Accelerated expansion of the Universe in a higher dimensional modified gravity with Euler-Poincaré terms

In this work, we reconstruct the f(R) modified gravity for different ghost and generalized-ghost dark energy (DE) models in FRW flat universe, which describes the accelerated expansion of the universe. The equation of state and deceleration parameter of reconstructed f(R) gravity have been calculated. The equation of state and deceleration parameter of reconstructed f(R)-ghost/generalized-ghost DE, have been calculated. We show that the corresponding f(R) gravity of ghost/generalized-ghost DE model can behave like phantom or quintessence. Also the transition between deceleration to acceleration regime is indicated by deceleration parameter diagram for reconstructed f(R) generalized-ghost DE model.

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REINVENTING SPACETIME ON A DYNAMICAL HYPERSURFACE

Modern Physics Letters A ◽

10.1142/s0217732306020214 ◽

2006 ◽

Vol 21 (12) ◽

pp. 947-959 ◽

Cited By ~ 20

Author(s):

J. PONCE DE LEON

Keyword(s):

Extra Dimension ◽

New Physics ◽

Accelerated Expansion ◽

Effective Equation ◽

Higher Dimensional ◽

Internal Contradiction ◽

Frw Model ◽

Expansion Of The Universe ◽

The Universe ◽

Kaluza Klein

In braneworld models, Spacetime-Matter and other Kaluza–Klein theories, our spacetime is devised as a four-dimensional hypersurface orthogonal to the extra dimension in a five-dimensional bulk. We show that the FRW line element can be "reinvented" on a dynamical four-dimensional hypersurface, which is not orthogonal to the extra dimension, without any internal contradiction. This hypersurface is selected by the requirement of continuity of the metric and depends explicitly on the evolution of the extra dimension. The main difference between the "conventional" FRW, on an orthogonal hypersurface, and the new one is that the latter contains higher-dimensional modifications to the regular matter density and pressure in 4D. We compare the evolution of the spacetime in these two interpretations and find that a wealth of "new" physics can be derived from a five-dimensional metric if it is interpreted on a dynamical (non-orthogonal) 4D hypersurface. In particular, in the context of a well-known cosmological metric in 5D, we construct a FRW model which is consistent with the late accelerated expansion of the universe, while fitting simultaneously the observational data for the deceleration parameter. The model predicts an effective equation of state for the universe, which is consistent with observations.

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Fast approximate methods for modified gravity cosmological simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa333 ◽

2020 ◽

Vol 493 (2) ◽

pp. 2085-2100

Author(s):

Michal Vraštil ◽

Salman Habib

Keyword(s):

Modified Gravity ◽

Acoustic Oscillation ◽

Accelerated Expansion ◽

Minimal Extension ◽

Linear Regime ◽

Approximate Methods ◽

Perturbative Methods ◽

Non Linear ◽

Expansion Of The Universe ◽

The Universe

ABSTRACT The accelerated expansion of the Universe poses a major theoretical puzzle. Although the assumption of a non-zero cosmological constant provides a minimal extension of general relativity that is consistent with observational data, many theories of modified gravity have been suggested as possible alternatives. Predictions of structure formation for these models in the fully non-linear regime are very expensive and it is difficult, if not impossible, to explore such a huge space of models and parameters using high-resolution N-body simulations. Even in the mildly non-linear regime, perturbative methods can become extremely complex. We explore whether simplified dynamical approximations, applicable for a certain set of cosmological probes, can be used to investigate models of modified gravity with acceptable accuracy in the latter instance. For the case of chameleon gravity, we find that these methods can indeed be used to explore the region around the baryon acoustic oscillation scale, $k\sim 0.1~h\, \text{Mpc}^{-1}$ but not much further.

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Probing modified gravity in cosmic filaments

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833899 ◽

2018 ◽

Vol 619 ◽

pp. A122 ◽

Cited By ~ 3

Author(s):

Alex Ho ◽

Max Gronke ◽

Bridget Falck ◽

David F. Mota

Keyword(s):

Modified Gravity ◽

Gravity Models ◽

Accelerated Expansion ◽

Radial Density ◽

Post Process ◽

Global Properties ◽

Modified Gravity Theories ◽

Expansion Of The Universe ◽

Gravity Theories ◽

The Universe

Multiple modifications of general relativity (GR) have been proposed in the literature in order to understand the nature of the accelerated expansion of the Universe. However, thus far all the predictions of GR have been confirmed with constantly increasing accuracy. In this work, we study the imprints of a particular class of models – “screened” modified gravity theories – on cosmic filaments. We have utilized the N-body code ISIS/RAMSES to simulate the symmetron model and the Hu–Sawicky f(R) model, and we post-process the output with DisPerSE to identify the filaments of the cosmic web. We investigated how the global properties of the filaments – such as their lengths, masses, and thicknesses – as well as their radial density and speed profiles change under different gravity theories. We find that filaments are, on average, shorter and denser in modified gravity models compared to in ΛCDM. We also find that the speed profiles of the filaments are enhanced, consistent with theoretical expectations. Overall, our results suggest that cosmic filaments can be an effective complementary probe of screened modified gravity theories on Mpc scales.

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ACCELERATED EXPANSION IN MODIFIED GRAVITY WITH A YUKAWA-LIKE TERM

International Journal of Modern Physics D ◽

10.1142/s0218271807009838 ◽

2007 ◽

Vol 16 (04) ◽

pp. 687-697 ◽

Cited By ~ 23

Author(s):

K. ATAZADEH ◽

H. R. SEPANGI

Keyword(s):

Power Law ◽

Modified Gravity ◽

Newtonian Limit ◽

Accelerated Expansion ◽

Palatini Formalism ◽

Expansion Of The Universe ◽

Tensor Formulation ◽

The Universe ◽

Yukawa Term

We discuss the Palatini formulation of modified gravity including a Yukawa-like term. It is shown that in this formulation, the Yukawa term offers an explanation for the current exponential accelerated expansion of the universe and reduces to the standard Friedmann cosmology in the appropriate limit. We then discuss the scalar-tensor formulation of the model as a metric theory and show that the Yukawa term predicts a power-law acceleration at late-times. The Newtonian limit of the theory is also discussed in context of the Palatini formalism.

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Cosmological constant

10.1093/oso/9780198802877.003.0026 ◽

2018 ◽

Author(s):

Michael Kachelriess

Keyword(s):

Dark Energy ◽

Cosmological Constant ◽

Accelerated Expansion ◽

Vacuum Fluctuations ◽

Present Epoch ◽

Modify Gravity ◽

Expansion Of The Universe ◽

The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

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Taxonomy of Dark Energy Models

Universe ◽

10.3390/universe7060163 ◽

2021 ◽

Vol 7 (6) ◽

pp. 163

Author(s):

Verónica Motta ◽

Miguel A. García-Aspeitia ◽

Alberto Hernández-Almada ◽

Juan Magaña ◽

Tomás Verdugo

Keyword(s):

Dark Energy ◽

Cold Dark Matter ◽

Accelerated Expansion ◽

Energy Component ◽

The Past ◽

Energy Models ◽

The Status ◽

Expansion Of The Universe ◽

The Universe ◽

Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

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INFLATION, QUINTESSENCE PROBLEM AND VARYING SPEED OF LIGHT

Modern Physics Letters A ◽

10.1142/s0217732302006370 ◽

2002 ◽

Vol 17 (05) ◽

pp. 295-302

Author(s):

SUBENOY CHAKRABORTY

Keyword(s):

Cosmological Constant ◽

Accelerated Expansion ◽

Speed Of Light ◽

Expansion Of The Universe ◽

The Universe

In this paper it is shown that the present accelerated expansion of the Universe can be explained only by considering variation of the speed of light, without taking into account the cosmological constant or quintessence matter.

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Heuristic determination of the cosmological constant

Modern Physics Letters A ◽

10.1142/s0217732321501145 ◽

2021 ◽

pp. 2150114

Author(s):

Manuel Urueña Palomo ◽

Fernando Pérez Lara

Keyword(s):

Field Theory ◽

Energy Density ◽

Cosmological Constant ◽

Accelerated Expansion ◽

Fundamental Constants ◽

Quantum Field ◽

Brute Force ◽

Expansion Of The Universe ◽

The Universe

The vacuum catastrophe results from the disagreement between the theoretical value of the energy density of the vacuum in quantum field theory and the estimated one observed in cosmology. In a similar attempt in which the ultraviolet catastrophe was solved, we search for the value of the cosmological constant by brute-force through computation. We explore combinations of the fundamental constants in physics performing a dimensional analysis, in search of an equation resulting in the measured energy density of the vacuum or cosmological constant that is assumed to cause the accelerated expansion of the universe.

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Can accelerated expansion of the universe be due to spacetime vorticity?

Modern Physics Letters A ◽

10.1142/s0217732318502401 ◽

2018 ◽

Vol 33 (40) ◽

pp. 1850240

Author(s):

Babur M. Mirza

Keyword(s):

Magnetic Field ◽

Accelerated Expansion ◽

Newtonian Gravity ◽

Hubble’S Parameter ◽

Cosmic Expansion ◽

Zero Curvature ◽

Expansion Of The Universe ◽

General Relativistic ◽

The Universe ◽

The Magnetic Field

We present here a general relativistic mechanism for accelerated cosmic expansion and the Hubble’s parameter. It is shown that spacetime vorticity coupled to the magnetic field density in galaxies causes the galaxies to recede from one another at a rate equal to the Hubble’s constant. We therefore predict an oscillatory universe, with zero curvature, without assuming violation of Newtonian gravity at large distances or invoking dark energy/dark matter hypotheses. The value of the Hubble’s constant, along with the scale of expansion, as well as the high isotropy of CMB radiation are deduced from the model.

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