polarized Transport in an AC-Driven Quantum Curved Nanowire

2011 ◽  
Vol 2011 ◽  
pp. 1-5 ◽  
Author(s):  
Walid A. Zein ◽  
Nabil A. Ibrahim ◽  
Adel H. Phillips
Keyword(s):  
Spin Polarization ◽  
Small Strain ◽  
Oscillatory Behavior ◽  
Tunneling Magnetoresistance ◽  
Mass Approximation ◽  
Wide Range ◽  
Spin Polarized ◽  
Polarized Transport ◽  
The One ◽  
Spin Polarized Transport

Using the effective-mass approximation method, and Floquet theory, we study the spin transport characteristics through a curved quantum nanowire. The spin polarization, P, and the tunneling magnetoresistance, TMR, are deduced under the effect of microwave and infrared radiations of wide range of frequencies. The results show an oscillatory behavior of both the spin polarization and the tunneling magnetoresistance. This is due to Fano-type resonance and the interplay between the strength of spin-orbit coupling and the photons in the subbands of the one-dimensional nanowire. The present results show that this investigation is very important, and the present device might be used to be a sensor for small strain in semiconductor nanostructures and photodetector.

scholarly journals Some exact solutions in f(𝒢,T) gravity via Noether symmetries

2017 ◽  
Vol 32 (16) ◽  
pp. 1750086 ◽  
Author(s):  
M. Farasat Shamir ◽  
Mushtaq Ahmad
Keyword(s):  
Exact Solutions ◽  
Momentum Tensor ◽  
Gravity Models ◽  
Noether Symmetry ◽  
Type I ◽  
Conserved Quantities ◽  
Rotationally Symmetric ◽  
Bianchi Type I Universe ◽  
Modified Formula ◽  
Bonnet Term

This paper is devoted to investigate the recently proposed modified Gauss–Bonnet [Formula: see text] gravity, with [Formula: see text], the Gauss–Bonnet term, coupled with [Formula: see text], the trace of energy–momentum tensor. We have used the Noether symmetry methodology to discuss some cosmologically important [Formula: see text] gravity models with anisotropic background. In particular, the Noether symmetry equations for modified [Formula: see text] gravity are reported for locally rotationally symmetric Bianchi type I universe. Explicitly, two models have been proposed to explore the exact solutions and the conserved quantities. It is concluded that the specific models of modified Gauss–Bonnet gravity may be used to reconstruct [Formula: see text]CDM cosmology without involving any cosmological constant.

scholarly journals Rip cosmologies, wormhole solutions and big trip in the f(T,𝒯 ) theory of gravity

2020 ◽  
Vol 17 (08) ◽  
pp. 2050116 ◽  
Author(s):  
Maxime Z. Arouko ◽  
Ines G. Salako ◽  
A. D. Kanfon ◽  
M. J. S. Houndjo ◽  
Etienne Baffou
Keyword(s):  
Energy Momentum Tensor ◽  
Late Phase ◽  
Momentum Tensor ◽  
Cosmological Models ◽  
The Other ◽  
Throat Radius ◽  
Eos Parameter ◽  
Wormhole Throat ◽  
Initial Epoch ◽  
Theory Of Gravity

Rip cosmological models have been investigated in the framework of [Formula: see text] theory of gravity, where [Formula: see text] denotes the torsion and [Formula: see text] is the trace of the energy–momentum tensor. These phantom cosmological models revealed that at initial epoch a EoS parameter [Formula: see text] tends asymptotically at late phase to [Formula: see text] [Formula: see text]. On the other hand, Wormhole Solutions and Big Trip have been subject to an investigation. The wormhole throat radius [Formula: see text] and the conditions to be satisfied to produce the Big Trip phenomenon have been discussed.

scholarly journals Hints of modified gravity in cosmos and in the lab?

2019 ◽  
Vol 28 (05) ◽  
pp. 1942001 ◽  
Author(s):  
Leandros Perivolaropoulos ◽  
Lavrentios Kazantzidis
Keyword(s):  
Growth Rate ◽  
Modified Gravity ◽  
Gravitational Theory ◽  
Fine Tuning ◽  
Cosmological Perturbations ◽  
Accelerating Expansion ◽  
Wide Range ◽  
Expansion Of The Universe ◽  
Gravity Theories ◽  
Parameter Values

General Relativity (GR) is consistent with a wide range of experiments/observations from millimeter scales up to galactic scales and beyond. However, there are reasons to believe that GR may need to be modified because it includes singularities (it is an incomplete theory) and also it requires fine-tuning to explain the accelerating expansion of the universe through the cosmological constant. Therefore, it is important to check various experiments and observations beyond the above range of scales for possible hints of deviations from the predictions of GR. If such hints are found it is important to understand which classes of modified gravity theories are consistent with them. The goal of this review is to summarize recent progress on these issues. On sub-millimeter scales, we show an analysis of the data of the Washington experiment [D. J. Kapner, T. S. Cook, E. G. Adelberger, J. H. Gundlach, B. R. Heckel, C. D. Hoyle and H. E. Swanson, Phys. Rev. Lett. 98 (2007) 021101, arXiv:hep-ph/0611184 [hep-ph]] searching for modifications of Newton’s Law on sub-millimeter scales and demonstrate that a spatially oscillating signal is hidden in this dataset. We demonstrate that even though this signal cannot be explained in the context of standard modified theories (viable scalar tensor and [Formula: see text] theories), it is a rather generic prediction of nonlocal gravity theories. On cosmological scales we review recent analyses of Redshift Space Distortion (RSD) data which measure the growth rate of cosmological perturbations at various redshifts and show that these data are in some tension with the [Formula: see text]CDM parameter values indicated by Planck/2015 CMB data at about [Formula: see text] level. This tension can be reduced by allowing for an evolution of the effective Newton constant that determines the growth rate of cosmological perturbations. We conclude that even though this tension between the data and the predictions of GR could be due to systematic/statistical uncertainties of the data, it could also constitute early hints pointing towards a new gravitational theory.

scholarly journals Tomography-based determination of permeability and Dupuit–Forchheimer coefficient of characteristic snow samples

2011 ◽  
Vol 57 (205) ◽  
pp. 811-816 ◽  
Author(s):  
Emilie Zermatten ◽  
Sophia Haussener ◽  
Martin Schneebeli ◽  
Aldo Steinfeld
Keyword(s):  
Mass Transport ◽  
Effective Properties ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Momentum Conservation ◽  
Micro Computed Tomography ◽  
Wide Range ◽  
Snow Microstructure ◽  
Semi Empirical

AbstractA tomography-based methodology for the mass transport characterization of snow is presented. Five samples, characteristic for a wide range of seasonal snow, are considered. Their three-dimensional (3-D) geometrical representations are obtained by micro-computed tomography and used in direct pore-level simulations to numerically solve the governing mass and momentum conservation equations, allowing for the determination of their effective permeability and Dupuit–Forchheimer coefficient. The extension to the Dupuit–coefficient is useful near the snow surface, where Reynolds numbers higher than unity can appear. Simplified semi-empirical models of porous media are also examined. The methodology presented allows for the determination of snow’s effective mass transport properties, which are strongly dependent on the snow microstructure and morphology. These effective properties can, in turn, readily be used in snowpack volume-averaged (continuum) models such as strongly layered samples with macroscopically anisotropic properties.

THE FUZZY BAG MODEL REVISITED

2002 ◽  
Vol 17 (09) ◽  
pp. 543-553 ◽  
Author(s):  
F. PILOTTO ◽  
C. A. Z. VASCONCELLOS ◽  
H. T. COELHO
Keyword(s):  
Functional Form ◽  
Potential Model ◽  
Center Of Mass ◽  
Momentum Conservation ◽  
Radial Dependence ◽  
Bag Model ◽  
New Feature ◽  
The Masses ◽  
Relativistic Potential ◽  
Energy Momentum Conservation

In this work we develop a new version of the fuzzy bag model. The new feature is the inclusion of energy–momentum conservation. This turns the model into a "real" bag model, as opposed to a relativistic potential model. One immediate consequence is that the bag constant B will acquire a radial dependence, B = B(r), whose functional form can be completely fixed without any arbitrariness. Such a feature is of importance in the study of neutron stars, where a radial dependence of B is usually put in by hand. The parameters of the model are found by fitting the masses of the baryon octet. We include center-of-mass, one-gluon exchange and pion exchange corrections for these masses.

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