COSMIC EVOLUTION: A FEW CONCLUDING REMARKS

A recent work proposed that the recent cosmic passage to a cosmic acceleration era is the result of the existence of small anti-gravity sources in each galaxy and clusters of galaxies. In particular, a Swiss-cheese cosmology model, which relativistically integrates the contribution of all these anti-gravity sources on a galactic scale has been constructed assuming the presence of an infrared fixed point for a scale dependent cosmological constant. The derived cosmological expansion provides an explanation for both the fine tuning and the coincidence problem. The present work relaxes the previous assumption on the running of the cosmological constant and allows for a generic scaling around the infrared fixed point. Our analysis reveals that, in order to produce a cosmic evolution consistent with the best ΛCDM model, the IR-running of the cosmological constant is consistent with the presence of an IR-fixed point.

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Cosmic Evolution of Viscous QCD Epoch in Causal Eckart Frame

Universe ◽

10.3390/universe7050112 ◽

2021 ◽

Vol 7 (5) ◽

pp. 112

Author(s):

Eman Abdel Hakk ◽

Abdel Nasser Tawfik ◽

Afaf Nada ◽

Hayam Yassin

Keyword(s):

Energy Density ◽

Energy Flow ◽

Equations Of State ◽

Temporal Evolution ◽

Particle Diffusion ◽

Cosmic Evolution ◽

Bulk Viscous ◽

Viscous Pressure ◽

Bulk Viscous Pressure ◽

Particle Current

It is conjectured that in cosmological applications the particle current is not modified but finite heat or energy flow. Therefore, comoving Eckart frame is a suitable choice, as it merely ceases the charge and particle diffusion and conserves charges and particles. The cosmic evolution of viscous hadron and parton epochs in casual and non-casual Eckart frame is analyzed. By proposing equations of state deduced from recent lattice QCD simulations including pressure p, energy density ρ, and temperature T, the Friedmann equations are solved. We introduce expressions for the temporal evolution of the Hubble parameter H˙, the cosmic energy density ρ˙, and the share η˙ and the bulk viscous coefficient ζ˙. We also suggest how the bulk viscous pressure Π could be related to H. We conclude that the relativistic theory of fluids, the Eckart frame, and the finite viscous coefficients play essential roles in the cosmic evolution, especially in the hadron and parton epochs.

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

Modern Physics Letters A ◽

10.1142/s0217732312500149 ◽

2012 ◽

Vol 27 (04) ◽

pp. 1250014 ◽

Cited By ~ 15

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.

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FOLLOWING THE COSMIC EVOLUTION OF PRISTINE GAS. I. IMPLICATIONS FOR MILKY WAY HALO STARS

The Astrophysical Journal ◽

10.3847/1538-4357/834/1/23 ◽

2016 ◽

Vol 834 (1) ◽

pp. 23 ◽

Cited By ~ 19

Author(s):

Richard Sarmento ◽

Evan Scannapieco ◽

Liubin Pan

Keyword(s):

Milky Way ◽

Halo Stars ◽

Cosmic Evolution ◽

Milky Way Halo

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Field Independent Cosmic Evolution

Journal of Astrophysics ◽

10.1155/2013/590171 ◽

2013 ◽

Vol 2013 ◽

pp. 1-12 ◽

Cited By ~ 5

Author(s):

Nayem Sk ◽

Abhik Kumar Sanyal

Keyword(s):

Higher Order ◽

Noether Symmetry ◽

Scalar Tensor Theory ◽

Anisotropic Model ◽

Tachyonic Field ◽

Tensor Theory ◽

Cosmic Evolution ◽

Field Independent ◽

Conserved Current ◽

Theory Of Gravity

It has been shown earlier that Noether symmetry does not admit a form of corresponding to an action in which is coupled to scalar-tensor theory of gravity or even for pure theory of gravity taking anisotropic model into account. Here, we prove that theory of gravity does not admit Noether symmetry even if it is coupled to tachyonic field and considering a gauge in addition. To handle such a theory, a general conserved current has been constructed under a condition which decouples higher-order curvature part from the field part. This condition, in principle, solves for the scale-factor independently. Thus, cosmological evolution remains independent of the form of the chosen field, whether it is a scalar or a tachyon.

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