scholarly journals ACCELERATING EXPANSION OF THE UNIVERSE MAY BE CAUSED BY INHOMOGENEITIES

2006 ◽  
Vol 21 (14) ◽  
pp. 1117-1125 ◽  
Author(s):  
GYULA BENE ◽  
VIKTOR CZINNER ◽  
MÁTYÁS VASÚTH
Keyword(s):  
Friedmann Equation ◽  
Additional Term ◽  
Density Fluctuations ◽  
Einstein Equations ◽  
The Other ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Homogeneous Approximation ◽  
Spatial Inhomogeneities

We point out that, due to the nonlinearity of the Einstein equations, a homogeneous approximation in cosmology leads to the appearance of an additional term in the Friedmann equation. This new term is associated with the spatial inhomogeneities of the metric and can be expressed in terms of density fluctuations. Although it is not constant, it decays much slower (as t-2/3) than the other terms (like density) which decrease as t-2. The presence of the new term leads to a correction in the scale factor that is proportional to t2and may give account of the recently observed accelerating expansion of the universe without introducing a cosmological constant.

scholarly journals Almost-Pseudo-Ricci Symmetric FRW Universe with a Dynamic Cosmological Term and Equation of State

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 205
Author(s):  
Sanjay Mandal ◽  
Avik De ◽  
Tee-How Loo ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Equation Of State ◽  
Cosmological Parameters ◽  
Cosmological Term ◽  
Ricci Scalar ◽  
Energy Conditions ◽  
Late Time ◽  
Frw Universe ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

The objective of the present paper is to investigate an almost-pseudo-Ricci symmetric FRW spacetime with a constant Ricci scalar in a dynamic cosmological term Λ(t) and equation of state (EoS) ω(t) scenario. Several cosmological parameters are calculated in this setting and thoroughly studied, which shows that the model satisfies the late-time accelerating expansion of the universe. We also examine all of the energy conditions to check our model’s self-stability.

Spectral redshift does not imply an accelerating expansion of the universe

2013 ◽  
Vol 26 (3) ◽  
pp. 452-456
Author(s):  
Dimitrios Laskaroudis
Keyword(s):  
Red Shift ◽  
Gravity Center ◽  
Erroneous Conclusion ◽  
Minimum Value ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Creation ◽  
The Universe ◽  
Spectral Redshift

Spectra received from faraway heavenly objects display a redshift. In this paper, it is shown that there is a moment in time tx at which time the red shift has its minimum value. This moment is different for every object and depends on the distance of the emission from the gravity center of the object. So from the time of the creation of the object and up until the time tx, the red shift is decreasing and from that moment on it is increasing while the object, due to the expansion of the universe, continues to move away with decreasing speed. Due to the change of the red shift from decreasing to increasing, it is possible to observe faraway supernovas with a brightness that is less than what is expected. This observation leads to the erroneous conclusion that the universe is expanding with acceleration. Finally, an explanation is given to the fact that the number of quasars is decreasing in time.

scholarly journals BARYOGENESIS VIA DENSITY FLUCTUATIONS WITH A SECOND ORDER ELECTROWEAK PHASE TRANSITION

2003 ◽  
Vol 18 (26) ◽  
pp. 4851-4868 ◽  
Author(s):  
BISWANATH LAYEK ◽  
SOMA SANYAL ◽  
AJIT M. SRIVASTAVA
Keyword(s):  
Phase Transition ◽  
Baryon Asymmetry ◽  
Density Fluctuations ◽  
Second Order ◽  
Baryon Production ◽  
Electroweak Phase Transition ◽  
Expansion Of The Universe ◽  
Second Order Transition ◽  
Background Temperature ◽  
The Universe

We consider the presence of cosmic string induced density fluctuations in the universe at temperatures below the electroweak phase transition temperature. Resulting temperature fluctuations can restore the electroweak symmetry locally, depending on the amplitude of fluctuations and the background temperature. The symmetry will be spontaneously broken again in a given fluctuation region as the temperature drops there (for fluctuations with length scales smaller than the horizon), resulting in the production of baryon asymmetry. The time scale of the transition will be governed by the wavelength of fluctuation and, hence, can be much smaller than the Hubble time. This leads to strong enhancement in the production of baryon asymmetry for a second order electroweak phase transition as compared to the case when transition happens due to the cooling of the universe via expansion. For a two-Higgs extension of the Standard Model (with appropriate CP violation), we show that one can get the required baryon to entropy ratio if fluctuations propagate without getting significantly damped. If fluctuations are damped rapidly, then a volume factor suppresses the baryon production. Still, the short scale of the fluctuation leads to enhancement of the baryon to entropy ratio by at least 3–4 orders of magnitude compared to the conventional case of second order transition where the cooling happens due to expansion of the universe.

scholarly journals MULTIDIMENSIONAL GRAVITATIONAL MODEL WITH ANISOTROPIC PRESSURE

2013 ◽  
Vol 22 (13) ◽  
pp. 1350075 ◽  
Author(s):  
O. A. GRIGORIEVA ◽  
G. S. SHAROV
Keyword(s):  
Equations Of State ◽  
Einstein Equations ◽  
Accelerated Expansion ◽  
Anisotropic Pressure ◽  
Gravitational Model ◽  
Spatial Dimensions ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Ia Supernovae ◽  
The Universe

We consider the gravitational model with additional spatial dimensions and anisotropic pressure which is nonzero only in these dimensions. Cosmological solutions of the Einstein equations in this model include accelerated expansion of the universe at late stage of its evolution and dynamical compactification of extra dimensions. This model describes observational data for Type Ia supernovae on the level or better than the ΛCDM model. We analyze two equations of state resulting in different predictions for further evolution, but in both variants the acceleration epoch is finite.

Swampland criteria and cosmological behavior of Tsallis holographic dark energy in Bianchi -III Universe

2020 ◽  
Vol 17 (07) ◽  
pp. 2050098 ◽  
Author(s):  
Umesh Kumar Sharma ◽  
Shikha Srivastava ◽  
A. Beesham
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Accelerating Universe ◽  
Accelerating Expansion ◽  
Bianchi Iii ◽  
Expansion Of The Universe ◽  
Hubble Horizon ◽  
The Universe ◽  
Universe Evolution

In this paper, a new form of dark energy, known as Tsallis holographic dark energy (THDE), with IR cutoff as Hubble horizon proposed by Tavayef et al. Tsallis holographic dark energy, Phys. Lett. B 781 (2018) 195 has been explored in Bianchi-III model with the matter. By taking the time subordinate deceleration parameter, the solution of Einstein’s field equation is found. The Universe evolution from earlier decelerated to the current accelerated phase is exhibited by the deceleration parameter acquired in the THDE model. It can be seen that the derived THDE model is related to an accelerating Universe with quintessence ([Formula: see text]). The squared sound speed [Formula: see text] also suggests that the THDE model is classically stable at present. In addition, the quintessence phase of the THDE model is analyzed with swampland conjecture to reformulate the accelerating expansion of the Universe.

Rotation as a Source of Accelerating Expansion of the Universe

2021 ◽  
Author(s):  
Andrzej Szummer
Keyword(s):  
Gravitational Force ◽  
Cosmological Parameters ◽  
Classical Mechanics ◽  
Astronomical Observations ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Difference ◽  
Changes Over Time ◽  
The Universe ◽  
Over Time

Abstract Assuming a hypothesis, that the universe is rotating from the very beginning – as soon as it appeared- creates new possibilities to explain accelerating expansion of the universe. A spinning universe is under the action of two enormous forces: gravitational force and centrifugal force. The difference between the two forces has been shown to give the resultant force that causes the expansion of the universe to accelerate. Applying classical mechanics as a method, I calculated the magnitude of this acceleration, the time when it appeared and how it changes over time. By applying only recognized cosmological parameters, interesting results were obtained that can be checked with astronomical observations. The presence of acceleration of expansion causes the rate of expansion of the universe to continue to increase, which is consistent with astronomical observations. However, the speed of this increase in the rate of expansion becomes slower over time.

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