Two Analytic Relations Connecting the Hot Gas Astrophysics with the Cold Dark Matter Model for Galaxy Clusters

Galaxy clusters are good targets for examining our understanding of cosmology. Apart from numerical simulations and gravitational lensing, X-ray observation is the most common and conventional way to analyze the gravitational structures of galaxy clusters. Therefore, it is valuable to have simple analytical relations that can connect the observed distribution of the hot, X-ray-emitting gas to the structure of the dark matter in the clusters as derived from simulations. In this article, we apply a simple framework that can analytically connect the hot gas empirical parameters with the standard parameters in the cosmological cold dark matter model. We have theoretically derived two important analytic relations, r s ≈ 3 r c and ρ s ≈ 9 β kT / 8 π Gm g r c 2 , which can easily relate the dark matter properties in galaxy clusters with the hot gas properties. This can give a consistent picture describing gravitational astrophysics for galaxy clusters by the hot gas and cold dark matter models.

Single parameter model for cosmic scale photon redshift in a closed Universe

A successful single parameter model has been formulated to match the observations of photons from type 1a supernovae which were previously used to corroborate the standard 𝛬 cold dark matter model. The new single parameter model extrapolates all the way back to the cosmic background radiation (CMB) without requiring a separate model to describe inflation of the space dimensions after the Big Bang. The model for the redshift progression of a photon is: 1 + z =\(\frac{\text{sin}\left(\frac{13.8}{T}\right)\pi /2}{\text{sin}\left(\frac{t}{T}\right)\pi /2}\) T is the fitted parameter and t is the time when the photon was emitted, both measured in billions of years from time zero in the Big Bang. The angle is expressed in radians. The number 13.8 should be updated if an improved estimate for the time elapsed since the Big Bang is found. The single parameter model assumes that spacetime forms a finite symmetrical manifold with positive curvature.

Resolving XENON excess with decaying cold dark matter

We propose a decaying cold dark matter model to explain the excess of electron recoil observed at the XENON1T experiment. In this scenario, the daughter dark matter from the parent dark matter decay easily obtains velocity large enough to saturate the peak of the electron recoil energy around 2.5 keV, and the observed signal rate can be fulfilled by the parent dark matter with a mass of order 10–200 MeV and a lifetime larger than the age of Universe. We verify that this model is consistent with experimental limits from dark matter detections, Cosmic microwave background and large scale structure experiments.

Single parameter model for cosmic scale photon redshift in a closed Universe

A successful single parameter model has been formulated to match the observations of photons from type 1a supernovae which were previously used to corroborate the standard 𝛬 cold dark matter model. The new single parameter model extrapolates all the way back to the cosmic background radiation (CMB) without requiring a separate model to describe inflation of the space dimensions after the Big Bang. The model for the redshift progression of a photon is: 1 + z =\(\frac{\text{sin}\left(\frac{13.8}{T}\right)\pi /2}{\text{sin}\left(\frac{t}{T}\right)\pi /2}\) T is the fitted parameter and t is the time when the photon was emitted, both measured in billions of years from time zero in the Big Bang. The angle is expressed in radians. The number 13.8 should be updated if an improved estimate for the time elapsed since the Big Bang is found. The single parameter model assumes that spacetime forms a finite symmetrical manifold with positive curvature.

A high-resolution cosmological simulation of a strong gravitational lens

We present a cosmological hydrodynamical simulation of a 1013 M⊙ galaxy group and its environment (out to 10 times the virial radius) carried out using the Eagle model of galaxy formation. Exploiting a novel technique to increase the resolution of the dark matter calculation independently of that of the gas, the simulation resolves dark matter haloes and subhaloes of mass 5 × 106 M⊙. It is therefore useful for studying the abundance and properties of the haloes and subhaloes targeted in strong lensing tests of the cold dark matter model. We estimate the halo and subhalo mass functions and discuss how they are affected both by the inclusion of baryons in the simulation and by the environment. We find that the halo and subhalo mass functions have lower amplitude in the hydrodynamical simulation than in its dark matter only counterpart. This reflects the reduced growth of haloes in the hydrodynamical simulation due to the early loss of gas by reionisation and galactic winds and, additionally, in the case of subhaloes, disruption by enhanced tidal effects within the host halo due to the presence of a massive central galaxy. The distribution of haloes is highly anisotropic reflecting the filamentary character of mass accretion onto the cluster. As a result, there is significant variation in the number of structures with viewing direction. The median number of structures near the centre of the halo, when viewed in projection, is reduced by a factor of two when baryons are included.

Creating a galaxy lacking dark matter in a dark matter-dominated universe

ABSTRACT We use hydrodynamical cosmological simulations to show that it is possible to create, via tidal interactions, galaxies lacking dark matter (DM) in a DM-dominated universe. We select dwarf galaxies from the NIHAO project, obtained in the standard cold dark matter model and use them as initial conditions for simulations of satellite–central interactions. After just one pericentric passage on an orbit with a strong radial component, NIHAO dwarf galaxies can lose up to 80 per cent of their DM content, but, most interestingly, their central (≈8 kpc) DM-to-stellar mass ratio changes from a value of ∼25, as expected from numerical simulations and abundance matching techniques, to roughly unity as reported for NGC 1052-DF2 and NGC 1054-DF4. The stellar velocity dispersion drops from ∼30 $\, \rm km\, s^{-1}$ before infall to values as low as 6 ± 2 $\, \rm km\, s^{-1}$. These, and the half-light radius around 3 kpc, are in good agreement with observations from van Dokkum and collaborators. Our study shows that it is possible to create a galaxy without DM starting from typical dwarf galaxies formed in a DM-dominated universe, provided they live in a dense environment.

Optimizing tomography for weak gravitational lensing surveys

ABSTRACT The subject of this paper is optimization of weak lensing tomography: we carry out numerical minimization of a measure of total statistical error as a function of the redshifts of the tomographic bin edges by means of a Nelder–Mead algorithm in order to optimize the sensitivity of weak lensing with respect to different optimization targets. Working under the assumption of a Gaussian likelihood for the parameters of a w0wa CDM (cold dark matter) model and using euclid’s conservative survey specifications, we compare an equipopulated, equidistant, and optimized bin setting and find that in general the equipopulated setting is very close to the optimal one, while an equidistant setting is far from optimal and also suffers from the ad hoc choice of a maximum redshift. More importantly, we find that nearly saturated information content can be gained using already few tomographic bins. This is crucial for photometric redshift surveys with large redshift errors. We consider a large range of targets for the optimization process that can be computed from the parameter covariance (or equivalently, from the Fisher matrix), extend these studies to information entropy measures such as the Kullback–Leibler divergence and conclude that in many cases equipopulated binning yields results close to the optimum, which we support by analytical arguments.

The observed discordances in cosmology signaling new Physics

The measured values for the cosmic expansion rate, the cosmic radius, the cosmic age, etc. vary with a direct or an indirect methodology. These discrepancies known as the cosmological crisis imply the existence of a new physical field. The coupling of matter to the field causes the ratio between a being measured mass of matter and a reference mass to vary with the field. Any experiment can only measure the relative ratio rather than the absolute mass of matter. Apparently, there are two representations in describing the field dependence of the ratio: the reference (being measured) mass varies with the field while the being measured (reference) mass does not. Therefore, the measured value of every quantity depends on the choice of the representations. A representation is selected based on the conscious or unconscious assumptions in an experiment. This new field can resolve the discrepancies as well as drive the late-time cosmic acceleration. The new closed cosmic model here can remove the tensions in the standard cold dark matter model with Λ being the cosmological constant.

The observed discordances in cosmology signaling new Physics

The measured values for the cosmic expansion rate, the cosmic radius, the cosmic age, etc. vary with a direct or an indirect methodology. These discrepancies known as the cosmological crisis imply the existence of a new physical field. The coupling of matter to the field causes the ratio between a being measured mass of matter and a reference mass to vary with the field. Any experiment can only measure the relative ratio rather than the absolute mass of matter. Apparently, there are two representations in describing the field dependence of the ratio: the reference (being measured) mass varies with the field while the being measured (reference) mass does not. Therefore, the measured value of every quantity depends on the choice of the representations. A representation is selected based on the conscious or unconscious assumptions in an experiment. This new field can resolve the discrepancies as well as drive the late-time cosmic acceleration. The new closed cosmic model here can remove the tensions in the standard cold dark matter model with Λ being the cosmological constant.

Extended General Relativity for a Curved Universe

The Planck Legacy recent release revealed the presence of an enhanced lensing amplitude in the cosmic microwave background, which confirms the early universe positive curvature with a confidence level exceeding 99%. Besides, the observed gravitational lensing within several galaxy clusters is higher than that estimated through the standard lambda cold dark matter model by an order of magnitude. While general relativity works perfectly well in the present universe where the spacetime is almost flat, it should be enhanced to account for the pre-existing universal curvature. This study presents new enhanced field equations utilising Einstein–Hilbert action. The enhanced field equations are reduced to Einstein field equations in a flat universe.