scholarly journals Cosmological constant and late transient acceleration of the universe in the Horava–Witten heterotic M-theory on S1/Z2

2008 ◽  
Vol 663 (3) ◽  
pp. 147-151 ◽  
Author(s):  
Yungui Gong ◽  
Anzhong Wang ◽  
Qiang Wu
Keyword(s):  
Cosmological Constant ◽  
Acceleration Of The Universe ◽  
M Theory ◽  
The Universe

scholarly journals Explaining Dark Energy, Small Cosmological Constant and Inflation Without New Physics?

2020 ◽  
Author(s):  
Stephane Maes
Keyword(s):  
Dark Energy ◽  
Random Walk ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
New Physics ◽  
Vacuum Energy Density ◽  
Beyond The Standard Model ◽  
Exponential Expansion ◽  
Acceleration Of The Universe ◽  
The Universe

In a multi-fold universe, gravity emerges from entanglement and spacetime is discrete, with a fractal structure based on random walk and a non-commutative geometry. When random walk is combined with maximal particle generations, exponential expansion can automatically takes place. Away from maximal generation or in an already concretized spacetime, random walk accounts for a constant or slowing down expansion. Meanwhile, the multi-fold mechanisms also implies a constant expansion potential, adding a force to the expansion of the universe, thanks to uncertainties. It explain the constant acceleration of the universe expansion with a cosmological constant that is not the vacuum energy density but can be way smaller.It may contribute to addressing problems like the absence of any explanation of dark energy, the embarrassing orders of magnitude of discrepancies between vacuum energy and the cosmological constant predicted by conventional Physics; issues that are among Today’s biggest mysteries of the universe. These explanations do not require New Physics beyond the Standard Model and the Standard Cosmology Model.

scholarly journals ON THE TOPOLOGICAL NATURE OF THE COSMOLOGICAL CONSTANT

2012 ◽  
Vol 18 ◽  
pp. 109-114
Author(s):  
M. D. MAIA
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Cosmic Radiation ◽  
Cosmic Time ◽  
Space Time ◽  
Time Flow ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Topological Changes

It is shown that topological changes in space-time are necessary to make General Relativity compatible with the Newtonian limit and to solve the hierarchy of the fundamental interactions. We detail how topology and topological changes appear in General Relativity and how it leaves an observable footprint in space-time. In cosmology we show that such topological observable is the cosmic radiation produced by the acceleration of the universe. The cosmological constant is a very particular case which occurs when the expansion of the universe into the vacuum occurs only in the direction of the cosmic time flow.

scholarly journals Accelerated expansion induced by Dark Matter with two charges

2021 ◽  
Author(s):  
Steen H Hansen
Keyword(s):  
Dark Matter ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Microwave Background ◽  
Dynamic Variations ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
Internal Velocity ◽  
The Universe ◽  
Range Force

Abstract The accelerated expansion of the universe has been established through observations of supernovae, the growth of structure, and the cosmic microwave background. The most popular explanation is Einsteins cosmological constant, or dynamic variations hereof. A recent paper demonstrated that if dark matter particles are endowed with a repulsive force proportional to the internal velocity dispersion of galaxies, then the corresponding acceleration of the universe may follow that of a cosmological constant fairly closely. However, no such long-range force is known to exist. A concrete example of such a force is derived here, by equipping the dark matter particles with two new dark charges. This result lends support to the possibility that the current acceleration of the universe may be explained without the need for a cosmological constant.

scholarly journals CosMIn: THE SOLUTION TO THE COSMOLOGICAL CONSTANT PROBLEM

2013 ◽  
Vol 22 (12) ◽  
pp. 1342001 ◽  
Author(s):  
HAMSA PADMANABHAN ◽  
T. PADMANABHAN
Keyword(s):  
Cosmological Constant ◽  
Theoretical Physics ◽  
Cosmological Constant Problem ◽  
Holy Grail ◽  
Cosmic Evolution ◽  
Inflationary Phase ◽  
Acceleration Of The Universe ◽  
Hubble Radius ◽  
Theoretical Considerations ◽  
The Universe

The current acceleration of the universe can be modeled in terms of a cosmological constant Λ. We show that the extremely small value of [Formula: see text], the holy grail of theoretical physics, can be understood in terms of a new, dimensionless, conserved number Cosmic Mode Index (CosMIn), which counts the number of modes crossing the Hubble radius during the three phases of evolution of the universe. Theoretical considerations suggest that N ≈ 4π. This single postulate leads us to the correct, observed numerical value of the cosmological constant! This approach also provides a unified picture of cosmic evolution relating the early inflationary phase to the late accelerating phase.

scholarly journals Fundamental constants and cosmic vacuum: The micro and macro connection

2015 ◽  
Vol 30 (22) ◽  
pp. 1540034 ◽  
Author(s):  
Harald Fritzsch ◽  
Joan Solà
Keyword(s):  
Cosmological Constant ◽  
Vacuum Energy Density ◽  
Fundamental Constants ◽  
Cosmic Expansion ◽  
Long Time ◽  
Acceleration Of The Universe ◽  
The Masses ◽  
The Universe ◽  
Cosmic History ◽  
Constants Of Nature

The idea that the vacuum energy density [Formula: see text] could be time-dependent is a most reasonable one in the expanding Universe; in fact, much more reasonable than just a rigid cosmological constant for the entire cosmic history. Being [Formula: see text] dynamical, it offers a possibility to tackle the cosmological constant problem in its various facets. Furthermore, for a long time (most prominently since Dirac’s first proposal on a time variable gravitational coupling) the possibility that the fundamental “constants” of Nature are slowly drifting with the cosmic expansion has been continuously investigated. In the last two decades, and specially in recent times, mounting experimental evidence attests that this could be the case. In this paper, we consider the possibility that these two groups of facts might be intimately connected, namely that the observed acceleration of the Universe and the possible time variation of the fundamental constants are two manifestations of the same underlying dynamics. We call it: the “micro and macro connection”, and on its basis we expect that the cosmological term in Einstein’s equations, Newton’s coupling and the masses of all the particles in the Universe, both the dark matter (DM) particles and the ordinary baryons and leptons, should all drift with the cosmic expansion. Here, we discuss specific cosmological models realizing such possibility in a way that preserves the principle of covariance of general relativity (GR).

Cosmological constant

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Vacuum Fluctuations ◽  
Present Epoch ◽  
Modify Gravity ◽  
Expansion Of The Universe ◽  
The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

scholarly journals Chameleon field and the late time acceleration of the Universe

Pramana ◽  
2010 ◽  
Vol 74 (3) ◽  
pp. 481-489 ◽  
Author(s):  
Narayan Banerjee ◽  
Sudipta Das ◽  
Koyel Ganguly
Keyword(s):  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

INFLATION, QUINTESSENCE PROBLEM AND VARYING SPEED OF LIGHT

2002 ◽  
Vol 17 (05) ◽  
pp. 295-302
Author(s):  
SUBENOY CHAKRABORTY
Keyword(s):  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Speed Of Light ◽  
Expansion Of The Universe ◽  
The Universe

In this paper it is shown that the present accelerated expansion of the Universe can be explained only by considering variation of the speed of light, without taking into account the cosmological constant or quintessence matter.

scholarly journals INTERACTION BETWEEN DARK ENERGY AND DARK MATTER: OBSERVATIONAL CONSTRAINTS FROM OHD, BAO, CMB AND SNe Ia

2013 ◽  
Vol 22 (14) ◽  
pp. 1350082 ◽  
Author(s):  
SHUO CAO ◽  
NAN LIANG
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Observational Constraints ◽  
Coincidence Problem ◽  
Cosmological Constraints ◽  
Coincidence Index ◽  
Acceleration Of The Universe ◽  
Interaction Term ◽  
Negative Coupling ◽  
The Universe

In order to test if there is energy transfer between dark energy (DE) and dark matter (DM), we investigate cosmological constraints on two forms of nontrivial interaction between the DM sector and the sector responsible for the acceleration of the universe, in light of the newly revised observations including OHD, CMB, BAO and SNe Ia. More precisely, we find the same tendencies for both phenomenological forms of the interaction term Q = 3γHρ, i.e. the parameter γ to be a small number, |γ| ≈ 10-2. However, concerning the sign of the interaction parameter, we observe that γ > 0 when the interaction between dark sectors is proportional to the energy density of dust matter, whereas the negative coupling (γ < 0) is preferred by observations when the interaction term is proportional to DE density. We further discuss two possible explanations to this incompatibility and apply a quantitative criteria to judge the severity of the coincidence problem. Results suggest that the γm IDE model with a positive coupling may alleviate the coincidence problem, since its coincidence index C is smaller than that for the γd IDE model, the interacting quintessence and phantom models by four orders of magnitude.

scholarly journals ANISOTROPIC COMPACT STARS WITH VARIABLE COSMOLOGICAL CONSTANT

2012 ◽  
Vol 21 (13) ◽  
pp. 1250088 ◽  
Author(s):  
SK. MONOWAR HOSSEIN ◽  
FAROOK RAHAMAN ◽  
JAYANTA NASKAR ◽  
MEHEDI KALAM ◽  
SAIBAL RAY
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Compact Star ◽  
Compact Stars ◽  
Radial Dependence ◽  
Regularity Conditions ◽  
Variable Cosmological Constant ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Surface Redshift

Recently, the small value of the cosmological constant and its ability to accelerate the expansion of the universe is of great interest. We discuss the possibility of forming of anisotropic compact stars from this cosmological constant as one of the competent candidates of dark energy. For this purpose, we consider the analytical solution of Krori and Barua metric. We take the radial dependence of cosmological constant and check all the regularity conditions, TOV equations, stability and surface redshift of the compact stars. It has been shown as conclusion that this model is valid for any compact star and we have cited 4U 1820-30 as a specific example of that kind of star.

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