scholarly journals Dark Energy and Cosmological Constant

2018 ◽  
Vol 17 (1) ◽  
pp. 25-32
Author(s):  
Louise Rebecca ◽  
C Sivaram ◽  
Kenath Arun
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Mass Density ◽  
Critical Density ◽  
Accelerated Expansion ◽  
Microwave Background ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Ia Supernovae ◽  
The Universe

One of the unresolved problems in cosmology is that the measured mass density of the universe has revealed a value that was about 30% of the critical density. Since the universe is very nearly spatially flat, as is indicated by measurements of the cosmic microwave background, about 70% of the energy density of the universe was left unaccounted for. Another observation seems to be connected to this mystery. Generally one would expect the rate of expansion to slow down once the universe started expanding. The measurements of Type Ia supernovae have revealed that the expansion of the universe is actually accelerating. This accelerated expansion is attributed to the so-called dark energy (DE).Here we give a brief overview on the observational basis for DE hypothesis and how cosmological constant, initially proposed by Einstein to obtain a static universe, can play the role of dark energy.

scholarly journals “Pure” Supernovae and Dark Energy

2011 ◽  
Vol 7 (S281) ◽  
pp. 17-20
Author(s):  
M. V. Pruzhinskaya ◽  
E. S. Gorbovskoy ◽  
V. M. Lipunov
Keyword(s):  
Dark Energy ◽  
Chemical Evolution ◽  
Special Class ◽  
Accelerated Expansion ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Ia Supernovae ◽  
The Universe

AbstractA special class of Type Ia supernovae that is not subject to ordinary and additional intragalactic gray absorption and chemical evolution has been identified. Analysis of the Hubble diagrams constructed for these supernovae confirms the accelerated expansion of the Universe irrespective of the chemical evolution and possible gray absorption in galaxies.

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 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.

scholarly journals "Doppler De-boosting" and the Observation of "Standard Candles" in Cosmology

2021 ◽  
Author(s):  
Mark Zilberman ◽  
Keyword(s):  
Dark Energy ◽  
Relativistic Effect ◽  
Accelerated Expansion ◽  
Light Sources ◽  
Relativistic Jets ◽  
Radiation Sources ◽  
Standard Candle ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

“Doppler boosting” is a well-known relativistic effect that alters the apparent luminosity of approaching radiation sources. “Doppler de-boosting” is the same relativistic effect observed but for receding light sources (e.g. relativistic jets of AGN and GRB). “Doppler boosting” alters the apparent luminosity of approaching light sources to appear brighter, while “Doppler de-boosting” alters the apparent luminosity of receding light sources to appear fainter. While “Doppler de-boosting” has been successfully accounted for and observed in relativistic jets of AGN, it was ignored in the establishment of Standard candles for cosmological distances. A Standard Candle adjustment of Z>0.1 is necessary for “Doppler de-boosting”, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of “Doppler de-boosting” but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of the redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)α -3 and for Type Ia supernova appears as ℳ(Z) = L/Lo=(Z+1)-2. “Doppler de-boosting” may also explain the anomalously low luminosity of objects with a high Z without the introduction of an accelerated expansion of the Universe and Dark Energy.

scholarly journals ANISOTROPIC DARK ENERGY AND ELLIPSOIDAL UNIVERSE

2011 ◽  
Vol 20 (06) ◽  
pp. 1153-1166 ◽  
Author(s):  
L. CAMPANELLI ◽  
P. CEA ◽  
G. L. FOGLI ◽  
L. TEDESCO
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
Background Radiation ◽  
Microwave Background ◽  
Anisotropic Dark Energy ◽  
Large Scale Geometry ◽  
Microwave Background Radiation ◽  
Type Ia ◽  
Ia Supernovae ◽  
The Universe

A cosmological model with anisotropic dark energy is analyzed. The amount of deviation from isotropy of the equation of state of dark energy, the skewness δ, generates an anisotropization of the large-scale geometry of the Universe, quantifiable by means of the actual shear Σ0. Requiring that the level of cosmic anisotropization at the time of decoupling be such that we can solve the "quadrupole problem" of cosmic microwave background radiation, we find that |δ| ~ 10-4 and |Σ_0| ~10-5, compatible with existing limits derived from the magnitude redshift data on Type Ia supernovae.

scholarly journals FITTING THE LUMINOSITY DATA FROM TYPE Ia SUPERNOVAE IN THE FRAME OF THE COSMIC DEFECT THEORY

2009 ◽  
Vol 18 (03) ◽  
pp. 501-512
Author(s):  
A. TARTAGLIA ◽  
M. CAPONE ◽  
V. CARDONE ◽  
N. RADICELLA
Keyword(s):  
Accelerated Expansion ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The One ◽  
Ia Supernovae ◽  
The Universe ◽  
Good Agreement

The cosmic defect (CD) theory is reviewed and used to fit the data for the accelerated expansion of the universe, obtained from the apparent luminosity of 192 SnIa 's. The fit from the CD theory is compared with the one obtained by means of ΛCDM. The results from the two theories are in good agreement and the fits are satisfactory. The correspondence between the two approaches is discussed and interpreted.

The Mystery of the Dark Energy Based on Energy Materials

2012 ◽  
Vol 496 ◽  
pp. 523-526
Author(s):  
Jian Guo Lu ◽  
Ming Hu
Keyword(s):  
Dark Energy ◽  
Gamma Ray ◽  
Background Radiation ◽  
Accelerated Expansion ◽  
Energy Materials ◽  
Type Ia Supernova ◽  
Microwave Background Radiation ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

Recently the observations on the type Ia supernova has showed the accelerated expansion of the universe which can be used to illustrate by the “dark energy”. In order to understand the accelerated expansion of the universe and the dark energy, people study them based on two aspects: theoretical mechanism and cosmology observation restrictions. The simplest and the most frequently used models of the dark energy are the vacuum energy, cosmic constant model and quintessence model etc. The measurement of the universe can be used to identify the properties of the dark energy. The anisotropy of the type Ia supernova and cosmic microwave background radiation are the methods which commonly used to detect the dark energy, other methods are weak lensing, X ray gas group, high red shift gamma-ray burst and so on

scholarly journals Testing dissipative dark matter in causal thermodynamics

2020 ◽  
pp. 2150032
Author(s):  
Norman Cruz ◽  
Esteban González ◽  
Guillermo Palma
Keyword(s):  
Dark Matter ◽  
Accelerated Expansion ◽  
Model Parameters ◽  
Fitted Parameter ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Viscous Pressure ◽  
Ia Supernovae ◽  
Parameter Values ◽  
The Universe

In this paper we study the consistency of a cosmological model representing a universe filled with a one-component dissipative dark matter fluid, in the framework of the causal Israel–Stewart theory, where a general expression arising from perturbation analysis for the relaxation time [Formula: see text] is used. This model is described by an exact analytic solution recently found in [N. Cruz, E. González and G. Palma, Gen. Relat. Gravit. 52, 62 (2020), which depends on several model parameters as well as integration constants, allowing the use of Type Ia Supernovae and Observational Hubble data to perform by an astringent observational tests. The constraint regions found for the parameters of the solution allow the existence of an accelerated expansion of the universe at late times, after the domination era of the viscous pressure, which holds without the need of including a cosmological constant. Nevertheless, the fitted parameter values lead to drawbacks as a very large non-adiabatic contribution to the speed of sound, and some inconsistencies, not totally conclusive, with the description of the dissipative dark matter as a fluid, which is nevertheless a common feature of these kind of models.

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 Geodesics and bending of light around a BTZ black hole surrounded by quintessential matter

2021 ◽  
Author(s):  
Shubham Kala ◽  
Hemwati Nandan ◽  
Prateek Sharma ◽  
Maye Elmardi
Keyword(s):  
Black Hole ◽  
Dark Energy ◽  
Background Radiation ◽  
Accelerated Expansion ◽  
Acoustic Oscillations ◽  
Btz Black Hole ◽  
Microwave Background ◽  
Microwave Background Radiation ◽  
Type Ia ◽  
Expansion Of The Universe

Various observations from cosmic microwave background radiation (CMBR), type Ia supernova and baryon acoustic oscillations (BAO) are strongly suggestive of an accelerated expansion of the universe which can be explained by the presence of mysterious energy known as dark energy. The quintessential matter coupled with gravity minimally is considered one of the possible candidates to represent the presence of such dark energy in our universe. In view of this scenario, we study the geodesic of massless particles as well as massive particles around a (2 + 1)-dimensional BTZ black hole (BH) spacetime surrounded by the quintessence. The effect of parameters involved in the deflection of light by such a BH spacetime is investigated in detail. The results obtained are then compared with a usual non-rotating BTZ BH spacetime.

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