scholarly journals COSMIC ACCELERATION AND M THEORY COSMOLOGY

2004 ◽  
Vol 19 (13n16) ◽  
pp. 1093-1098 ◽  
Author(s):  
ISHWAREE P. NEUPANE
Keyword(s):  
Dark Energy ◽  
First Principles ◽  
Cosmic Acceleration ◽  
Curved Spaces ◽  
Short Overview ◽  
M Theory

This is a short overview of spatially flat (or open) four-dimensional accelerating cosmologies for some simple exponential potentials obtained by string or M theory compactification on some non-trivial curved spaces, which may lead to some striking results, e.g., the observed cosmic acceleration and the scale of the dark energy from first principles.

scholarly journals Multi-field dark energy: Cosmic acceleration on a steep potential

2021 ◽  
pp. 136427
Author(s):  
Yashar Akrami ◽  
Misao Sasaki ◽  
Adam R. Solomon ◽  
Valeri Vardanyan
Keyword(s):  
Dark Energy ◽  
Cosmic Acceleration

scholarly journals MODIFIED GRAVITY AS A COMMON CAUSE FOR COSMIC ACCELERATION AND FLAT GALAXY ROTATION CURVES

2012 ◽  
Vol 21 (11) ◽  
pp. 1242002 ◽  
Author(s):  
PRITI MISHRA ◽  
TEJINDER P. SINGH
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmic Acceleration ◽  
Accelerating Universe ◽  
Rotation Curves ◽  
Common Cause ◽  
Order Of Magnitude ◽  
Flat Rotation Curves ◽  
Acceleration Of The Universe ◽  
Galaxy Rotation Curves

Flat galaxy rotation curves and the accelerating Universe both imply the existence of a critical acceleration, which is of the same order of magnitude in both the cases, in spite of the galactic and cosmic length scales being vastly different. Yet, it is customary to explain galactic acceleration by invoking gravitationally bound dark matter, and cosmic acceleration by invoking a "repulsive" dark energy. Instead, might it not be the case that the flatness of rotation curves and the acceleration of the Universe have a common cause? In this essay we propose a modified theory of gravity. By applying the theory on galactic scales we demonstrate flat rotation curves without dark matter, and by applying it on cosmological scales we demonstrate cosmic acceleration without dark energy.

RICCION AS A COSMIC DARK MATTER CANDIDATE AND LATE COSMIC ACCELERATION

2008 ◽  
Vol 23 (31) ◽  
pp. 2681-2689
Author(s):  
S. K. SRIVASTAVA ◽  
K. P. SINHA
Keyword(s):  
Energy Source ◽  
Dark Matter ◽  
Dark Energy ◽  
Cosmic Acceleration ◽  
Exotic Matter ◽  
Dark Matter Candidate ◽  
Classical Level ◽  
The Past ◽  
Higher Derivative

In the past few years, a possibility is investigated, where curvature itself behaves as a source of dark energy. So, it is natural to think whether curvature can produce dark matter too. It is found that, at classical level, higher-derivative gravity yields curvature inspired particles namely riccions.31 Here, it is probed whether riccion can be a possible source of dark matter. Further, it is found that the late universe accelerates. Here, it is interesting to see that acceleration is obtained from curvature without using any dark energy source of exotic matter.

Bouncing scenario in Brans–Dicke theory

2020 ◽  
Vol 17 (04) ◽  
pp. 2050056
Author(s):  
Sunil Kumar Tripathy ◽  
Subingya Pandey ◽  
Alaka Priyadarsini Sendha ◽  
Dipanjali Behera
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Linear Equation ◽  
Scale Factor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Dark Fluid

A bouncing scenario is studied in the framework of generalized Brans–Dicke theory. In order to have a dark energy (DE) driven late time cosmic acceleration, we have considered a unified dark fluid simulated by a linear equation of state (EoS). The evolutionary behavior of the DE equation of parameter derived from the unified dark fluid has been discussed. The effect of the bouncing scale factor on the Brans–Dicke parameter, self-interacting potential and the Brans–Dicke scalar field is investigated.

scholarly journals MODIFIED GRAVITATIONAL THEORIES AND COSMIC ACCELERATION

2004 ◽  
Vol 19 (31) ◽  
pp. 5343-5350 ◽  
Author(s):  
DAMIEN A. EASSON
Keyword(s):  
Dark Energy ◽  
Cosmic Acceleration ◽  
Late Time ◽  
De Sitter ◽  
Gravitational Theories ◽  
Hilbert Action

Modified gravitational theories can provide alternatives to dark energy as an explaination for the observed late-time cosmic acceleration. Several examples of low-curvature corrections to the Einstein-Hilbert action are studied. These models generically contain unstable de Sitter solutions and, depending on the parameters of the theory, can exhibit late time accelerating attractor solutions.

scholarly journals A COSMOLOGICAL MODEL WITH FERMIONIC FIELD

2010 ◽  
Vol 25 (13) ◽  
pp. 2735-2746 ◽  
Author(s):  
R. RAKHI ◽  
G. V. VIJAYAGOVINDAN ◽  
K. INDULEKHA
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
The Self ◽  
Late Time ◽  
Fermionic Field ◽  
Energy Field ◽  
Late Time Acceleration ◽  
Higher Order Terms ◽  
Interaction Term ◽  
M Theory

In this work, a cosmological model inspired by string/M-theory with fermionic field is taken into consideration. Here it is investigated whether the introduction of a non-Dirac fermionic field — characterized by an interaction term — affects the cosmological evolution. The self-interaction potential is considered as a combination of the scalar and pseudoscalar invariants. It is observed that the fermionic field under consideration behaves like an inflation field for the early universe and later on, as a dark energy field. The late time acceleration becomes more prominent by the addition of the interaction term. There is a slight decrease for the inflation peak as well as for the energy density. We see that the addition of higher-order terms to the fermionic part of Lagrangian does not significantly change either the inflation or the late time acceleration behavior.

scholarly journals An accelerating cosmological model from a parametrization of Hubble parameter

2019 ◽  
Vol 35 (05) ◽  
pp. 2050011 ◽  
Author(s):  
S. K. J. Pacif ◽  
Md Salahuddin Khan ◽  
L. K. Paikroy ◽  
Shalini Singh
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
Hubble Parameter ◽  
Cosmological Parameters ◽  
Cosmic Time ◽  
Solution Procedure ◽  
Cosmic Acceleration ◽  
Model Parameters ◽  
Late Time ◽  
Field Equations

In view of late-time cosmic acceleration, a dark energy cosmological model is revisited wherein Einstein’s cosmological constant is considered as a candidate of dark energy. Exact solution of Einstein field equations (EFEs) is derived in a homogeneous isotropic background in classical general relativity. The solution procedure is adopted in a model-independent way (or the cosmological parametrization). A simple parametrization of the Hubble parameter (H) as a function of cosmic time t is considered which yields an exponential type of evolution of the scale factor (a) and also shows a negative value of deceleration parameter at the present time with a signature flip from early deceleration to late acceleration. Cosmological dynamics of the model obtained have been discussed illustratively for different phases of the evolution of the universe. The evolution of different cosmological parameters is shown graphically for flat and closed cases of Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime for the presented model (open case is incompatible to the present scenario). We have also constrained our model parameters with the updated (36 points) observational Hubble dataset.

scholarly journals Late-time cosmic acceleration: ABCD of dark energy and modified theories of gravity

2016 ◽  
Vol 25 (12) ◽  
pp. 1630031 ◽  
Author(s):  
M. Sami ◽  
R. Myrzakulov
Keyword(s):  
Dark Energy ◽  
Scalar Fields ◽  
Massive Gravity ◽  
Cosmic Acceleration ◽  
Modified Theories Of Gravity ◽  
Late Time ◽  
Cosmological Constant Problem ◽  
Chameleon Mechanism ◽  
Theories Of Gravity ◽  
Basic Ideas

We briefly review the problems and prospects of the standard lore of dark energy. We have shown that scalar fields, in principle, cannot address the cosmological constant problem. Indeed, a fundamental scalar field is faced with a similar problem dubbed naturalness. In order to keep the discussion pedagogical, aimed at a wider audience, we have avoided technical complications in several places and resorted to heuristic arguments based on physical perceptions. We presented underlying ideas of modified theories based upon chameleon mechanism and Vainshtein screening. We have given a lucid illustration of recently investigated ghost-free nonlinear massive gravity. Again, we have sacrificed rigor and confined to the basic ideas that led to the formulation of the theory. The review ends with a brief discussion on the difficulties of the theory applied to cosmology.

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