scholarly journals Einstein-Cartan gravity with scalar-fermion interactions

Open Physics ◽  
2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Olga Razina ◽  
Yerlan Myrzakulov ◽  
Nurzhan Serikbayev ◽  
Gulgasyl Nugmanova ◽  
Ratbay Myrzakulov
Keyword(s):  
Exact Analytical Solution ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Fermionic Field ◽  
Dirac Equations ◽  
Λcdm Model ◽  
Equation Of State Parameter ◽  
Expansion Of The Universe ◽  
Cartan Theory ◽  
The Universe

AbstractIn this paper, we have considered the g-essence and its particular cases, k-essence and f-essence, within the framework of the Einstein-Cartan theory. We have shown that a single fermionic field can give rise to the accelerated expansion within the Einstein-Cartan theory. The exact analytical solution of the Einstein-Cartan-Dirac equations is found. This solution describes the accelerated expansion of the Universe with the equation of state parameter w = −1 as in the case of ΛCDM model.

scholarly journals R+RG gravity with maximal Noether symmetry

2021 ◽  
Vol 2081 (1) ◽  
pp. 012028
Author(s):  
Yu E Pokrovsky
Keyword(s):  
Dimensional Space ◽  
Accelerated Expansion ◽  
Acoustic Oscillations ◽  
Riemann Curvature Tensor ◽  
Metric Tensor ◽  
Λcdm Model ◽  
Dimensional Space Time ◽  
Expansion Of The Universe ◽  
Alpha Beta ◽  
The Universe

Abstract A Noether symmetric, 3rd order polynomial in the Riemann curvature tensor R αβμν extension of the General Relativity (GR) without cosmological constant (R+RG gravity) is suggested and discussed as a possible fundamental theory of gravity in 4-dimensional space-time with the geometric part of the Lagrangian to be L R + R G = − g 2 k R ( 1 + G G P ) . Here k = 8 π G N c 4 is the Einstein constant, g = det ( g μ ν ) , g μ ν - the metric tensor, GN - the Newton constant, c - the speed of light, R = R μ ν μ ν - the Ricci scalar, G = R 2 − 4 R μ ν R μ ν + R α β μ ν R α β μ ν - the Gauss-Bonnet topological invariant, and GP - a new constant of the gravitational self-interaction to model the cosmological bounce, inflation, accelerated expansion of the Universe, etc. The best fit to the Baryon Acoustic Oscillations data for the Hubble parameter H (z) at the redshifts z<2.36 leads to G P 1 / 4 = ( 0.557 ± 0.014 ) T p c − 1 with the mean square weighted deviation from the data about 3 times smaller than for the standard cosmological (ΛCDM) model. Due to the self-gravitating term ∼RG the respective Einstein equation in the R+RG gravity contains the additional (tachyonic in the past and now) scalar (spin = 0) graviton and the perfect geometric fluid tensor with pressure-and matter-like terms equal to the respective terms in the ΛCDM model at |z| 1. Some predictions of this R+RG gravity for the Universe are also done.

scholarly journals Dynamical Properties of Dark Energy Models in Fractal Universe

Symmetry ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1174
Author(s):  
Muhammad Umair Shahzad ◽  
Ayesha Iqbal ◽  
Abdul Jawad
Keyword(s):  
Dark Energy ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Accelerating Universe ◽  
Statefinder Parameters ◽  
Om Diagnostic ◽  
Energy Models ◽  
Expansion Of The Universe ◽  
Dynamical Properties ◽  
The Universe

In this paper, we consider the flat FRW spacetime filled with interacting dark energy and dark matter in fractal universe. We work with the three models of dark energy named as Tsallis, Renyi and Sharma–Mittal. We investigate different cosmological implications such as equation of state parameter, squared speed of sound, deceleration parameter, statefinder parameters, ω e f f - ω e f f ´ (where prime indicates the derivative with respect to ln a , and a is cosmic scale factor) plane and Om diagnostic. We explore these parameters graphically to study the evolving universe. We compare the consistency of dark energy models with the accelerating universe observational data. All three models are stable in fractal universe and support accelerated expansion of the universe.

scholarly journals Barrow HDE model for statefinder diagnostic in FLRW universe

2021 ◽  
pp. 2150030
Author(s):  
Anirudh Pradhan ◽  
Archana Dixit ◽  
Vinod Kumar Bhardwaj
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Density Parameter ◽  
Phantom Divide ◽  
Phantom Divide Line ◽  
Expansion Of The Universe ◽  
Flrw Universe ◽  
The Universe

We have analyzed the Barrow holographic dark energy (BHDE) in the framework of flat FLRW universe by considering the various estimations of Barrow exponent △. Here, we define BHDE, by applying the usual holographic principle at a cosmological system, for utilizing the Barrow entropy rather than the standard Bekenstein–Hawking. To understand the recent accelerated expansion of the universe, consider the Hubble horizon as the IR cutoff. The cosmological parameters, especially the density parameter [Formula: see text], the equation of the state parameter [Formula: see text], energy density [Formula: see text] and the deceleration parameter [Formula: see text] are studied in this paper and found the satisfactory behaviors. Moreover we additionally focus on the two geometric diagnostics, the statefinder [Formula: see text] and [Formula: see text] to discriminant BHDE model from the [Formula: see text]CDM model. Here we determined and plotted the trajectories of evolution for statefinder [Formula: see text], [Formula: see text] and [Formula: see text] diagnostic plane to understand the geometrical behavior of the BHDE model by utilizing Planck 2018 observational information. Finally, we have explored the new Barrow exponent △, which strongly affects the dark energy equation of state that can lead it to lie in the quintessence regime, phantom regime and exhibits the phantom-divide line during the cosmological evolution.

scholarly journals Noether symmetry approach in f (T, B) teleparallel gravity with a fermionic field

2021 ◽  
Vol 2090 (1) ◽  
pp. 012058
Author(s):  
Yerlan Myrzakulov ◽  
Sabit Bekov ◽  
Kairat Myrzakulov
Keyword(s):  
Cosmological Model ◽  
Teleparallel Gravity ◽  
Noether Symmetry ◽  
Accelerated Expansion ◽  
Late Time ◽  
Fermionic Field ◽  
Symmetry Approach ◽  
Expansion Of The Universe ◽  
Isotropic Cosmological Model ◽  
The Universe

Abstract In this work, we consider a homogeneous and isotropic cosmological model of the universe in f (T, B) gravity with non-minimally coupled fermionic field. In order to find the form of the coupling function F(Ψ), the potential function V (Ψ) of the fermionic field and the function f (T, B), we found through the Noether symmetry approach. The results obtain are coincide with the observational data that describe the late-time accelerated expansion of the universe.

A reconstruction scheme for f(T) gravity and its consequences in the perturbation level

2018 ◽  
Vol 15 (02) ◽  
pp. 1850025 ◽  
Author(s):  
Surajit Chattopadhyay
Keyword(s):  
Equation Of State ◽  
Power Law ◽  
State Parameter ◽  
Reconstruction Scheme ◽  
Equation Of State Parameter ◽  
Expansion Of The Universe ◽  
Text Model ◽  
The Universe ◽  
Reconstructed Model ◽  
Metric Fluctuations

The present study reports a reconstruction scheme for [Formula: see text] gravity considering the scale factor in the power law form. The equation of state parameter has been studied for this reconstructed model along with the deceleration parameter and the statefinder pair [Formula: see text]. The statefinder trajectory has been found to interpolate between dust and [Formula: see text]CDM phase of the universe. Cosmological evolution of primordial perturbations has been studied through scalar metric fluctuations and finally the reconstructed [Formula: see text] model has been tested for its consistency with the generic expansion of the universe.

scholarly journals Quantum Space and the Evolution of the Dark Universe

2017 ◽  
Author(s):  
Carlos A. Melendres
Keyword(s):  
Phase Diagram ◽  
Dark Matter ◽  
Dark Energy ◽  
State Parameter ◽  
Big Bang ◽  
Accelerated Expansion ◽  
Quantum Space ◽  
Fundamental Particles ◽  
Expansion Of The Universe ◽  
The Universe

We present a model of space that considers it to be a quantized dynamical entity which is a component of the universe along with matter and radiation. The theory is used together with&nbsp; thermodynamic data&nbsp; to provide a new view of cosmic&nbsp; evolution&nbsp; and an insight into the nature of dark energy and dark matter. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Space is made up of energy quanta. The universe started from an atomic size volume at very high&nbsp; temperature and pressure near the Planck epoch. Upon expansion &nbsp;and&nbsp; cooling, phase transitions occurred&nbsp; resulting in the formation of radiation,&nbsp; fundamental particles, and matter. These&nbsp; nucleate and grow into stars, galaxies, and clusters. From a phase diagram of cosmic&nbsp; composition,&nbsp; we&nbsp; obtained&nbsp; a correlation between&nbsp;&nbsp; dark energy&nbsp; and the energy of space. Using&nbsp; the Friedmann&nbsp; equations, data from WMAP studies of&nbsp; the composition of the universe&nbsp; at 3.0 x 105 (a=5.25 x 10-2) years&nbsp; and at present (a=1), are well fitted by our&nbsp; model with an equation of state parameter, w= -0.7.&nbsp; The accelerated expansion of the universe, starting at about 7&nbsp; billion years, determined by&nbsp; BOSS measurements,&nbsp; also correlates well with the dominance of dark energy&nbsp; at 7.25 x 109 years ( a= 0.65). The expansion&nbsp; can be&nbsp; attributed to Quintessence with a &nbsp;space force &nbsp;arising from a quantum space field.&nbsp; From our phase diagram, we also find a correlation suggesting&nbsp; that&nbsp; dark matter is a plasma form of matter similar to that&nbsp; which existed during the photon epoch&nbsp; immediately prior to recombination. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Our Quantum Space&nbsp; Model leads to a&nbsp; universe which&nbsp; is &nbsp;homogeneous and isotropic without the need for inflation. The thermodynamics of expansion is consistent with &nbsp;BOSS data &nbsp;that &nbsp;show the process &nbsp;to be &nbsp;adiabatic and the rate of expansion &nbsp;decelerating &nbsp;during &nbsp;the first&nbsp; 6 &nbsp;billion years after the Big Bang. &nbsp;However, it &nbsp;became non-adiabatic and accelerating thereafter. This &nbsp;implies &nbsp;an influx &nbsp;of energy from a source outside the universe; it warrants consideration as a possible factor &nbsp;in &nbsp;the accelerated expansion of the universe. &nbsp;

scholarly journals Constraining effective equation of state in f(Q, T) gravity

2021 ◽  
Vol 81 (6) ◽  
Author(s):  
Simran Arora ◽  
Abhishek Parida ◽  
P. K. Sahoo
Keyword(s):  
Equation Of State ◽  
State Parameter ◽  
Momentum Tensor ◽  
Accelerated Expansion ◽  
Dark Sector ◽  
Effective Equation ◽  
Best Fitting ◽  
Expansion Of The Universe ◽  
Two Parameters ◽  
The Universe

AbstractNew high-precision observations are now possible to constrain different gravity theories. To examine the accelerated expansion of the Universe, we used the newly proposed f(Q, T) gravity, where Q is the non-metricity, and T is the trace of the energy–momentum tensor. The investigation is carried out using a parameterized effective equation of state with two parameters, m and n. We have also considered the linear form of $$f(Q,T)= Q+bT$$ f ( Q , T ) = Q + b T , where b is constant. By constraining the model with the recently published 1048 Pantheon sample, we were able to find the best fitting values for the parameters b, m, and n. The model appears to be in good agreement with the observations. Finally, we analyzed the behavior of the deceleration parameter and equation of state parameter. The results support the feasibility of f(Q, T) as a promising theory of gravity, illuminating a new direction towards explaining the Universe dark sector.

Study of Tsallis, Rényi and Sharma–Mittal holographic dark energies for entropy corrected modified field equations in Hořava–Lifshitz gravity

2020 ◽  
Vol 17 (11) ◽  
pp. 2050170
Author(s):  
Sayani Maity ◽  
Ujjal Debnath
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Speed Of Sound ◽  
Cold Dark Matter ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Field Equations ◽  
Frw Universe ◽  
Equation Of State Parameter ◽  
The Universe

The purpose of this work is to study the Tsallis, Rényi and Sharma–Mittal holographic dark energy models in order to evaluate the accelerated expansion of the Universe. In this regard, we consider the modified field equations for logarithmic and power law versions of entropy corrected models in FRW Universe filled with interacting dark energy and cold dark matter within the framework of Hořava–Lifshitz gravity. Employing the Nojiri and Odintsov (NO) cut-off as infrared cutoff, we explore the nature of the different cosmological quantities like the equation of state parameter, squared speed of sound and [Formula: see text]–[Formula: see text] cosmological plane during the cosmic evolution. The equation of state parameter shows the different stages of the evolution of the Universe for the considered models. By analyzing the cosmological plane [Formula: see text]–[Formula: see text], we obtain the freezing region for these models. Also, due to the study of squared speed of sound, we show the classically stable behavior of the considered models.

scholarly journals Cosmic Consequences of Kaniadakis and Generalized Tsallis Holographic Dark Energy Models in the Fractal Universe

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Abdul Jawad ◽  
Abdul Malik Sultan
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Apparent Horizon ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Energy Models ◽  
Expansion Of The Universe ◽  
The Stability ◽  
The Universe

We investigate the recently proposed holographic dark energy models with the apparent horizon as the IR cutoff by assuming Kaniadakis and generalized Tsallis entropies in the fractal universe. The implications of these models are discussed for both the interacting ( Γ = 3 H b 2 ρ m ) and noninteracting ( b 2 = 0 ) cases through different cosmological parameters. Accelerated expansion of the universe is justified for both models through deceleration parameter q . In this way, the equation of state parameter ω d describes the phantom and quintessence phases of the universe. However, the coincidence parameter r ~ = Ω m / Ω d shows the dark energy- and dark matter-dominated eras for different values of parameters. It is also mentioned here that the squared speed of sound gives the stability of the model except for the interacting case of the generalized Tsallis holographic dark energy model. It is mentioned here that the current dark energy models at the apparent horizon give consistent results with recent observations.

scholarly journals Quantum Space and Dark Energy

2017 ◽  
Author(s):  
Carlos A. Melendres
Keyword(s):  
Dark Energy ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Fundamental Particles ◽  
Wave Particle Duality ◽  
Expansion Of The Universe ◽  
Cooling Phase ◽  
Temperature And Pressure ◽  
The Universe ◽  
Very High

The accelerated expansion of the universe is of great scientific interest. It is attributed to Dark Energy. We present a quantum theory of space，and a thermodynamic approach to modeling the evolution of the universe, that explain it. Space is a dynamical entity made up of energy quanta. From wave particle duality, they can also be considered as a gas. The universe evolved starting from a point size volume of gas at very high temperature and pressure. Upon expansion and cooling, phase transitions occured resulting in the formation of fundamental particles, radiation, and matter; these nucleate and grow into stars, galaxies, and clusters. From a phase diagram of cosmic composition , we obtained a correlation between dark energy and the energy of space. A repulsive space force causes the expansion of the universe; the space quanta arise from a space field. Using the Friedmann equations， data on the composition of the universe at 3.0 x 105 (a=5.25 x 10&minus;2) years and at present (a=l), obtained from WMAP studies, are well fitted by our model with an equation of state parameter, w= &minus;0.7. The accelerated expansion of the universe, starting at about 7 billion years, determined by BOSS measurements, correlates well with the dominance of dark energy at 7.25 x 109 years ( a= 0.65). The expansion is attributed to Quintessence.

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