scholarly journals AN ALTERNATIVE INTERPRETATION FOR THE MODULI FIELDS OF THE COSMOLOGY ASSOCIATED TO TYPE IIB SUPERGRAVITY WITH FLUXES

2008 ◽  
Vol 23 (13) ◽  
pp. 1949-1962 ◽  
Author(s):  
TONATIUH MATOS ◽  
JOSÉ-RUBÉN LUÉVANO ◽  
HUGO GARCÍA-COMPEÁN ◽  
J. ALBERTO VÁZQUEZ
Keyword(s):  
Structure Formation ◽  
Alternative Interpretation ◽  
Linear Regime ◽  
Superstring Theory ◽  
Supergravity Theory ◽  
Cosmological Observations ◽  
Λcdm Model ◽  
Free Parameters ◽  
Quintessence Field ◽  
The Universe

The aim of this work is to provide a basis to interpret the dilaton as the dark matter of the universe, in the context of a particular cosmological model derived from type IIB supergravity theory with fluxes. In this theory, the dilaton is usually interpreted as a quintessence field. But, with this alternative interpretation we find that (in this supergravity model) the model gives a similar evolution and structure formation of the universe compared with the ΛCDM model in the linear regime of fluctuations of the structure formation. Some free parameters of the theory are fixed using the present cosmological observations. In the nonlinear regime there are some differences between the type IIB supergravity theory with the traditional CDM paradigm. The supergravity theory predicts the formation of galaxies earlier than the CDM and there is no density cusp in the center of galaxies. These differences can distinguish both models and might give a distinctive feature to the phenomenology of the cosmology coming from superstring theory with fluxes.

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.

A cyclic non-singular universe from Gauss–Bonnet and superstring corrections

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Rami Ahmad El-Nabulsi
Keyword(s):  
Scalar Field ◽  
Time Derivative ◽  
Low Energy ◽  
Exponential Potential ◽  
Field Equations ◽  
Superstring Theory ◽  
Higher Dimensional ◽  
Free Parameters ◽  
Higher Order Corrections ◽  
The Universe

Abstract In this study, we have constructed a viable cosmological model characterized by the presence of the Gauss–Bonnet four-dimensional invariant, higher-order corrections to the low energy effective action motivated from heterotic superstring theory and a general exponential potential comparable to those obtained in higher dimensional supergravities. The field equations were studied by assuming a particular relation between the Hubble parameter and the time derivative of the scalar field. It was observed that, for specific relations between the free parameters in the theory, the universe is cyclic, expands and contracts alternately without singularity with an equation of state oscillating around −1. The model is found to fit the recent astrophysical data.

scholarly journals THE LARGEST VIRIALIZED DARK HALO IN THE UNIVERSE

2002 ◽  
Vol 11 (08) ◽  
pp. 1189-1193
Author(s):  
WEI ZHOU ◽  
TONG-JIE ZHANG ◽  
LI CHEN ◽  
XIANG-TAO HE ◽  
YU-MEI HUANG
Keyword(s):  
Structure Formation ◽  
Temperature Increase ◽  
Analytic Approach ◽  
Dark Halo ◽  
Clusters Of Galaxies ◽  
Λcdm Model ◽  
Present Universe ◽  
Virial Mass ◽  
The Universe ◽  
Rule Out

Using semi-analytic approach, we present an estimate of the properties of the largest virialized dark halos in the present universe for three different scenarios of structure formation: SCDM, ΛCDM and OCDM models. The resulting virial mass and temperature increase from the lowest values of 1.6 × 1015 h-1 M⊙ and 9.8 keV in OCDM, the mid-range values of 9.0 × 1015 h-1 M⊙ and 31 keV in ΛCDM, to the highest values of 20.9 × 1015h-1M⊙, 65 keV in SCDM. As compared with the largest virialized object seen in the universe, the richest clusters of galaxies, we can safely rule out the OCDM model. In addition, the SCDM model is very unlikely because of the unreasonably high virial mass and temperature. Our computation favors the prevailing ΛCDM model in which superclusters may be marginally regarded as dynamically-virialized systems.

scholarly journals LARGE SCALE ANISOTROPY DUE TO PRE-INFLATIONARY PHASE OF COSMIC EVOLUTION

2012 ◽  
Vol 27 (04) ◽  
pp. 1250014 ◽  
Author(s):  
PAVAN K. ALURI ◽  
PANKAJ JAIN
Keyword(s):  
Large Scale ◽  
Cosmological Evolution ◽  
Cosmic Evolution ◽  
Cosmological Observations ◽  
Inflationary Phase ◽  
The Universe ◽  
Dipole Modulation

We show that perturbations generated during the anisotropic pre-inflationary stage of cosmic evolution may affect cosmological observations today for a certain range of parameters. Due to the anisotropic nature of the universe during such early times, it might explain some of the observed signals of large scale anisotropy. In particular, we argue that the alignment of CMB quadrupole and octopole may be explained by the Sachs–Wolfe effect due to the large scale anisotropic modes from very early times of cosmological evolution. We also comment on how the observed dipole modulation of CMB power may be explained within this framework.

scholarly journals Estimate of energy constituents of the universe in ΛCDM

2017 ◽  
Vol 95 (1) ◽  
pp. 21-24
Author(s):  
Jung-Jeng Huang ◽  
Meng-Jong Wang
Keyword(s):  
Maximal Entropy ◽  
Extended Version ◽  
Cosmic Scale ◽  
Λcdm Model ◽  
The Universe ◽  
Entropy Of The Universe

We propose that the Hubble law can be viewed as the de Broglie relation on a cosmic scale. We show how the entropy of the Universe can be estimated in the ΛCDM model and its extended version, and how the quest for the maximal entropy leads to the energy constituents of the current Universe.

scholarly journals Collisionless Dynamics and the Cosmic Web

2014 ◽  
Vol 11 (S308) ◽  
pp. 87-96
Author(s):  
Oliver Hahn
Keyword(s):  
Dark Matter ◽  
Structure Formation ◽  
Large Scale ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Maximum Amount ◽  
Lagrangian Manifold ◽  
Linear Regime ◽  
Fine Grained ◽  
Simulation Techniques

AbstractI review the nature of three-dimensional collapse in the Zeldovich approximation, how it relates to the underlying nature of the three-dimensional Lagrangian manifold and naturally gives rise to a hierarchical structure formation scenario that progresses through collapse from voids to pancakes, filaments and then halos. I then discuss how variations of the Zeldovich approximation (based on the gravitational or the velocity potential) have been used to define classifications of the cosmic large-scale structure into dynamically distinct parts. Finally, I turn to recent efforts to devise new approaches relying on tessellations of the Lagrangian manifold to follow the fine-grained dynamics of the dark matter fluid into the highly non-linear regime and both extract the maximum amount of information from existing simulations as well as devise new simulation techniques for cold collisionless dynamics.

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.

GROWTH INDEX AND MODIFIED GRAVITY

2011 ◽  
Vol 01 ◽  
pp. 228-233
Author(s):  
YUNGUI GONG
Keyword(s):  
Growth Rate ◽  
Dark Energy ◽  
Modified Gravity ◽  
Growth Index ◽  
Accurate Approximation ◽  
Energy Models ◽  
Λcdm Model ◽  
The Universe ◽  
Matter Energy ◽  
Matter Perturbation

The growth rate of matter perturbation and the expansion rate of the Universe can be used to distinguish modified gravity and dark energy models. Remarkably, the growth rate can be approximated as Ωγ. We discuss the dependence of the growth index γ on the dimensionless matter energy density Ω for a more accurate approximation of the growth factor. The observational data are used to fit different models. The data strongly disfavor the Dvali-Gabadadze-Porrati model. For the ΛCDM model, we find that [Formula: see text]. For the Dvali-Gabadadze-Porrati model, we find that [Formula: see text].

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