Phenomenological modification of horizon temperature

In this paper, a study of the accelerated expansion problem of the large scale universe is presented. To derive Friedmann like equations, describing the background dynamics of the recent universe, we take into account, that it is possible to interpret the spacetime dynamics as an emergent phenomenon. It is a consequence of the deep study of connection between gravitation and thermodynamics. The models considered are based on phenomenological modifications of the horizon temperature. In general, there are various reasons to modify the horizon temperature, one of which is related to the feedback from the spacetime on the horizon, generating additional heat. In order to constrain the parameters of the models, we use Om analysis and the constraints on this parameter at z = 0.0, z = 0.57 and z = 2.34.

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A varying polytropic gas universe and phase space analysis

Modern Physics Letters A ◽

10.1142/s0217732316500978 ◽

2016 ◽

Vol 31 (16) ◽

pp. 1650097 ◽

Cited By ~ 10

Author(s):

M. Khurshudyan

Keyword(s):

Phase Space ◽

Large Scale ◽

Accelerated Expansion ◽

Late Time ◽

Mathematical Tool ◽

Phase Space Analysis ◽

Space Analysis ◽

Polytropic Gas ◽

Dark Fluid ◽

Large Scale Universe

In this paper, we will consider a phenomenological model of a dark fluid that is able to explain an accelerated expansion of our low redshift universe and the phase transition to this accelerated expanding universe. Recent developments in modern cosmology towards understanding of the accelerated expansion of the large scale universe involve various scenarios and approaches. Among these approaches, one of well-known and accepted practice is modeling of the content of our universe via dark fluid. There are various models of dark energy fluid actively studied in recent literature and polytropic gas is among them. In this work, we will consider a varying polytropic gas which is a phenomenological modification of polytropic gas. Our model of varying polytropic dark fluid has been constructed to analogue to a varying Chaplygin gas actively discussed in the literature. We will consider interacting models, where dark matter is a pressureless fluid, to have a comprehensive picture. Phase space analysis is an elegant mathematical tool to earn general understanding of large scale universe and easily see an existence of a solution to cosmological coincidence problem. Imposing some constraints on parameters of the models, we found late time attractors for each case analytically. Cosmological consequences for the obtained late time attractors are discussed.

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Interacting dark energy models in f(T) gravity

Modern Physics Letters A ◽

10.1142/s0217732317500973 ◽

2017 ◽

Vol 32 (18) ◽

pp. 1750097 ◽

Cited By ~ 1

Author(s):

M. Khurshudyan ◽

R. Myrzakulov ◽

As. Khurshudyan

Keyword(s):

Phase Transition ◽

Observational Data ◽

Large Scale ◽

Cosmological Models ◽

Accelerated Expansion ◽

Late Time ◽

Time Behavior ◽

Expanding Universe ◽

Theory Of Gravity ◽

Large Scale Universe

The accelerated expansion of the large-scale universe can be explained in various ways. There are various modifications, and each of them makes an attempt to give its own explanation of the physics behind it. It is well known that modern cosmology is full of various phenomenological assumptions to obtain comprehensive results comparable with observational data. General Relativity is the main theory of gravity and proposed modifications compared to it, giving a hope to find explanations of phenomenological assumptions. f(T) theory of gravity is one of the options. In this paper, we will consider a particular example of f(T) theory and study the effects of various interactions on a cosmological model. Phase space analysis is used to have a qualitative understanding of the late-time behavior of the suggested cosmological models. During our study, we found that among phenomenological models suggested in this paper, we have cosmological models being in good agreement with the observational data. Moreover, study of the behavior of the deceleration parameter q showed a phase transition from a decelerated expanding universe to the accelerated (recent) expanding universe. On the other hand, for the parameters of the models giving the mentioned phase transition, we have estimated the present day values of statefinder parameters (r, s).

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On cosmology of interacting varying polytropic dark fluids

Modern Physics Letters A ◽

10.1142/s0217732319501335 ◽

2019 ◽

Vol 34 (17) ◽

pp. 1950133

Author(s):

Martiros Khurshudyan ◽

Asatur Khurshudyan

Keyword(s):

Dark Matter ◽

Gravitational Lensing ◽

Large Scale ◽

Cold Dark Matter ◽

Accelerated Expansion ◽

Dark Side ◽

Model Parameters ◽

Special Role ◽

Large Scale Universe

In this paper, a possibility of the accelerated expansion of the large scale universe with interacting varying polytropic fluid of a certain type is presented. About a special role of non-gravitational interactions between dark energy and dark matter, in particular, about a possibility of improvement and solution of problems arising in modern cosmology, has been discussed for a long time. This motivates us to consider new models, where non-gravitational interactions between varying polytropic fluid and cold dark matter are allowed. Mainly nonlinear interactions of a specific type is considered, found in recent literature. The present study extends previously obtained results demonstrating that considered new parameterization of dark side of the universe could be supported by available observational data and will present the role of considered non-gravitational interactions in this case. During the study of suggested cosmological models Om analysis is applied. Moreover, with different datasets, including a strong gravitational lensing dataset, the best fit values of the model parameters are obtained using [Formula: see text] analysis.

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FORMATION OF DARK MATTER HALOES IN A HOMOGENEOUS DARK ENERGY UNIVERSE

International Journal of Modern Physics D ◽

10.1142/s0218271810017561 ◽

2010 ◽

Vol 19 (08n10) ◽

pp. 1397-1403

Author(s):

L. MARASSI

Keyword(s):

Dark Matter ◽

Dark Energy ◽

Large Scale ◽

State Parameter ◽

Mass Function ◽

Accelerated Expansion ◽

X Ray ◽

Energy Models ◽

Dark Energy Component ◽

Standard Press

Several independent cosmological tests have shown evidences that the energy density of the universe is dominated by a dark energy component, which causes the present accelerated expansion. The large scale structure formation can be used to probe dark energy models, and the mass function of dark matter haloes is one of the best statistical tools to perform this study. We present here a statistical analysis of mass functions of galaxies under a homogeneous dark energy model, proposed in the work of Percival (2005), using an observational flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our analysis, the standard Press–Schechter (PS) approach (where a Gaussian distribution is used to describe the primordial density fluctuation field of the mass function), and the PL (power–law) mass function (where we apply a non-extensive q-statistical distribution to the primordial density field). We conclude that the PS mass function cannot explain at the same time the X-ray and the CMB data (even at 99% confidence level), and the PS best fit dark energy equation of state parameter is ω = -0.58, which is distant from the cosmological constant case. The PL mass function provides better fits to the HIFLUGCS X-ray galaxy data and the CMB data; we also note that the ω parameter is very sensible to modifications in the PL free parameter, q, suggesting that the PL mass function could be a powerful tool to constrain dark energy models.

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Dark energy with zero pressure: Accelerated expansion and large scale structure in action-dependent Lagrangian theories

Physical Review D ◽

10.1103/physrevd.98.103501 ◽

2018 ◽

Vol 98 (10) ◽

Cited By ~ 2

Author(s):

Thiago R. P. Caramês ◽

H. Velten ◽

J. C. Fabris ◽

Matheus J. Lazo

Keyword(s):

Dark Energy ◽

Large Scale ◽

Large Scale Structure ◽

Scale Structure ◽

Accelerated Expansion

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Do supernovae indicate an accelerating universe?

The European Physical Journal Special Topics ◽

10.1140/epjs/s11734-021-00199-6 ◽

2021 ◽

Author(s):

Roya Mohayaee ◽

Mohamed Rameez ◽

Subir Sarkar

Keyword(s):

Dark Energy ◽

Large Scale ◽

Bulk Flow ◽

Expansion Rate ◽

Accelerated Expansion ◽

Accelerating Universe ◽

Acoustic Oscillations ◽

Independent Evidence ◽

Peculiar Velocity ◽

Hubble Expansion

AbstractIn the late 1990’s, observations of two directionally-skewed samples of, in total, 93 Type Ia supernovae were analysed in the framework of the Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology. Assuming these to be ‘standard(isable) candles’ it was inferred that the Hubble expansion rate is accelerating as if driven by a positive Cosmological Constant $$\varLambda $$ Λ in Einstein’s theory of gravity. This is still the only direct evidence for the ‘dark energy’ that is the dominant component of today’s standard $$\varLambda $$ Λ CDM cosmological model. Other data such as baryon acoustic oscillations (BAO) in the large-scale distribution of galaxies, temperature fluctuations in the cosmic microwave background (CMB), measurement of stellar ages, the rate of growth of structure, etc are all ‘concordant’ with this model but do not provide independent evidence for accelerated expansion. The recent discussions about whether the inferred acceleration is real rests on analysis of a larger sample of 740 SNe Ia which shows that these are not quite standard candles, and more importantly highlights the ‘corrections’ that are applied to analyse the data in the FLRW framework. The latter holds in the reference frame in which the CMB is isotropic, whereas observations are carried out in our heliocentric frame in which the CMB has a large dipole anisotropy. This is assumed to be of kinematic origin i.e. due to our non-Hubble motion driven by local inhomogeneity in the matter distribution which has grown under gravity from primordial density perturbations traced by the CMB fluctuations. The $$\varLambda $$ Λ CDM model predicts how this peculiar velocity should fall off as the averaging scale is raised and the universe becomes sensibly homogeneous. However observations of the local ‘bulk flow’ are inconsistent with this expectation and convergence to the CMB frame is not seen. Moreover, the kinematic interpretation implies a corresponding dipole in the sky distribution of high redshift quasars, which is rejected by observations at $$4.9\sigma $$ 4.9 σ . Hence the peculiar velocity corrections employed in supernova cosmology are inconsistent and discontinuous within the data. The acceleration of the Hubble expansion rate is in fact anisotropic at $$3.9\sigma $$ 3.9 σ and aligned with the bulk flow. Thus dark energy could be an artefact of analysing data assuming that we are idealised observers in an FLRW universe, when in fact the real universe is inhomogeneous and anisotropic out to distances large enough to impact on cosmological analyses.

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Using Unreal Engine to Visualize a Cosmological Volume

Universe ◽

10.3390/universe6100168 ◽

2020 ◽

Vol 6 (10) ◽

pp. 168

Author(s):

Christopher Marsden ◽

Francesco Shankar

Keyword(s):

Real Time ◽

Large Scale ◽

Graphics Processing Unit ◽

Large Scale Structure ◽

Two Dimensions ◽

Scale Structure ◽

Sloan Digital Sky Survey ◽

Processing Unit ◽

Large Scale Universe ◽

Time Projection

In this work we present “Astera’’, a cosmological visualization tool that renders a mock universe in real time using Unreal Engine 4. The large scale structure of the cosmic web is hard to visualize in two dimensions, and a 3D real time projection of this distribution allows for an unprecedented view of the large scale universe, with visually accurate galaxies placed in a dynamic 3D world. The underlying data are based on empirical relations assigned using results from N-Body dark matter simulations, and are matched to galaxies with similar morphologies and sizes, images of which are extracted from the Sloan Digital Sky Survey. Within Unreal Engine 4, galaxy images are transformed into textures and dynamic materials (with appropriate transparency) that are applied to static mesh objects with appropriate sizes and locations. To ensure excellent performance, these static meshes are “instanced’’ to utilize the full capabilities of a graphics processing unit. Additional components include a dynamic system for representing accelerated-time active galactic nuclei. The end result is a visually realistic large scale universe that can be explored by a user in real time, with accurate large scale structure. Astera is not yet ready for public release, but we are exploring options to make different versions of the code available for both research and outreach applications.

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Hubble flow variations as a test for inhomogeneous cosmology

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629174 ◽

2019 ◽

Vol 622 ◽

pp. A83 ◽

Cited By ~ 1

Author(s):

Christoph Saulder ◽

Steffen Mieske ◽

Eelco van Kampen ◽

Werner W. Zeilinger

Keyword(s):

Large Scale ◽

Cold Dark Matter ◽

Statistical Tests ◽

Specific Model ◽

Accelerated Expansion ◽

Inhomogeneous Cosmology ◽

Galaxy Surveys ◽

Model Versus ◽

Differential Expansion ◽

Hubble Flow

Context. Backreactions from large-scale inhomogeneities may provide an elegant explanation for the observed accelerated expansion of the universe without the need to introduce dark energy. Aims. We propose a cosmological test for a specific model of inhomogeneous cosmology, called timescape cosmology. Using large-scale galaxy surveys such as SDSS and 2MRS, we test the variation of expansion expected in the Λ-cold dark matter (Λ-CDM) model versus a more generic differential expansion using our own calibrations of bounds suggested by timescape cosmology. Methods. Our test measures the systematic variations of the Hubble flow towards distant galaxies groups as a function of the matter distribution in the lines of sight to those galaxy groups. We compare the observed systematic variation of the Hubble flow to mock catalogues from the Millennium Simulation in the case of the Λ-CDM model, and a deformed version of the same simulation that exhibits more pronounced differential expansion. Results. We perform a series of statistical tests, ranging from linear regressions to Kolmogorov-Smirnov tests, on the obtained data. They consistently yield results preferring Λ-CDM cosmology over our approximated model of timescape cosmology. Conclusions. Our analysis of observational data shows no evidence that the variation of expansion differs from that of the standard Λ-CDM model.

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