scholarly journals COSMOLOGICAL ACCELERATION FROM STRUCTURE FORMATION

2006 ◽  
Vol 15 (12) ◽  
pp. 2141-2146 ◽  
Author(s):  
SYKSY RÄSÄNEN
Keyword(s):  
Structure Formation ◽  
Gravitational Collapse ◽  
Physical Meaning ◽  
Expansion Rate ◽  
Small Perturbations ◽  
Local Expansion ◽  
The Universe ◽  
Friedmann Robertson Walker ◽  
Dust Universe

We discuss the Buchert equations, which describe the average expansion of an inhomogeneous dust universe. In the limit of small perturbations, they reduce to the Friedmann–Robertson–Walker equations. However, when the universe is very inhomogeneous, the behavior can be qualitatively different from the FRW case. In particular, the average expansion rate can accelerate even though the local expansion rate decelerates everywhere. We clarify the physical meaning of this paradoxical feature with a simple toy model, and demonstrate how acceleration is intimately connected with gravitational collapse. This provides a link to structure formation, which in turn has a preferred time around the era when acceleration has been observed to start.

scholarly journals THE EFFECT OF STRUCTURE FORMATION ON THE EXPANSION OF THE UNIVERSE

2008 ◽  
Vol 17 (13n14) ◽  
pp. 2543-2548 ◽  
Author(s):  
SYKSY RÄSÄNEN
Keyword(s):  
Structure Formation ◽  
Cold Dark Matter ◽  
Expansion Rate ◽  
Isotropic Case ◽  
Isotropic Distribution ◽  
Expansion Of The Universe ◽  
Free Parameters ◽  
Matter Transfer ◽  
The Universe ◽  
Dust Universe

Observations of the expansion rate of the universe at late times disagree by a factor of 1.5–2 with the prediction of homogeneous and isotropic models based on ordinary matter and gravity. We discuss how the departure from linearly perturbed homogeneity and isotropy due to structure formation could explain this discrepancy. We evaluate the expansion rate in a dust universe which contains nonlinear structures with a statistically homogeneous and isotropic distribution. The expansion rate is found to increase relative to the exactly homogeneous and isotropic case by a factor of 1.1–1.3 at some tens of billions of years. The time scale follows from the cold dark matter transfer function and the amplitude of primordial perturbations without additional free parameters.

scholarly journals The Finslerian quantum cosmology

2020 ◽  
Vol 98 (9) ◽  
pp. 862-868
Author(s):  
S.S. De ◽  
Farook Rahaman ◽  
Nupur Paul
Keyword(s):  
Wave Function ◽  
Cosmological Model ◽  
Time Evolution ◽  
Physical Meaning ◽  
Quantum Cosmology ◽  
Constraint Equation ◽  
Quantum Mechanical ◽  
Expectation Value ◽  
The Universe ◽  
Friedmann Robertson Walker

We present a Friedmann–Robertson–Walker quantum cosmological model within the framework of Finslerian geometry. In this work, we consider a specific fluid. We obtain the corresponding Wheeler–DeWitt equation as the usual constraint equation as well as the Schrödinger equation following Dirac, although the approaches yield the same time-independent equation for the wave function of the universe. We provide exact classical and quantum mechanical solutions. We use eigenfunctions to study the time evolution of the expectation value of the scale factor. Finally, we discuss the physical meaning of the results.

scholarly journals A Cepheid distance to the Fornax cluster and the local expansion rate of the Universe

Nature ◽  
10.1038/25678 ◽  
1998 ◽  
Vol 395 (6697) ◽  
pp. 47-50 ◽  
Author(s):  
Barry F. Madore ◽  
Wendy L. Freedman ◽  
N. Silbermann ◽  
Paul Harding ◽  
John Huchra ◽  
...  
Keyword(s):  
Expansion Rate ◽  
Local Expansion ◽  
Fornax Cluster ◽  
The Universe

Signature change in p-adic and noncommutative FRW cosmology

2014 ◽  
Vol 29 (27) ◽  
pp. 1450155 ◽  
Author(s):  
Goran S. Djordjevic ◽  
Ljubisa Nesic ◽  
Darko Radovancevic
Keyword(s):  
Loop Quantum Gravity ◽  
Initial Conditions ◽  
Planck Scale ◽  
The Other ◽  
Frw Cosmology ◽  
Signature Change ◽  
Discrete Nature ◽  
Frw Metric ◽  
The Universe ◽  
Friedmann Robertson Walker

The significant matter for the construction of the so-called no-boundary proposal is the assumption of signature transition, which has been a way to deal with the problem of initial conditions of the universe. On the other hand, results of Loop Quantum Gravity indicate that the signature change is related to the discrete nature of space at the Planck scale. Motivated by possibility of non-Archimedean and/or noncommutative structure of space–time at the Planck scale, in this work we consider the classical, p-adic and (spatial) noncommutative form of a cosmological model with Friedmann–Robertson–Walker (FRW) metric coupled with a self-interacting scalar field.

Investigating cosmology with equation of state

2019 ◽  
Vol 97 (7) ◽  
pp. 752-760 ◽  
Author(s):  
M. Farasat Shamir ◽  
Adnan Malik
Keyword(s):  
Equation Of State ◽  
Exact Solutions ◽  
Scalar Potential ◽  
State Parameter ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Radiation Universe ◽  
Modified Formula ◽  
Friedmann Robertson Walker ◽  
Dust Universe

The aim of this paper is to investigate the field equations of modified [Formula: see text] theory of gravity, where R and [Formula: see text] represent the Ricci scalar and scalar potential, respectively. We consider the Friedmann–Robertson–Walker space–time for finding some exact solutions by using different values of equation of state parameter. In this regard, different possibilities of the exact solutions have been discussed for dust universe, radiation universe, ultra-relativistic universe, sub-relativistic universe, stiff universe, and dark energy universe. Mainly power law and exponential forms of the scale factor are chosen for the analysis.

scholarly journals Supercomputer simulations of structure formation in the Universe

2016 ◽  
Vol 12 (S325) ◽  
pp. 10-16
Author(s):  
Tomoaki Ishiyama
Keyword(s):  
Domain Decomposition ◽  
Structure Formation ◽  
Short Range ◽  
Large Scale ◽  
Massively Parallel ◽  
Average Performance ◽  
And Performance ◽  
Performance Results ◽  
The Universe ◽  
Peak Speed

AbstractWe describe the implementation and performance results of our massively parallel MPI†/OpenMP‡ hybrid TreePM code for large-scale cosmological N-body simulations. For domain decomposition, a recursive multi-section algorithm is used and the size of domains are automatically set so that the total calculation time is the same for all processes. We developed a highly-tuned gravity kernel for short-range forces, and a novel communication algorithm for long-range forces. For two trillion particles benchmark simulation, the average performance on the fullsystem of K computer (82,944 nodes, the total number of core is 663,552) is 5.8 Pflops, which corresponds to 55% of the peak speed.

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