Search Results (53)

The standard models of particle physics and of cosmology have been enormously successful in correlating a large amount of data. However, there are missing pieces and we are still far from what the ultimate model may look like. We give a broad perspective of both the achievements and of the missing pieces and discuss what may lie beyond. Full article

The richest and largest structures in the cosmic web are galaxy superclusters, their complexes (associations of several almost connected very rich superclusters), and planes. Superclusters represent a special environment where the evolution of galaxies and galaxy groups and clusters differs from the evolution of these systems in a low-density environment. The richest galaxy clusters reside in superclusters. The richest superclusters in the nearby Universe form a quasiregular pattern with the characteristic distance between superclusters 120–140 h⁻¹ Mpc. Moreover, superclusters in the nearby Universe lie in two huge perpendicular planes with the extent of several hundreds of megaparsecs, the Local Supercluster plane and the Dominant supercluster plane. The origin of these patterns in the supercluster distribution is not yet clear, and it is an open question whether the presence of such structures can be explained within the ΛCDM cosmological model. This review presents a brief story of superclusters, their discovery, definitions, main properties, and large-scale distribution. Full article

Evidence is presented for dark energy resulting directly from star formation. A survey of stellar mass density measurements, SMD(a), as a function of universe scale size a, was found to be described by a simple CPL w₀ − w_a parameterisation that was in good agreement with the dark energy results of Planck 2018, Pantheon+ 2022, the Dark Energy Survey 2024, and the Dark Energy Spectroscopic Instrument 2024. The best-fit CPL values found were w₀ = −0.90 and w_a = −1.49 for SMD(a), and w₀ = −0.94 and w_a = −0.76 for SMD(a)^0.5, corresponding with, respectively, good and very good agreement with all dark energy results. The preference for SMD(a)^0.5 suggests that it is the temperature of astrophysical objects that determines the dark energy density. The equivalent energy of the information/entropy of gas and plasma heated by star and structure formations is proportional to temperature, and is then a possible candidate for such a dark energy source. Information dark energy is also capable of resolving many of the problems and tensions of ΛCDM, including the cosmological constant problem, the cosmological coincidence problem, and the H₀ and σ₈ tensions, and may account for some effects previously attributed to dark matter. Full article

To elucidate the robustness of the baryon acoustic oscillation (BAO) data measured by the dark energy spectroscopic instrument (DESI) in capturing the dynamical behavior of dark energy, we assess the model dependence of the evidence for dynamical dark energy inferred from the DESI BAO data. While the DESI BAO data slightly tightens the constraints on model parameters and increases the tension between the Chevallier–Polarski–Linder (CPL) model and the $\Lambda$CDM model, we find that the influence of DESI BAO data on the constraint of $w_0$ is small in the SSLCPL model. In comparison to the CPL model, the tension with the $\Lambda$CDM model is reduced for the SSLCPL model, suggesting that the evidence for dynamical dark energy from DESI BAO data is dependent on cosmological models. The inclusion of spatial curvature has little impact on the results in the SSLCPL model. Full article

Recent discoveries of massive galaxies existing in the early universe, as well as apparent anomalies in Ω_m and H₀ at high redshift, have raised sharp new concerns for the ΛCDM model of cosmology. Here, we address these problems by using new solutions for the Einstein field equations of relativistic compact objects originally found by Ni. Applied to the universe, the new solutions imply that the universe’s mass is relatively concentrated in a thick outer shell. The interior space would not have a flat, Minkowski metric, but rather a repulsive gravitational field centered on the origin. This field would induce a gravitational redshift in light waves moving inward from the cosmic shell and a corresponding blueshift in waves approaching the shell. Assuming the Milky Way lies near the origin, within the KBC Void, this redshift would make H₀ appear to diminish at high redshifts and could thus relieve the Hubble tension. The Ni redshift could also reduce or eliminate the requirement for dark energy in the ΛCDM model. The relative dimness of distant objects would instead arise because the Ni redshift makes them appear closer to us than they really are. To account for the CMB temperature–redshift relation and for the absence of a systematic blueshift in stars closer to the origin than the Milky Way, it is proposed that the Ni redshift and blueshift involve exchanges of photon energy with a photonic spacetime. These exchanges in turn form the basis for a cosmic CMB cycle, which gives rise to gravity and an Einsteinian cosmological constant, Λ. Black holes are suggested to have analogous Ni structures and gravity/Λ cycles. Full article

$\mathsf{\Lambda }$CDM tensions are by definition model-dependent; one sees anomalies through the prism of $\mathsf{\Lambda }$CDM. Thus, progress towards tension resolution necessitates checking the consistency of the $\mathsf{\Lambda }$CDM model to localise missing physics either in redshift or scale. Since the universe is dynamical and redshift is a proxy for time, it is imperative to first perform consistency checks involving redshift, then consistency checks involving scale as the next steps to settle the “systematics versus new physics” debate and foster informed model building. We present a review of the hierarchy of assumptions underlying the $\mathsf{\Lambda }$CDM cosmological model and comment on whether relaxing them can address the tensions. We focus on the lowest lying fruit of identifying missing physics through the identification of redshift-dependent $\mathsf{\Lambda }$CDM model fitting parameters. We highlight the recent progress made on $S_8:={\sigma }_8\sqrt{{\mathsf{\Omega }}_{\mathrm{m}}/0.3}$ tension and elucidate how similar progress can be made on $H_0$ tension. Our discussions indicate that $H_0$ tension, equivalently a redshift-dependent $H_0$, and a redshift-dependent $S_8$ imply a problem with the background $\mathsf{\Lambda }$CDM cosmology. Full article

Relaxing the temporal constancy constraint on coupling constants in an expanding universe results in Friedmann equations containing terms that may be interpreted as dark energy and dark matter. When tired light (TL) was considered to complement the redshift due to the expanding universe, the resulting covarying coupling constants (CCC+TL) model not only fit the Type Ia supernovae data as precisely as the ΛCDM model, but also resolved concerns about the angular size of cosmic dawn galaxies observed by the James Webb Space Telescope. The model was recently shown to be compliant with the baryon acoustic oscillation features in the galaxy distribution and the cosmic microwave background (CMB). This paper demonstrates that dark energy and dark matter of the standard ΛCDM model are not arbitrary but can be derived from the CCC approach based on Dirac’s 1937 hypothesis. The energy densities associated with dark matter and dark energy turn out to be about the same in the ΛCDM and the CCC+TL models. However, the critical density in the new model can only account for the baryonic matter in the universe, raising concerns about how to account for observations requiring dark matter. We therefore analyze some key parameters of structure formation and show how they are affected in the absence of dark matter in the CCC+TL scenario. It requires reconsidering alternatives to dark matter to explain observations on gravitationally bound structures. Incidentally, since the CCC models inherently have no dark energy, it has no coincidence problem. The model’s consistency with the CMB power spectrum, BBN element abundances, and other critical observations is yet to be established. Full article

I deduce an exact and analytic Bianchi type I solution of Einstein’s field equations, which generalizes the isotropic ΛCDM universe model to a corresponding model with anisotropic expansion. The main point of the article is to present the anisotropic generalization of the ΛCDM universe model in a way suitable for investigating how anisotropic expansion modifies observable properties of the ΛCDM universe model. Although such generalizations of the isotropic ΛCDM universe model have been considered earlier, they have never been presented in this form before. Several physical properties of the model are pointed out and compared with properties of special cases, such as the isotropic ΛCDM universe model. The solution is then used to investigate the Hubble tension. It has recently been suggested that the cosmic large-scale anisotropy may solve the Hubble tension. I consider those earlier suggestions and find that the formulae of these papers lead to the result that the anisotropy of the cosmic expansion is too small to solve the Hubble tension. Then, I investigate the problem in a new way, using the exact solution of the field equations. This gives the result that the cosmic expansion anisotropy is still too small to solve the Hubble tension in the general Bianchi type I universe with dust and LIVE (Lorentz Invariant Vacuum Energy with a constant energy density, which is represented by the cosmological constant) and anisotropic expansion in all three directions—even if one neglects the constraints coming from the requirement that the anisotropy should be sufficiently small so that it does not have any significant effect upon the results coming from the calculations of the comic nucleosynthesis during the first ten minutes of the universe. If this constraint is taken into account, the cosmic expansion anisotropy is much too small to solve the Hubble tension. Full article

Currently, there is no widely accepted consensus regarding a consistent thermodynamic framework within the special relativity paradigm. However, by postulating that the inverse temperature 4-vector, denoted as $\mathit{\beta }$, is future-directed and time-like, intriguing insights emerge. Specifically, it is demonstrated that the q-dependent Tsallis distribution can be conceptualized as a de Sitterian deformation of the relativistic Maxwell–Jüttner distribution. In this context, the curvature of the de Sitter space-time is characterized by $\sqrt{\Lambda /3}$, where $\Lambda$ represents the cosmological constant within the $\Lambda$CDM standard model for cosmology. For a simple gas composed of particles with proper mass m, and within the framework of quantum statistical de Sitterian considerations, the Tsallis parameter q exhibits a dependence on the cosmological constant given by $q=1+{\ell }_c\sqrt{\Lambda }/\mathfrak{n}$, where ${\ell }_c=\hslash /mc$ is the Compton length of the particle and $\mathfrak{n}$ is a positive numerical factor, the determination of which awaits observational confirmation. This formulation establishes a novel connection between the Tsallis distribution, quantum statistics, and the cosmological constant, shedding light on the intricate interplay between relativistic thermodynamics and fundamental cosmological parameters. Full article

Although the $\Lambda$ Cold Dark Matter model is the most accredited cosmological model, information at high redshifts (z) between type Ia supernovae ($z=2.26$) and the Cosmic Microwave Background ($z=1100$) is crucial to validate this model further. To this end, we have discovered a sample of 1132 quasars up to $z=7.54$ exhibiting a reduced intrinsic dispersion of the relation between ultraviolet and X-ray fluxes, ${\delta }_{\mathrm{F}}=0.22$ vs. ${\delta }_{\mathrm{F}}=0.29$ ($24\%$ less), than the original sample. This gold sample, once we correct the luminosities for selection biases and redshift evolution, enables us to determine the matter density parameter ${\Omega }_M$ with a precision of 0.09. Unprecedentedly, this quasar sample is the only one that, as a standalone cosmological probe, yields such tight constraints on ${\Omega }_M$ while being drawn from the same parent population of the initial sample. Full article

The matter fluctuation parameter ${\sigma }_8$ is, by model construction, degenerate with the growth index $\gamma$. Here, we study the effect on the cosmological parameter constraints by treating each independently from one another, considering ${\sigma }_8$ as a free and non-derived parameter along with a free $\gamma$. We then try to constrain all parameters using three probes that span from deep to local redshifts, namely the CMB spectrum, the growth measurements from redshift space distortions $f{\sigma }_8$, and the galaxy cluster counts. We also aim to assess the impact of this relaxation on the ${\sigma }_8$ tension between its inferred CMB value in comparison to that obtained from local cluster counts. We also propose a more sophisticated correction, along with the classical one, that takes into account the impact of cosmology on the growth measurements when the parameters are varied in the Monte Carlo process, which consist in adjusting the growth to keep the observed power spectrum, integrated over all angles and scales, as invariant with the background evolution. We found by using the classical correction that untying the two parameters does not shift the maximum likelihood of either ${\sigma }_8$ or $\gamma$, but it rather enables larger bounds with respect to when ${\sigma }_8$ is a derived parameter, and that when considering CMB + $f{\sigma }_8$, or when further combining with cluster counts albeit with tighter bounds. Precisely, we obtain ${\sigma }_8=0.809\pm 0.043$ and $\gamma =0.613\pm 0.046$ in agreement with Planck’s constraint for the former and compatible with ΛCDM for the latter but with bounds wide enough to accommodate both values subject to the tensions. Allowing for massive neutrinos does not change the situation much. On the other hand, considering a tiered correction yields ${\sigma }_8=0.734\pm 0.013$ close to ∼1 $\sigma$ for the inferred local values albeit with a growth index of $\gamma =0.636\pm 0.022$ at ∼2 $\sigma$ from its ΛCDM value. Allowing for massive neutrinos in this case yielded ${\sigma }_8=0.756\pm 0.024$, still preferring low values but with much looser constraints on $\gamma =0.549\pm 0.048$ and a slight preference for $\mathsf{\Sigma }{m}_{\nu }\sim 0.19$. We conclude that untying ${\sigma }_8$ and $\gamma$ helps in relieving the discomfort on the former between the CMB and local probes, and that careful analysis should be followed when using data products treated in a model-dependent way. Full article

The primary purpose of this work is the provision of accurate, analytic, evolutionary templates for cosmological parameters and fundamental constants in a dynamical cosmology. A flat quintessence cosmology with a dark energy potential that has the mathematical form of the Higgs potential is the specific cosmology and potential addressed in this work. These templates, based on the physics of the cosmology and potential, are intended to replace those parameterizations currently used to determine the likelihoods of dynamical cosmologies. Acknowledging that, unlike $\Lambda$CDM, the evolutions are dependent on both the specific cosmology and the dark energy potential, the templates are referred to as specific cosmology and potential (SCP) templates. The requirements set for the SCP templates are that they must be accurate, analytic functions of an observable, such as the scale factor or redshift. This is achieved through the utilization of a modified beta function formalism that is based on a physically motivated dark energy potential to calculate the beta function. The methodology developed here is designed to be adaptable to other cosmologies and dark energy potentials. The SCP templates are essential tools in determining the relative likelihoods of a range of dynamical cosmologies and potentials. The ultimate purpose is the determination of whether dark energy is dynamical or static in a quantitative manner. It is suggested that the SCP templates calculated in this work can serve as fiducial dynamical templates in the same manner as $\Lambda$CDM serves for static dark energy. Full article

The standard ΛCDM model, despite its agreement with observational data, still has some issues unaddressed, such as the problem of initial singularity. Solving that problem usually requires modifications of general relativity. However, there appeared the Hořava–Lifshitz (HL) theory of gravity, in which equations governing cosmological evolution include a new term scaling similarly as the dark radiation term in the Friedmann equations, enabling a bounce of the universe instead of initial singularity. This review describes past works on the stability of such a bounce in different formulations of HL theory, an initial detailed balance scenario, and further projectable versions containing higher than quadratic terms to the original action. Full article

Advances in cosmology and astronomical observations have brought to light significant tensions and uncertainties within the current model of cosmology, which assumes a spatially flat Universe and is known as the ΛCDM model. Moreover, the Planck Legacy 2018 release has preferred that the early Universe had a positive curvature with a confidence level more than 99%. This study reports a quantum mechanism that could potentially replace the concept of dark matter/energy by taking into the account the primordial curvature while generating the present-day spatial flatness. The approach incorporates the primordial curvature as the background curvature to extend the field equations into brane-world gravity. It utilizes a new wavefunction of the Universe that propagates in the bulk with respect to the scale factor and curvature radius of the early Universe upon the emission of the cosmic microwave background. The resulting wavefunction yields both positive and negative solutions, revealing the presence of a pair of entangled wavefunctions as a manifestation of the creation of matter and antimatter sides of the Universe. The wavefunction shows a nascent hyperbolic expansion away from early energy in opposite directions followed by a first decelerating expansion phase during the first ~10 Gyr and a subsequent accelerating expansion phase in reverse directions. During the second phase, both Universe sides are free-falling towards each other under gravitational acceleration. The simulation of the predicted background curvature evolution shows that the early curved background caused galaxies to experience external fields, resulting in the fast orbital speed of outer stars. Finally, the wavefunction predicts that the Universe will eventually undergo a rapid contraction phase resulting in a Big Crunch, which reveals a cyclic Universe. Full article