Dark Cosmology: Shedding Light on Our Current Universe

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 12694

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Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, AP 70543, Ciudad de México 04510, Mexico
Interests: general relativity; cosmology; thermodynamics; relativistic astrophysics
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Special Issue Information

Dear Colleagues,

The current understanding of the universe expansion history is based on the six-parameters minimal ΛCDM model. Although appealing and well-consolidated for its experimental guidance, the model shows strong discrepancies between quantum expectations and cosmic observations. Cosmologists believe that the ΛCDM model could be incomplete, even because the dark contributions (dark energy and dark matter) are dominant and drive the universe dynamics. If the ΛCDM model is not the final paradigm of the whole dynamics, which extensions or modifications are expected to reproduce cosmic data?

Even though alternative paradigms, spanning from barotropic dark energy models up to extended theories of gravity, have been widely explored, recent Planck observations confirm that the ΛCDM model is the best candidate for describing the large-scale universe. However, inflation seems to be modeled by means of the simplest correction to the Einstein–Hilbert action, i.e., the Starobinsky inflationary paradigm. In other words, a complete and self-consistent final paradigm to describe the universe has not so far been formulated and likely should unify the late-time acceleration with all previous cosmic phases, e.g., inflation, reheating, baryogenesis, and so forth.

The main purpose of this Special Issue is to face the idea of “dark cosmology” by proposing alternative treatments to the ΛCDM model, which relate theoretical considerations with observations; in other words, alternative scenarios which consider Λ as interchangeable with other possibilities, passing through phenomenological dark energy constructions, up to alternative frameworks based on modified gravity. Although we embrace several scenarios, which consider different epochs of the universe’s evolution, we strongly encourage those works which make use of observations and numerical constraints. Therefore, we warmly welcome manuscripts based on the interplay between theory and experiments in subjects like dark energy, dark matter, small perturbations, early time cosmology, quantum gravity, extended theories of gravity, etc.

Dr. Orlando Luongo
Dr. Hernando Quevedo
Guest Editors

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Keywords

  • dark energy
  • dark matter
  • inflation
  • missing baryon problem
  • extended theories of gravity

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Published Papers (5 papers)

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20 pages, 984 KiB  
Article
A Mass Dependent Density Profile from Dwarfs to Clusters
by Antonino Del Popolo and Morgan Le Delliou
Galaxies 2022, 10(3), 69; https://doi.org/10.3390/galaxies10030069 - 18 May 2022
Viewed by 2046
Abstract
In this paper, we extend the work of Freundlich et al. 2020 who showed how to obtain a Dekel–Zhao density profile with mass dependent shape parameters in the case of galaxies. In the case of Freundlich et al. 2020, the baryonic dependence was [...] Read more.
In this paper, we extend the work of Freundlich et al. 2020 who showed how to obtain a Dekel–Zhao density profile with mass dependent shape parameters in the case of galaxies. In the case of Freundlich et al. 2020, the baryonic dependence was obtained using the NIHAO set of simulations. In our case, we used simulations based on a model of ours. Following Freundlich et al. 2020, we obtained the dependence from baryon physics of the two shape parameters, obtaining in this way a mass dependent Dekel–Zhao profile describing the dark matter profiles from galaxies to clusters of galaxies. The extension to the Dekel–Zhao mass dependent profile to clusters of galaxies is the main result of the paper. In the paper, we show how the Dekel–Zhao mass dependent profile gives a good description of the density profiles of galaxies, already shown by Freundlich et al. 2020, but also to a set of clusters of galaxies. Full article
(This article belongs to the Special Issue Dark Cosmology: Shedding Light on Our Current Universe)
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6 pages, 243 KiB  
Article
Weyl Conformal Symmetry Model of the Dark Galactic Halo
by R. K. Nesbet
Galaxies 2022, 10(2), 49; https://doi.org/10.3390/galaxies10020049 - 15 Mar 2022
Viewed by 1898
Abstract
The postulate of universal conformal (local Weyl scaling) symmetry modifies both general relativity and the Higgs scalar field model. The conformal Higgs model (CHM) generates an effective cosmological constant that fits the observed accelerating Hubble expansion for redshifts z1 (7.33 Gyr) [...] Read more.
The postulate of universal conformal (local Weyl scaling) symmetry modifies both general relativity and the Higgs scalar field model. The conformal Higgs model (CHM) generates an effective cosmological constant that fits the observed accelerating Hubble expansion for redshifts z1 (7.33 Gyr) accurately with only one free parameter. Growth of a galaxy is modeled by the central accumulation of matter from an enclosing empty spherical halo whose radius expands with depletion. Details of this process account for the nonclassical, radial centripetal acceleration observed at excessive orbital velocities in galactic haloes. There is no need for dark matter. Full article
(This article belongs to the Special Issue Dark Cosmology: Shedding Light on Our Current Universe)
10 pages, 846 KiB  
Article
Testing Noncommutativity-Like Model as a Galactic Density Profile
by Juan Jordi Ancona-Flores, Alberto Hernández-Almada and Miguel Angel García-Aspeitia
Galaxies 2021, 9(1), 17; https://doi.org/10.3390/galaxies9010017 - 8 Mar 2021
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Abstract
Noncommutative-like model (NC-like) is an interesting alternative inspired by string theory to understand and describe the velocity rotation curves of galaxies without the inclusion of dark matter particles. In a natural way, a Gaussian density profile emerges and is characterized by a parameter [...] Read more.
Noncommutative-like model (NC-like) is an interesting alternative inspired by string theory to understand and describe the velocity rotation curves of galaxies without the inclusion of dark matter particles. In a natural way, a Gaussian density profile emerges and is characterized by a parameter θ, called the NC-like parameter. Hence we aim to confront the NC-like model with a galaxy sample of the Spitzer Photometry and Accurate Rotation Curves (SPARC) catalog to constrain the model parameters and compare statistically with the Einasto density profile using the Akaike and Bayesian information criteria. According to our results, some galaxies prefer the NC-like over the Einasto model while others do not support NC-like. Full article
(This article belongs to the Special Issue Dark Cosmology: Shedding Light on Our Current Universe)
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13 pages, 697 KiB  
Article
Imprint of Pressure on Characteristic Dark Matter Profiles: The Case of ESO0140040
by Kuantay Boshkayev, Talgar Konysbayev, Ergali Kurmanov, Orlando Luongo and Marco Muccino
Galaxies 2020, 8(4), 74; https://doi.org/10.3390/galaxies8040074 - 22 Oct 2020
Cited by 8 | Viewed by 3419
Abstract
We investigate the dark matter distribution in the spiral galaxy ESO0140040, employing the most widely used density profiles: the pseudo-isothermal, exponential sphere, Burkert, Navarro-Frenk-White, Moore and Einasto profiles. We infer the model parameters and estimate the total dark matter [...] Read more.
We investigate the dark matter distribution in the spiral galaxy ESO0140040, employing the most widely used density profiles: the pseudo-isothermal, exponential sphere, Burkert, Navarro-Frenk-White, Moore and Einasto profiles. We infer the model parameters and estimate the total dark matter content from the rotation curve data. For simplicity, we assume that dark matter distribution is spherically symmetric without accounting for the complex structure of the galaxy. Our predictions are compared with previous results and the fitted parameters are statistically confronted for each profile. We thus show that although one does not include the galaxy structure it is possible to account for the same dynamics assuming that dark matter provides a non-zero pressure in the Newtonian approximation. In this respect, we solve the hydrostatic equilibrium equation and construct the dark matter pressure as a function for each profile. Consequently, we discuss the dark matter equation of state and calculate the speed of sound in dark matter. Furthermore, we interpret our results in view of our approach and we discuss the role of the refractive index as an observational signature to discriminate between our approach and the standard one. Full article
(This article belongs to the Special Issue Dark Cosmology: Shedding Light on Our Current Universe)
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10 pages, 239 KiB  
Brief Report
Equiaffine Braneworld
by Fan Zhang
Galaxies 2020, 8(4), 73; https://doi.org/10.3390/galaxies8040073 - 21 Oct 2020
Cited by 1 | Viewed by 1811
Abstract
Higher dimensional theories, wherein our four dimensional universe is immersed into a bulk ambient, have received much attention recently, and the directions of investigation had, as far as we can discern, all followed the ordinary Euclidean hypersurface theory’s isometric immersion recipe, with the [...] Read more.
Higher dimensional theories, wherein our four dimensional universe is immersed into a bulk ambient, have received much attention recently, and the directions of investigation had, as far as we can discern, all followed the ordinary Euclidean hypersurface theory’s isometric immersion recipe, with the spacetime metric being induced by an ambient parent. We note, in this paper, that the indefinite signature of the Lorentzian metric perhaps hints at the lesser known equiaffine hypersurface theory as being a possibly more natural, i.e., less customized beyond minimal mathematical formalism, description of our universe’s extrinsic geometry. In this alternative, the ambient is deprived of a metric, and the spacetime metric becomes conformal to the second fundamental form of the ordinary theory, therefore is automatically indefinite for hyperbolic shapes. Herein, we advocate investigations in this direction by identifying some potential physical benefits to enlisting the help of equiaffine differential geometry. In particular, we show that a geometric origin for dark energy can be proposed within this framework. Full article
(This article belongs to the Special Issue Dark Cosmology: Shedding Light on Our Current Universe)
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