Dark Matter Equation Research Articles

Exploring non-radial oscillation modes in dark matter admixed neutron stars

Because of their extreme densities and consequently, gravitational potential, compact objects such as neutron stars can prove to be excellent captors of dark matter particles. Considering purely gravitational interactions between dark and hadronic matter, we construct dark matter admixed stars composed of two-fluid matter subject to current astrophysical constraints on maximum mass and tidal deformability. We choose a wide range of parameters to construct the dark matter equation of state, and the DDME2 parameterization for the hadronic equation of state. We then examine the effect of dark matter on the stellar structure, tidal deformability and non-radial modes considering the relativistic Cowling approximation. We find the effect on p-modes is substantial, with frequencies decreasing up to the typical f-mode frequency range for most stars with a dark matter halo. The effects on the f-mode frequency are less extreme. Finally, we find the most probable values of the dark matter parameters that satisfy the observational constraints.

Analogy of space-time as an elastic medium - Estimation of a creep coefficient of space from space data via the MOND theory and the gravitational lensing effect - the ball cluster and via time data from the GPS effect- comparison, discussion and implication of the results for dark matter and Einstein's field equation

Analogy of space-time as an elastic medium - Estimation of a creep coefficient of space from space data via the MOND theory and the gravitational lensing effect - the ball cluster and via time data from the GPS effect- comparison, discussion and implication of the results for dark matter and Einstein's field equation

Effects of dark matter on the spontaneous scalarization in neutron stars

Dark matter, an important portion of compact objects, can influence different phenomena in neutron stars. The spontaneous scalarization in the scalar-tensor gravity has been proposed for neutron stars. Here, we investigate the spontaneous scalarization in dark matter admixed neutron stars. Applying the dark matter equations of state, we calculate the structure of scalarized neutron stars containing dark matter. The dark matter equations of state are based on observational data from the rotational curves of galaxies and the fermionic self-interacting dark matter. Our results verify that the spontaneous scalarization is affected by the dark matter pressure in neutron stars. Depending on the central density of scalarized dark matter admixed neutron stars, the dark matter pressure alters the central scalar field. The increase of dark matter pressure in low-density scalarized stars amplifies the central scalar field. However, the pressure of dark matter in high-density scalarized stars suppresses the central scalar field. Our calculations confirm that the stars in the merger event GW170817 and in the low-mass X-ray binary 4U 1820-30 can be scalarized dark matter admixed neutron stars.

Impact of cold dark matter and variable equations of state on the stability of thin-shell wormholes

The goal of this research is to better understand how two identical black hole copies, bounded by a cold dark matter halo, produce and stabilize thin-shell wormholes. The occurrence of a cold dark matter halo is discovered to increase the black hole’s horizon radius. Investigating the stable geometry of these wormholes by linearized radial perturbation analysis is the main objective of the work. It is noteworthy that the development of thin-shell wormholes with reduced energy limitations is associated with the presence of a cold dark matter halo. We study how the stability of the wormholes is affected by variable equations of state, including phantom-like, variable Chaplygin, and barotropic equations of state. The question emphasizes how crucial the existence of a cold dark matter halo is to preserving stable thin-shell wormhole configurations. The findings shed light on the interactions between a cold dark matter halo and wormholes, which improved our knowledge of both phenomena and their possible consequences for extraterrestrial travel.

Preliminary Study of Dark-matter-dominated Systems: Further Analysis for Galactic Dark Matter Halos with Pressure

Low-surface-brightness galaxies are excellent laboratories, where stars and baryonic matter act as tracers of the gravitational potential of the dark matter halo. If dark matter is modeled as a perfect fluid, then spherically symmetric and static dark matter halos in hydrostatic equilibrium demand that dark matter should have an intrinsic pressure that counteracts the gravitational attraction that the dark matter halo exerts on itself. This static fluid (a dark-matter-dominated system, where the presence of baryons is negligible) has a specific equation of state for each rotational velocity profile of the stars in galaxies. In this work, we study the dark matter equation of state needed for the self-gravitating object to produce a gravitational potential such that the tracers follow the universal rotational velocity profile for stars of spiral galaxies proposed by Persic et al. and analyze the properties of the self-gravitating structures that emerge from this equation of state. The resulting configurations explaining the observed rotational speeds are found to be unstable. We conclude that the halo is not in hydrostatic equilibrium, it is nonspherically symmetric, or it is not static if the universal velocity profile should be valid for fitting the rotational velocity curve of the galaxies.

Restoring cosmological concordance with axion-like early dark energy and dark matter characterized by a constant equation of state?

The Hubble tension persists as a challenge in cosmology. Even early dark energy (EDE) models, initially considered the most promising for alleviating the Hubble tension, fall short of addressing the issue without exacerbating other tensions, such as the S 8 tension. Considering that a negative dark matter (DM) equation of state (EoS) parameter is conducive to reduce the value of the σ 8 parameter, we extend the axion-like EDE model in this paper by replacing the cold dark matter (CDM) with DM characterized by a constant EoS w dm (referred to as WDM hereafter). We then impose constraints on this axion-like EDE extension model, along with three other models: the axion-like EDE model, ΛWDM, and ΛCDM. These constraints are derived from a comprehensive analysis incorporating data from the Planck 2018 cosmic microwave background, baryon acoustic oscillations, and the Pantheon compilation, as well as a prior on H 0 (i.e. H 0 = 73.04 ± 1.04, based on the latest local measurement by Riess et al) and a Gaussianized prior on S 8 (i.e. S 8 = 0.766 ± 0.017, determined through the joint analysis of KID1000+BOSS+2dLenS). We find that although the new model maintains the ability to alleviate the Hubble tension to ∼1.4σ, it still exacerbates the S 8 tension to a level similar to that of the axion-like EDE model.

Influence of dark matter equation of state on the axial gravitational ringing of supermassive black holes

Influence of dark matter equation of state on the axial gravitational ringing of supermassive black holes

IWDM: the fate of an interacting non-cold dark matter — vacuum scenario

In most cosmological models, the equation of state of the dark matter is assumed to be zero, which means that the dark matter is pressure-less or cold. While this hypothesis is based on the abundance of cold dark matter in the universe, however, there is no compelling reason to assume that the equation of state of dark matter is exactly zero. A more general approach would be to allow for a range of values for the dark matter equation of state and use the observational data to determine which values are most likely. With the increasing accuracy of experimental data, we have chosen to explore the possibility of interacting non-cold dark matter - vacuum scenario, where the equation of state of the dark matter is constant but can take different values within a specific range. Using the Cosmic Microwave Background (CMB) anisotropies and the CMB lensing reconstruction from the Planck legacy release, plus other non-CMB measurements, namely, the baryon acoustic oscillations distance measurements, and the Pantheon catalogue from Type Ia Supernovae, we have analyzed this scenario and found that a non-zero value for the dark matter equation of state is preferred with a confidence level of over 68%. While this is not significant by itself, however, it does suggest that investigating the possibility of non-cold dark matter in the universe is worth exploring further to gain a better understanding of the nature of dark matter.

Emergence of the Gambier equation in cosmology

In this paper, we show how the Gambier equation arises in connection to Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology and a Dark Matter equation of state. Moreover, we provide a correspondence between the Friedmann equations and the Gambier equations that possess the Painlevé property in (2 + 1) dimensions. We also consider special cases of the Gambier G27 equation such as the generalized Pinney equation. For an extended FLRW model with dynamic scalar field as matter model, the Einstein equations correspond to the Milne–Pinney equation which in turn can be mapped to the parametric Gambier equation of second order.

Extended Bose–Einstein condensate dark matter in viscous Gauss–Bonnet gravity

In this paper, we study the [Formula: see text] gravity model with an interacting model by flat-FRW metric in a viscous fluid. We consider that the universe dominates with components of dark matter and dark energy. This means that the dark matter component derives from Extended Bose–Einstein Condensate (EBEC) and the components of dark energy arise from the [Formula: see text] gravity. After obtaining the Einstein equation, the energy density and the pressure of dark energy are written in terms of the geometry of the curvature and the Gauss–Bonnet terms, and components of dark matter and viscous fluid. Also, the corresponding continuity equations are written with the presence of interaction terms. In what follows, we employ the EBEC regime instead of the normal dark matter by the dark matter Equation of State (EoS) as [Formula: see text], which arises from the gravitational form. The EoS can be expressed from the perspective of the virial expansion, in which the first and second terms represent normal dark matter and quantum ground state. Next, the corresponding Friedmann equations reconstruct in terms of the redshift parameter, then by using the scenario of the power-law cosmology for the scale factor, we fit the present model with the Hubble amounts of 51 supernova data by the likelihood analysis. In that case, we acquire the cosmological parameters of dark energy in terms of the redshift parameter, and by plotting these graphs, we see that the universe is currently undergoing an accelerated expansion phase. Finally, we investigate the stability of the present model with the sound speed parameter.

Dark matter admixed neutron star properties in light of gravitational wave observations: A two fluid approach

We consider the effect of density dependent dark matter on the neutron star mass, radius, and tidal deformability. Nuclear matter (normal matter) as well as the fermionic dark matter sector is considered in a mean field model. We adopt the two fluid formalism to investigate the effect of dark matter on the neutron star properties. In the two fluid picture, there is no direct interaction between the dark matter and the nuclear matter. Rather these two sectors interact only through gravitational interaction. The nuclear matter sector is described by the $\ensuremath{\sigma}\ensuremath{-}\ensuremath{\omega}\ensuremath{-}\ensuremath{\rho}$ meson interaction in the ``FSU2R'' parametrization. In the dark matter sector, we use the Bayesian parameter optimization technique to fix the unknown parameters in the dark matter equation of state. In the two fluid picture, we solve the coupled Tolman-Oppenheimer-Volkoff (TOV) equations to obtain the mass and radius of dark matter admixed neutron stars (DANSs). We also estimate the effect of the density dependent dark matter sector on the tidal deformability of dark matter admixed neutron stars (DANSs).

A novel approach to autoparallels for the theories of symmetric teleparallel gravity

Although the autoparallel curves and the geodesics coincide in the Riemannian geometry in which only the curvature is nonzero among the nonmetricity, the torsion and the curvature, they define different curves in the non-Riemannian ones. We give a novel approach to autoparallel curves and geodesics for theories of the symmetric teleparallel gravity written in the coincident gauge. Then we apply our autoparallel equation to a Schwarzschild-type metric and give remarks about dark matter and orbit equation.

Impacts of dark matter on the f -mode oscillation of hyperon star

We investigate the $f$-mode oscillation of the dark matter admixed hyperon star within the relativistic Cowling approximation. The macroscopic properties are calculated with the relativistic mean-field equation of states by assuming that the dark matter particles are inside the star. The $f$-mode oscillation frequencies (only for $l=2$) are calculated with four different neutron star equation of states. We also check the effects of hyperons/dark matter and hyperons with dark matter equation of states on the $f$-mode oscillations varying with different astrophysical quantities such as mass ($M$), radius ($R$), compactness ($M/R$), surface red-shift ($Z_s$), average density ($\bar{\rho}$), dimensionless tidal deformability ($\Lambda$) of the neutron star. Significant changes have been seen in the $f$-mode frequencies with and without hyperons/dark matter or hyperons+dark matter. Substantial correlations are observed between canonical frequencies and $\Lambda$ ($f_{1.4}-\Lambda_{1.4}$) and maximum frequencies and canonical $\Lambda$ ( $f_{max}-\Lambda_{1.4}$).

Stellar model of compact star with dark matter equation of state

Stellar model of compact star with dark matter equation of state

Viscous interaction and stability on dark matter Bose–Einstein condensation with modified Chaplygin gas

In this paper, viscous cosmological dynamics are studied in the presence of dark matter Bose–Einstein condensation by curved-FRW background. For this purpose, we use the BEC regime rather than normal dark matter (cold dark matter or barotropic dark matter) with the dark matter equation of state as [Formula: see text], which arises from the gravitational form. Therefore, we obtain the corresponding continuity equations with the existence of the universe components by considering an interacting model with modified Chaplygin gas. Afterward, we derive the energy density and the pressure of dark energy in terms of the redshift parameter. And then, by introducing a parametrization function and fitting it with 51 supernova data with the likelihood analysis, we find the cosmological parameters versus redshift parameter. In what follows, we plot the corresponding dynamic graphs proportional to redshift, and then we represent that the universe is currently undergoing an accelerated expansion phase. Finally, we explore the stability and the instability of the present model with the sound speed parameter.

Is non-particle dark matter equation of state parameter evolving with time?

Recently, the so-called Hubble Tension, i.e. the mismatch between the local and the cosmological measurements of the Hubble parameter, has been resolved when non-particle dark matter is considered which has a negative equation of state parameter (omega approx -,0.01). We investigate if such a candidate can successfully describe the galactic flat rotation curves. It is found that the flat rotation curve feature puts a stringent constraint on the dark matter equation of state parameter omega and omega approx -,0.01 is not consistent with flat rotational curves, observed around the galaxies. However, a dynamic omega of non-particle dark matter may overcome the Hubble tension without affecting the flat rotation curve feature.

Constraints on interacting dark energy models through cosmic chronometers and Gaussian process

In this paper, after reconstructing the redshift evolution of the Hubble function by adopting Gaussian process techniques, we estimate the best-fit parameters for some flat Friedmann cosmological models based on a modified Chaplygin gas interacting with dark matter. In fact, the expansion history of the Universe will be investigated because passively evolving galaxies constitute cosmic chronometers. An estimate for the present-day values of the deceleration parameter, adiabatic speed of sound within the dark energy fluid, effective dark energy, and dark matter equation of state parameters is provided. By this, we mean that the interaction term between the two dark fluids, which breaks the Bianchi symmetries, will be interpreted as an effective contribution to the dark matter pressure similarly to the framework of the “Generalized Dark Matter”. We investigate whether the estimates of the Hubble constant and of the present-day abundance of dark matter are sensitive to the dark matter–dark energy coupling. We will also show that the cosmic chronometers data favor a cold dark matter, and that our findings are in agreement with the Le Châtelier–Braun principle according to which dark energy should decay into dark matter.

Imprint of Pressure on Characteristic Dark Matter Profiles: The Case of ESO0140040

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.

Spherical collapse in generalized dark matter models

The influence of considering a generalized dark matter (GDM) model, which allows for a non-pressure-less dark matter and a non-vanishing sound speed in the non-linear spherical collapse model is discussed for the Einstein-de Sitter-like (EdSGDM) and $\Lambda$GDM models. By assuming that the vacuum component responsible for the accelerated expansion of the Universe is not clustering and therefore behaving similarly to the cosmological constant $\Lambda$, we show how the change in the GDM characteristic parameters affects the linear density threshold for collapse of the non-relativistic component ($\delta_{\rm c}$) and its virial overdensity ($\Delta_{\rm V}$). We found that the generalized dark matter equation of state parameter $w_{\rm gdm}$ is responsible for lower values of the linear overdensity parameter as compared to the standard spherical collapse model and that this effect is much stronger than the one induced by a change in the generalized dark matter sound speed $c^2_{\rm s, gdm}$. We also found that the virial overdensity is only slightly affected and mostly sensitive to the generalized dark matter equation of state parameter $w_{\rm gdm}$. These effects could be relatively enhanced for lower values of the matter density. Finally, we found that the effects of the additional physics on $\delta_{\rm c}$ and $\Delta_{\rm V}$, when translated to non-linear observables such as the halo mass function, induce an overall deviation of about 40\% with respect to the standard $\Lambda$CDM model at late times for high mass objects. However, within the current linear constraints for $c^2_{\rm s, gdm}$ and $w_{\rm gdm}$, we found that these changes are the consequence of properly taking into account the correct linear matter power spectrum for the GDM model while the effects coming from modifications in the spherical collapse model remain negligible.

Possibility of traversable wormhole formation in the dark matter halo with istropic pressure

We explore the possibility of traversable wormhole formation in the dark matter halos. We obtain the exact solutions of the spherical symmetry traversable wormhole with isotropic pressure condition, based on the Navarro–Frenk–White (NFW), Thomas–Fermi (TF) and Pseudo Isothermal (PI) matter density profiles. The derived traversable wormhole solution satisfies the flare-out condition for a specific dark matter center density and equation of state. We extend the spherical symmetry traversable wormhole solutions to an axisymmetric one. The weak energy condition (WEC) and null energy condition (NEC) are then checked near the wormhole throat, and we find that these traversable wormholes violate the WEC and NEC. Our traversable wormhole solutions show that the dark matter at the center of wormhole spacetime will be redistributed by the presence of a traversable wormhole, and the behavior of dark matter density is similar to a black hole spike.