scholarly journals Intrinsic Nature of Dark Matter in the Galactic Halo

2020 ◽  
Author(s):  
UGUR CAMCI
Keyword(s):  
Dark Matter ◽  
Equation Of State ◽  
Modified Gravity ◽  
Galactic Halo ◽  
Galactic Halos ◽  
General Function ◽  
Intrinsic Nature ◽  
Flat Rotation Curves ◽  
Geometric Equation ◽  
Gravity Theories

We obtain more straightforwardly the main intrinsic features of dark matter distribution in the halos of galaxies by considering the spherically symmetric space-time, which satisfies the flat rotational curve condition, and the geometric equation of state resulting from the modified gravity theory. In order to measure the equation of state for dark matter in the galactic halo, we provide a general formalism taking into account the modified f(X) gravity theories. Here, f(X) is a general function of X∈{R,G,T}, where R,G and T are the Ricci scalar, the Gauss-Bonnet scalar and the torsion scalar, respectively. These theories yield that the flat rotation curves appear as a consequence of the additional geometric structure accommodated by those of modified gravity theories. Constructing a geometric equation of state wX≡pX/ρX and inspiring by some values of the equation of state for the ordinary matter, we infer the properties of dark matter in galactic halos of galaxies.

Galaxy clustering and the dark-matter problem

1986 ◽  
Vol 320 (1556) ◽  
pp. 517-541 ◽  
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Density Fluctuations ◽  
Small Scale ◽  
Galactic Halos ◽  
Galaxy Clustering ◽  
Simple Assumption ◽  
Scale Free ◽  
The Galaxy ◽  
Flat Rotation Curves

Recent observational and theoretical results on galaxy clustering are reviewed. A major difficulty in relating observations to theory is that the former refer to luminous material whereas the latter is most directly concerned with the gravitationally dominant but invisible dark matter. The simple assumption that the distribution of galaxies generally follows that of the mass appears to conflict with evidence suggesting that galaxies of different kinds are clustered in different ways. If galaxies are indeed biased tracers of the mass, then dynamical estimates of the mean cosmic density, which give Ω « 0.2 may underestimate the global value of Ω. There are now several specific models for the behaviour of density fluctuations from very early times to the present epoch. The late phases of this evolution need to be followed by N -body techniques; simulations of scale-free universes and of universes dominated by various types of elementary particles are discussed. In the former case, the models evolve in a self-similar way; the resulting correlations have a steeper slope than that oberved for the galaxy distribution unless the primordial power spectral index n « 2. Universes dominated by light neutrinos acquire a large coherence length at early times. As a result, an early filamentary phase develops into a present day distribution that is more strongly clustered than observed galaxies and is dominated by a few clumps with masses larger than those of any known object. If the dark matter consists of ‘cold’ particles such as photinos or axions, then structure builds up from subgalactic scales in a roughly hierarchical way. The observed pattern of galaxy clustering can be reproduced if either Ω « 0.2 and the galaxies are distributed as the mass, or if Ω — 1, H 0 = 50 km s -1 Mpc -1 and the galaxies form only at high peaks of the smoothed linear density field. The open model, however, is marginally ruled out by the observed small-scale isotropy of the microwave background, whereas the flat one is consistent with such observations. With no further free parameters a flat cold dark-matter universe produces the correct abundance of rich galaxy clusters and of galactic halos; the latter have flat rotation curves with amplitudes spanning the observed range. Preliminary calculations indicate that the properties of voids may be consistent with the data, but the correlations of rich clusters appear to be somewhat weaker than those reported for Abell clusters.

Interacting cosmological viscous fluid with Little Rip and Pseudo Rip solutions in f(R) gravity

2018 ◽  
Vol 15 (02) ◽  
pp. 1850028 ◽  
Author(s):  
R. D. Boko ◽  
M. J. S. Houndjo ◽  
J. Tossa
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Viscous Fluid ◽  
Modified Gravity ◽  
Infinite Time ◽  
Two Fluids ◽  
Viscosity Models ◽  
Time Singularities ◽  
Analytic Expressions

In this paper, we investigate the evolution of the equation of state of the interacting viscous dark energy in [Formula: see text] gravity. We first consider the case when the dark energy does not interact with the dark matter and after, the case where there is a coupling between these dark components. The viscosity and the interaction between the two fluids are parameterized by constants [Formula: see text] and [Formula: see text] respectively for which a detailed investigation on the cosmological implications has been done. In the later part of the paper, we explore some bulk viscosity models with Little and Pseudo Rip infinite time singularities within [Formula: see text] modified gravity. We obtain analytic expressions for characteristic properties of these cosmological models.

A study on the modified holographic Ricci dark energy in logarithmic f(T) gravity

2013 ◽  
Vol 91 (4) ◽  
pp. 351-354 ◽  
Author(s):  
Antonio Pasqua ◽  
Surajit Chattopadhyay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Modified Gravity ◽  
State Parameter ◽  
Ricci Dark Energy ◽  
Equation Of State Parameter ◽  
Interaction Term ◽  
The Universe

In this paper, we have studied and investigated the behavior of a modified holographic Ricci dark energy (DE) model interacting with pressureless dark matter (DM) under the theory of modified gravity, dubbed logarithmic f(T) gravity. We have chosen the interaction term between DE and DM in the form Q = 3γHρm and investigated the behavior of the torsion, T, the Hubble parameter, H, the equation of state parameter, ωDE, the energy density of DE, ρDE, and the energy density contribution due to torsion, ρT, as functions of the redshift, z. We have found that T increases with the redshift, z, H increases with the evolution of the universe, ωDE has a quintessence-like behavior, and both energy densities increase going from higher to lower redshifts.

scholarly journals The radial acceleration relation and its emergent nature

2019 ◽  
Vol 15 (S359) ◽  
pp. 457-459
Author(s):  
Davi C. Rodrigues ◽  
Valerio Marra
Keyword(s):  
Dark Matter ◽  
Modified Gravity ◽  
Recent Analysis ◽  
Radial Acceleration ◽  
Modified Gravity Theories ◽  
Bayesian Test ◽  
Gravity Theories

AbstractWe review some of our recent results about the Radial Acceleration Relation (RAR) and its interpretation as either a fundamental or an emergent law. The former interpretation is in agreement with a class of modified gravity theories that dismiss the need for dark matter in galaxies (MOND in particular). Our most recent analysis, which includes refinements on the priors and the Bayesian test for compatibility between the posteriors, confirms that the hypothesis of a fundamental RAR is rejected at more than 5σ from the very same data that was used to infer the RAR.

Dark matter halo with charge in pseudo-spheroidal geometry

2021 ◽  
pp. 2150178
Author(s):  
Mithun Ghosh
Keyword(s):  
Dark Matter ◽  
Equation Of State ◽  
Perfect Fluid ◽  
Circular Orbit ◽  
Galactic Halo ◽  
Rotational Velocity ◽  
Dark Matter Halo ◽  
Cosmological Observations ◽  
The Stability ◽  
Spheroidal Geometry

The concept of dark matter (DM) hypothesis comes out as a result from the input of the observed flat rotational velocity. With the assumption that the galactic halo is pseudo-spheroidal and filled with charged perfect fluid, we have obtained a solution which has inkling to a (nearly) flat universe, compatible with the modern day cosmological observations. Various other important aspects of the solution such as attractive gravity in the halo region and the stability of the circular orbit are also explored. Also, the matter in the halo region satisfies the known equation of state which indicates its non-exotic nature.

scholarly journals Origin and evolution of structure and nucleosynthesis for galaxies in the local group

2014 ◽  
Vol 29 (14) ◽  
pp. 1430012 ◽  
Author(s):  
G. J. Mathews ◽  
A. Snedden ◽  
L. A. Phillips ◽  
I.-S. Suh ◽  
J. Coughlin ◽  
...  
Keyword(s):  
Dark Matter ◽  
Local Group ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Dwarf Galaxies ◽  
Gravitational Interaction ◽  
Galactic Halos ◽  
Origin And Evolution ◽  
Spiral Density Waves ◽  
Streaming Flows

The Milky Way is the product of a complex evolution of generations of mergers, collapse, star formation, supernova and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark matter halos, spiral density waves, and emerging dark energy. In this review we summarize observational evidence and discuss recent calculations concerning the formation, evolution nucleosynthesis in the galaxies of the Local Group (LG). In particular, we will briefly summarize observations and simulations for the dwarf galaxies and the two large spirals of the LG. We discuss how galactic halos form within the dark matter filaments that define a super-galactic plane. Gravitational interaction along this structure leads to streaming flows toward the two dominant galaxies in the cluster. These simulations and observations also suggest that a significant fraction of the Galactic halo formed as at large distances and then arrived later along these streaming flows. We also consider the insight provided by observations and simulations of nucleosynthesis both within the galactic halo and dwarf galaxies in the LG.

scholarly journals Can quantum theory explain dark matter?

2004 ◽  
Vol 220 ◽  
pp. 497-498
Author(s):  
A. D. Ernest
Keyword(s):  
Dark Matter ◽  
Quantum Theory ◽  
Gravitational Collapse ◽  
Galactic Halo ◽  
Galactic Evolution ◽  
Rotation Curves ◽  
Visible Matter ◽  
Flat Rotation Curves ◽  
Classical Analogue ◽  
Inherent Stability

Certain solutions to a gravitational form of Schrödinger's equation can yield stable, macroscopic eigenstate solutions having no classical analogue, with properties resembling those of dark matter. Some more tractable solutions show: (1) radiative lifetimes far exceeding the universe's age, implying negligible emission and inherent stability w.r.t. gravitational collapse, (2) negligible interaction with EMR and visible matter, (3) potential to give rise to flat rotation curves and (4) eigenstate energies and “sizes” consistent with that expected for the galactic halo. Traditional baryonic particles occupying such eigenstates will be invisible and weakly interacting, and may be assimilated into galactic evolution scenarios without significantly disturbing BBN ratios. It is proposed that such structures may explain the nature and origin of dark matter.

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