scholarly journals The GCDM Model

Author(s):  
Martin Reid Johnson

Abstract A model for the reduction in Universal density over time, the “GCDM” model, is derived using gas thermodynamics with z = 1089 as the starting point. In the GCDM model, the Universe is pushing itself apart with internal gas pressure. A simple three-term Hubble expression HG is derived and found to be independent, or zero-order, in temperature and molecular weight of the gas. Isoentropic expansion of the gas at any z yields an entropic energy term which is modified to include energetic electrons, derived in turn from high-energy photons. These electrons are proposed as the source of the “dark energy” term found in the ΛCDM model.

2011 ◽  
Vol 01 ◽  
pp. 228-233
Author(s):  
YUNGUI GONG

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].


2020 ◽  
Vol 2020 ◽  
pp. 1-11 ◽  
Author(s):  
Tom F. Neiser

When the Large Hadron Collider resumes operations in 2021, several experiments will directly measure the motion of antihydrogen in free fall for the first time. Our current understanding of the universe is not yet fully prepared for the possibility that antimatter has negative gravitational mass. This paper proposes a model of cosmology, where the state of high energy density of the big bang is created by the collapse of an antineutrino star that has exceeded its Chandrasekhar limit. To allow the first neutrino stars and antineutrino stars to form naturally from an initial quantum vacuum state, it helps to assume that antimatter has negative gravitational mass. This assumption may also be helpful to identify dark energy. The degenerate remnant of an antineutrino star can today have an average mass density that is similar to the dark energy density of the ΛCDM model. When in hydrostatic equilibrium, this antineutrino star remnant can emit isothermal cosmic microwave background radiation and accelerate matter radially. This model and the ΛCDM model are in similar quantitative agreement with supernova distance measurements. Therefore, this model is useful as a purely academic exercise and as preparation for possible future discoveries.


2009 ◽  
Vol 18 (05) ◽  
pp. 865-887
Author(s):  
S. K. SRIVASTAVA ◽  
J. DUTTA

In this paper, the cosmology of the late and future universe is obtained from f(R) gravity with nonlinear curvature terms R2 and R3 (R is the Ricci scalar curvature). It is different from f(R) dark energy models where nonlinear curvature terms are taken as a gravitational alternative to dark energy. In the present model, neither linear nor nonlinear curvature terms are taken as dark energy. Rather, dark energy terms are induced by curvature terms and appear in the Friedmann equation derived from f(R) gravitational equations. This approach has an advantage over f(R) dark energy models in three ways: (i) results are consistent with WMAP observations, (ii) dark matter is produced from the gravitational sector and (iii) the universe expands as ~ t2/3 during dominance of the curvature-induced dark matter, which is consistent with the standard cosmology. Curvature-induced dark energy mimics phantom and causes late acceleration. It is found that transition from matter-driven deceleration to acceleration takes place at the redshift 0.36 at time 0.59 t0 (t0 is the present age of the universe). Different phases of this model, including acceleration and deceleration during the phantom phase, are investigated. It is found that expansion of the universe will stop at the age of 3.87 t0 + 694.4 kyr. After this epoch, the universe will contract and collapse by the time of 336.87 t0 + 694.4 kyr. Further, it is shown that cosmic collapse obtained from classical mechanics can be avoided by making quantum gravity corrections relevant near the collapse time due to extremely high energy density and large curvature analogous to the state of the very early universe. Interestingly, the cosmological constant is also induced here; it is extremely small in the classical domain but becomes very high in the quantum domain. This result explains the largeness of the cosmological constant in the early universe due to quantum gravity effects during this era and its very low value in the present universe due to negligible quantum effect in the late universe.


2014 ◽  
Vol 11 (02) ◽  
pp. 1460014 ◽  
Author(s):  
Winfried Zimdahl

Interactions inside the cosmological dark sector influence the cosmological dynamics. As a consequence, the future evolution of the Universe may be different from that predicted by the ΛCDM model. We review main features of several recently studied models with nongravitational couplings between dark matter and dark energy.


2014 ◽  
Vol 10 (S306) ◽  
pp. 54-56
Author(s):  
Simone Aiola ◽  
Arthur Kosowsky ◽  
Bingjie Wang

AbstractThe integrated Sachs-Wolfe effect was recently detected at a level of 4.4σ by [Granett et al. (2008)], by stacking compensated CMB temperature patches corresponding to superstructures in the universe. We test the reported signal using realistic gaussian random realizations of the CMB sky, based on the temperature power spectrum predicted by the concordance ΛCDM model. Such simulations provide a complementary approach to the largely used N-body simulations and allow to include the contaminant effects due to small-scale temperature fluctuations. We also apply our pipeline to foreground-cleaned CMB sky maps using the [Granett et al. (2008)] voids/clusters catalog. We confirm the detection of a signal, which depart from the null hypothesis by 3.5σ, and we report a tension with our theoretical estimates at a significance of about 2.5σ.


2004 ◽  
Vol 13 (04) ◽  
pp. 669-693 ◽  
Author(s):  
R. COLISTETE ◽  
J. C. FABRIS ◽  
S. V. B. GONÇALVES ◽  
P. E. DE SOUZA

The type Ia supernovae observational data are used to estimate the parameters of a cosmological model with cold dark matter and the Chaplygin gas. This exotic gas, which is characterized by a negative pressure varying with the inverse of density, represents in this model the dark energy responsible for the acceleration of the Universe. The Chaplygin gas model depends essentially on four parameters: the Hubble constant, the velocity of the sound of the Chaplygin gas, the curvature of the Universe and the fraction density of the Chaplygin gas and the cold dark matter. The Bayesian parameter estimation yields [Formula: see text] and [Formula: see text]. These and other results indicate that a Universe completely dominated by the Chaplygin gas is favoured, what reinforces the idea that the Chaplygin gas may unify the description for dark matter and dark energy, at least as the type Ia supernovae data are concerned. A closed and accelerating Universe is also favoured. The Bayesian statistics indicates that the Chaplygin gas model is more likely than the standard cosmological constant (ΛCDM) model at 55.3% confidence level when an integration on all free parameters is performed. Assuming the spatially flat curvature, this percentage mounts to 65.3%. On the other hand, if the density of dark matter is fixed at zero value, the Chaplygin gas model becomes more preferred than the ΛCDM model at 91.8% confidence level. Finally, the hypothesis of flat Universe and baryonic matter (Ωb0=0.04) implies a Chaplygin gas model preferred over the ΛCDM at a confidence level of 99.4%.


2011 ◽  
Vol 20 (07) ◽  
pp. 1235-1249 ◽  
Author(s):  
SUDIPTA DAS ◽  
SUBIR GHOSH ◽  
JAN-WILLEM VAN HOLTEN ◽  
SUPRATIK PAL

We consider the generalized particle dynamics, that we proposed [S. Das et al., J. High. Energy Phys.0904 (2009) 115] in braneworld formalisms for an asymptotically anti-de Sitter background. The present framework results in a new model that accounts for the late acceleration of the universe. An effective dark energy equation of state, exhibiting a phantom-like behavior, is generated. The model is derived by embedding the physical FLRW universe in a (4 + 1)-dimensional effective spacetime, induced by the generalized particle dynamics. We corroborate our results with present-day observed cosmological parameters.


2021 ◽  
Author(s):  
◽  
Brett Innes Davidson

<p>This thesis proposes a critical framework by which science fiction can be read as an indicator of significant trends and debates in science and culture. It takes as its starting point Brian Aldiss's statement that science fiction's purpose is to articulate in fictional form a definition of humanity and its status in the universe that will stand in the light of science. Science fiction exists as a means by which scientific concepts are constructed as cultural interpretations, and as both have changed significantly over the period from the emergence of the genre in the mid nineteenth century through the twentieth century, analysis of science-fictional forms and practices can reveal the processes of their evolution. A critical framework is constructed based on Aldiss' definition, identifying first, a construction of selfhood and spatiality - physical and metaphysical - as being fundamental, and secondly, identifying the emergence and evolution of major 'Orders' that take different approaches to key issues and which engage with each other both antagonistically and creatively. The thesis begins with an investigation of the cultural construction of space and then covers the emergence of science fiction as it relates to the project to define humanity and its standing in the universe in a manner consistent with science. Three Orders and their emergence are then described according to their architectonic schemae and their epistemological and creative processes. The first is the Modernist Order, based on Cartesian spatiality and mind-body dualism and empirical scientific practice. The second, which emerged as an attempt to synthesise modern science with traditional culture, is the Neohumanist Order. The third, still very much in flux, is the Posthumanist Order, which is very much inspired both by postmodernism and cybernetics. The three following chapters deal with the Orders in turn, selecting exemplary texts from their emergent and developed (or developing) stages, suggesting also the points in the development of each where another Order has disengaged and emerged in its own right. Because science and culture evolve over time, examination of the Orders is intrinsically linked to a concept of science fiction as being an ongoing discourse, each selected text is interpreted as being a response to a particular issue at a particular cultural moment, but nonetheless connected to predecessor and successor texts that represent a line of argument pursued over time within and between Orders. The Orders are not hermetic by any means, and their most enlightening aspects can be their varying treatment of a common concept. The cyborg furnishes an excellent example, being treated differently by each of the Orders as it is an image of the integration of humanity and technology. Issues such as self, body, boundary, location, the other and communication are all represented in the cyborg and the next two chapters discuss the cyborg as treated by different Orders, in the first case, as a body and in the second case, as an inhabitant and creation of architectonics and culture. The conclusion then discusses the current state of affairs regarding the system of Orders as a critical method. It is shown that 'impure' texts that contain aspects of each of the Orders do not negate their usefulness, but rather demonstrate it as texts (and postmodern texts in particular) provide stages on which the Orders can be displayed engaging with each other.</p>


2021 ◽  
Vol 66 (9) ◽  
pp. 739
Author(s):  
S.L. Parnovsky

The tensions concerning the values of Hubble constant obtained from the early and the late Universe data pose a significant challenge to modern cosmology. Possible modifications of the flat homogeneous isotropic cosmological ΛCDM model are considered, in which the Universe contains the dark energy, cold baryonic matter, and dark matter. They are based on general relativity and satisfy two requirements: (1) the value of the Hubble constant calculated from the value of the Hubble parameter at the recombination by formulas of the flat ΛCDM model, should be equal to 92% of the one based on low-redshift observations; (2) deviations from the ΛCDM model should not lead to effects that contradict astronomical observations and estimations obtained thereof. The analysis showed that there are few opportunities for the choice. Either we should consider DM with negative pressure −pdmc2 ≪ pdm < 0, which weakly affects the evolution of the Universe and the observed manifestations of DM, or we should admit the mechanism of generation of new matter, for example, by the dark energy decay.


Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 11 ◽  
Author(s):  
Matthew J. Lake

We introduce a dark energy-modified minimum length uncertainty relation (DE-MLUR) or dark energy uncertainty principle (DE-UP) for short. The new relation is structurally similar to the MLUR introduced by Károlyházy (1968), and reproduced by Ng and van Dam (1994) using alternative arguments, but with a number of important differences. These include a dependence on the de Sitter horizon, which may be expressed in terms of the cosmological constant as l dS ∼ 1 / Λ . Applying the DE-UP to both charged and neutral particles, we obtain estimates of two limiting mass scales, expressed in terms of the fundamental constants G , c , ℏ , Λ , e . Evaluated numerically, the charged particle limit corresponds to the order of magnitude value of the electron mass ( m e ), while the neutral particle limit is consistent with current experimental bounds on the mass of the electron neutrino ( m ν e ). Possible cosmological consequences of the DE-UP are considered and we note that these lead naturally to a holographic relation between the bulk and the boundary of the Universe. Low and high energy regimes in which dark energy effects may dominate canonical quantum behaviour are identified and the possibility of testing the model using near-future experiments is briefly discussed.


Sign in / Sign up

Export Citation Format

Share Document