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Our paper introduces a new theoretical framework called the Fractional Einstein–Gauss–Bonnet scalar field cosmology, which has important physical implications. Using fractional calculus to modify the gravitational action integral, we derived a modified Friedmann equation and a modified Klein–Gordon equation. Our research reveals non-trivial solutions associated with exponential potential, exponential couplings to the Gauss–Bonnet term, and a logarithmic scalar field, which are dependent on two cosmological parameters, m and α 0 = t 0 H 0 and the fractional derivative order μ. By employing linear stability theory, we reveal the phase space structure and analyze the dynamic effects of the Gauss–Bonnet couplings. The scaling behavior at some equilibrium points reveals that the geometric corrections in the coupling to the Gauss–Bonnet scalar can mimic the behavior of the dark sector in modified gravity. Using data from cosmic chronometers, type Ia supernovae, supermassive Black Hole Shadows, and strong gravitational lensing, we estimated the values of m and α 0 , indicating that the solution is consistent with an accelerated expansion at late times with the values α 0 = 1.38 ± 0.05 , m = 1.44 ± 0.05 , and μ = 1.48 ± 0.17 (consistent with Ω m , 0 = 0.311 ± 0.016 and h = 0.712 ± 0.007 ), resulting in an age of the Universe t 0 = 19.0 ± 0.7 [Gyr] at 1 σ CL. Ultimately, we obtained late-time accelerating power-law solutions supported by the most recent cosmological data, and we proposed an alternative explanation for the origin of cosmic acceleration other than Λ CDM. Our results generalize and significantly improve previous achievements in the literature, highlighting the practical implications of fractional calculus in cosmology. [ABSTRACT FROM AUTHOR]

We investigate the absolute calibration of the tip of the red giant branch (TRGB) in the Small Magellanic Cloud (SMC) using small amplitude red giant stars (SARGs) classified by the Optical Gravitational Lensing Experiment (OGLE). We show that all stars near the SMC's TRGB are SARGs. Distinguishing older and younger RGs near the tip according to two period–luminosity sequences labeled A and B, we show many similarities among SARG populations of the Large Magellanic Cloud (LMC) and the SMC, along with notable differences. In particular, SMC SARGs have shorter periods due to lower metallicity and smaller amplitudes due to younger ages than LMC SARGs. We discover two period–color relations near the TRGB that span all A-sequence and B-sequence stars in the OGLE-III footprints of the SMC and LMC, and we investigate using periods instead of color for TRGB standardization. Using variability-derived information only, we trace the SMC's age and metallicity gradients and show the core to be populated by younger, more metal-rich RGs. The B-sequence yields the brightest and most accurate calibration (M F814W,syn = −4.057 ± 0.019(stat.) ± 0.029(syst.) mag), which we use to measure the distance modulus difference between the Clouds and investigate metallicity effects. Distance measurements not informed by variability should employ the SARG-based calibration based on all stars near the tip (M F814W,syn = −4.024 ± 0.041(stat.) ± 0.029(syst.) mag). Our work highlights the impact of RG population diversity on TRGB distance measurements. Further study is needed to unravel these effects and improve TRGB standardization. [ABSTRACT FROM AUTHOR]

The equation of state of quantum fluctuations of the gravitational field of the universe depends on H 4 , where H is the Hubble constant. This means that it is invariant with respect to the Wick rotation, i.e., the transition from Lorentzian space-time to Euclidean space-time and vice versa. It is shown that the quantum birth of universes from Euclidean space-time, i.e., from nothing, and their quantum disappearance to nothing (return to Euclidean space-time) by the time the density of the matter filling the universe becomes negligible could be a likely cosmological scenario. On an infinite time axis, this is an endless process of birth and death of universes appearing and disappearing and replacing each other. Within this scenario, our current universe is going to disappear into nothing at z ≤ − 0.68 , i.e., after 18.37 billion years, and the lifetime of our universe and similar universes is about 32 billion years. [ABSTRACT FROM AUTHOR]

The Cepheid AW Per is a component in a multiple system with a long-period orbit. The radial velocities of Griffin cover the 38 yr orbit well. An extensive program of interferometry with the Center for High Angular Resolution Astronomy array is reported here, from which the long-period orbit is determined. In addition, a Hubble Space Telescope high-resolution spectrum in the ultraviolet demonstrates that the companion is itself a binary with nearly equal-mass components. These data combined with a distance from Gaia provide a mass of the Cepheid (primary) of M 1 = 6.79 ± 0.85 M ⊙. The combined mass of the secondary is M S = 8.79 ± 0.50 M ⊙. The accuracy of the mass will be improved after the fourth Gaia data release, expected in approximately two years. [ABSTRACT FROM AUTHOR]

Recent advancements have shown tensions between observations and our current understanding of the Universe. Such observations may include the H 0 tension and massive galaxies at high redshift that are older than traditional galaxy formation models have predict. Since these observations are based on redshift as the primary distance indicator, a bias in the redshift may explain these tensions. While redshift follows an established model, when applied to astronomy it is based on the assumption that the rotational velocity of the Milky Way galaxy relative to the observed galaxies has a negligible effect on redshift. But given the mysterious nature of the physics of galaxy rotation, that assumption needed to be tested. The test was done by comparing the redshift of galaxies rotating in the same direction relative to the Milky Way to the redshift of galaxies rotating in the opposite direction relative to the Milky Way. The results show that the mean redshift of galaxies that rotate in the same direction relative to the Milky Way is higher than the mean redshift of galaxies that rotate in the opposite direction. Additionally, the redshift difference becomes larger as the redshift gets higher. The consistency of the analysis was verified by comparing data collected by three different telescopes, annotated using four different methods, released by three different research teams, and covering both the northern and southern ends of the galactic pole. All the datasets are in excellent agreement with each other, showing consistency in the observed redshift bias. Given the "reproducibility crisis" in science, all the datasets used in this study are publicly available, and the results can be easily reproduced. This observation could be the first direct empirical reproducible observation for the Zwicky's "tired-light" model. [ABSTRACT FROM AUTHOR]

The effect of gravitational particle production of scalar particles on the total effective cosmic energy density (in the era after photon decoupling till the present) is considered. The effect is significant for heavy particles. It is found that gravitational particle production results in an effective increase in the directly measured value of the Hubble constant H 0 , while it does not affect the value of the Hubble constant in the calculation of the number density of baryons at the present time that is used to calculate recombination redshift. This may explain why the Hubble constants determined by local measurements and non-local measurements (such as CMB) are different. This suggests that gravitational particle production may have a non-negligible impact on H 0 tension. [ABSTRACT FROM AUTHOR]

This is a golden age for galaxy formation: Existing and especially new telescopes are providing observations that challenge and illuminate rapidly improving theory and simulations. This review describes the formation of the cosmic web and the structure of the dark matter halos that provide the scaffolding of the Universe. It then summarizes how empirical models, semianalytic models, and hydrodynamic simulations attempt to account for key properties of the galaxy population, including the main sequence of star-forming galaxies, the inefficiency of star formation, the shape evolution and color bimodality of galaxies, and the phenomena that cause galaxies to quench their star formation. It concludes with a summary of observations that have challenged the cosmological constant cold dark matter (ΛCDM) paradigm of galaxy formation—including the Hubble and S8 tensions, bright galaxies in the early Universe, an extragalactic background light mystery, missing satellite galaxies, the diversity of dwarf galaxies, the cusp–core problem, the too-big-to-fail problem, stellar clumps, planes of satellite galaxies, and galaxies without dark matter—and solutions that have been proposed. [ABSTRACT FROM AUTHOR]

The Hubble parameter, H0, is not an univocally defined quantity: It relates redshifts to distances in the near Universe, but it is also a key parameter of the ΛCDM standard cosmological model. As such, H0 affects several physical processes at different cosmic epochs and multiple observables. We have counted more than a dozen H0s that are expected to agree if (a) there are no significant systematics in the data and their interpretation and (b) the adopted cosmological model is correct. With few exceptions (proverbially confirming the rule), these determinations do not agree at high statistical significance; their values cluster around two camps: the low (68 km s1 Mpc1) and high (73 km s1 Mpc1) camps. It appears to be a matter of anchors. The shape of the Universe expansion history agrees with the model; it is the normalizations that disagree. Beyond systematics in the data/analysis, if the model is incorrect, there are only two viable ways to "fix" it: by changing the early time (z ≳ 1,100) physics and, thus, the early time normalization or by a global modification, possibly touching the model's fundamental assumptions (e.g., homogeneity, isotropy, gravity). None of these three options has the consensus of the community. The research community has been actively looking for deviations from ΛCDM for two decades; the one we might have found makes us wish we could put the genie back in the bottle. [ABSTRACT FROM AUTHOR]

In this Editorial to the Special Issue "The Friedmann Cosmology: A Century Later", we consider an outstanding character of Friedmann's prediction of Universe expansion, which laid the foundation of modern cosmology. The list of the main discoveries made in cosmology during the last one hundred years is followed by a formulation of the standard cosmological model. The articles contributing to the Special Issue are considered in relation to this model, and to several alternative theoretical approaches. Special attention is paid to unresolved problems, such as the nature of dark matter and dark energy, Hubble tension and the pre-inflationary stage of the Universe evolution. The conclusion is made that astrophysics and cosmology are on the threshold of new fundamental discoveries. [ABSTRACT FROM AUTHOR]

We investigate a coupled quintessence cosmological model in which a dark-energy scalar field with an exponential potential interacts directly with a dark-matter fluid through a dissipative term inspired by warm inflation. The evolution equations of this model give rise to a three-dimensional dynamical system for which a thorough qualitative analysis is performed for all values of the relevant parameters. We find that the model is able to replicate the observed sequence of late-time cosmological eras, namely, a long enough matter-dominated era followed by a present era of accelerated expansion. In situations where there is a significant transfer of energy from dark energy to dark matter, temporary scaling-type solutions may arise, but, asymptotically, all solutions are dominated by dark energy. [ABSTRACT FROM AUTHOR]

Λ CDM tensions are by definition model-dependent; one sees anomalies through the prism of Λ CDM. Thus, progress towards tension resolution necessitates checking the consistency of the Λ 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 Λ 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 Λ CDM model fitting parameters. We highlight the recent progress made on S 8 : = σ 8 Ω 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 Λ CDM cosmology. [ABSTRACT FROM AUTHOR]

We perform new measurements of the expansion rate and the sound horizon at the end of the baryon decoupling, and derive constraints on cosmic key parameters in the framework of the Λ CDM model, wCDM model, non-flat Λ CDM model and the phenomenological emergent dark energy (PEDE) model. We keep r d and H 0 completely free, and use the recent Dark Energy Spectroscopic Instrument (DESI) Year 1 and Dark Energy Survey (DES) Year 6 BAO measurements in the effective redshift range 0.3 < z < 2.33 , combined with the compressed form of the Pantheon sample of Type Ia supernovae, the latest 34 observational H (z) measurements based on the differential age method, and the recent H 0 measurement from SH0ES 2022 as an additional Gaussian prior. Combining BAO data with the observational H (z) measurements, and the Pantheon SNe Ia data, we obtain H 0 = 69.70 ± 1.11 km s − 1 Mpc − 1 , r d = 147.14 ± 2.56 Mpc in flat Λ CDM model, H 0 = 70.01 ± 1.14 km s − 1 Mpc − 1 , r d = 146.97 ± 2.45 Mpc in PEDE model. The spatial curvature is Ω k = 0.023 ± 0.025 , and the dark energy equation of state is w = − 1.029 ± 0.051 , consistent with a cosmological constant. We apply the Akaike information and the Bayesian information criterion test to compare the four models, and see that the PEDE model performs better. [ABSTRACT FROM AUTHOR]

We consider a dynamic scenario for characterizing the late Universe evolution, aiming to mitigate the Hubble tension. Specifically, we consider a metric f (R) gravity in the Jordan frame which is implemented to the dynamics of a flat isotropic Universe. This cosmological model incorporates a matter creation process, due to the time variation of the cosmological gravitational field. We model particle creation by representing the isotropic Universe (specifically, a given fiducial volume) as an open thermodynamic system. The resulting dynamical model involves four unknowns: the Hubble parameter, the non-minimally coupled scalar field, its potential, and the energy density of the matter component. We impose suitable conditions to derive a closed system for these functions of the redshift. In this model, the vacuum energy density of the present Universe is determined by the scalar field potential, in line with the modified gravity scenario. Hence, we construct a viable model, determining the form of the f (R) theory a posteriori and appropriately constraining the phenomenological parameters of the matter creation process to eliminate tachyon modes. Finally, by analyzing the allowed parameter space, we demonstrate that the Planck evolution of the Hubble parameter can be reconciled with the late Universe dynamics, thus alleviating the Hubble tension. [ABSTRACT FROM AUTHOR]

Recently Tsallis cosmology has been presented as a novel proposal for alleviating both H 0 and σ 8 tensions. Hence a universe filled with matter and radiation as perfect fluids and considering the Tsallis entropy is confronted using recent cosmological measurements coming from cosmic chronometers, type Ia supernovae, hydrogen II galaxies, quasars, and baryon acoustic oscillations. Following a Bayesian Markov Chain Monte Carlo analysis and combining the samples, we constrain the main characteristic parameters α = 1. 031 - 0.051 + 0.054 and δ = 1. 005 - 0.001 + 0.001 where the uncertainties are 1 σ confidence level. Additionally, we estimate the current deceleration parameter q 0 = - 0. 530 - 0.017 + 0.018 , the deceleration-acceleration transition redshift z T = 0. 632 - 0.028 + 0.028 and the age of the universe τ U = 12. 637 - 0.066 + 0.067 Gyrs which are in agreement with the standard cosmology (Λ CDM) within 1.5 σ . Furthermore, we find that the dark energy equation of state is consistent with both phantom and quintessence behaviors within 1 σ in the past and converging to Λ CDM in the future. Additionally, we find agreement values of H 0 within 1 σ with the SH0ES values when the CMB distance priors are added to the analysis, suggesting that H 0 tension could be alleviated. Finally, Tsallis cosmology is preferred over Λ CDM by the combined data that motives further studies at the perturbation level. [ABSTRACT FROM AUTHOR]

In the context of the minimally extended varying speed of light (meVSL) model, both the absolute magnitude and the luminosity distance of type Ia supernovae (SNe Ia) deviate from those predicted by general relativity (GR). Using data from the Pantheon+ survey, we assess the plausibility of various dark energy models within the framework of meVSL. Both the constant equation of state (EoS) of the dark energy model (ω CDM) and the Chevallier–Polarski–Linder (CPL) parameterization model ( ω = ω 0 + ω a (1 − a) ) indicate potential variations in the cosmic speed of light at the 1 − σ confidence level. For Ω m 0 = 0.30 , 0.31 , and 0.32 with (ω 0 , ω a) = (− 1 , 0) , the 1 − σ range of c ˙ 0 / c 0 (10 − 13 yr − 1) is (−8.76, −0.89), (−11.8, 3.93), and (−14.8, −6.98), respectively. Meanwhile, the 1 − σ range of c ˙ 0 / c 0 (10 − 12 yr − 1) for CPL dark energy models with − 1.05 ≤ ω 0 ≤ − 0.95 and 0.28 ≤ Ω m 0 ≤ 0.32 is (−6.31, −2.98). The value of c at z = 3 can exceed that of the present by 0.2∼3% for ω CDM models and 5∼13% for CPL models. Additionally, for viable models except for the CPL model with Ω m 0 = 0.28 , we find − 25.6 ≤ G ˙ 0 / G 0 (10 − 12 yr − 1) ≤ − 0.36 . For this particular model, we obtain an increasing rate of the gravitational constant within the range 1.65 ≤ G ˙ 0 / G 0 (10 − 12 yr − 1) ≤ 3.79 . We obtain some models that do not require dark matter energy density through statistical interpretation. However, this is merely an effect of the degeneracy between model parameters and energy density and does not imply that dark matter is unnecessary. [ABSTRACT FROM AUTHOR]

In this work, we explore new constraints on phantom scalar field cosmologies with a scalar field employing early-time catalogs related to CMB measurements, along with the local standard observables, like Supernovae Type Ia (SNIa), H (z) measurements (Cosmick clocks), and Baryon Acoustic Oscillation (BAO) baselines. In particular, we studied a tracker phantom field with hyperbolic polar coordinates that have been proposed in the literature. The main goal is to obtain precise cosmological constraints for H 0 and σ 8 , in comparison to other constructions that present tension in early cosmological parameters. Our results show that phantom scalar field cosmologies have a reduced statistical tension on H 0 that it is less than 3 σ using model-independent CMB catalogs as SPT-3G+WMAP9 and ACTPol DR-4+WMAP9 baselines. This suggests that these models, using a different phantom potential, might address the Hubble constant problem and reduce the systematics involved. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

At least two relics of the Big Bang have survived: the cosmological microwave background (CMB) and the cosmological neutrino background (C ν B). Being the second most abundant particle in the universe, the neutrino has a significant impact on its evolution from the Big Bang to the present day. Neutrinos affect the following cosmological processes: the expansion rate of the universe, its chemical and isotopic composition, the CMB anisotropy and the formation of the large-scale structure of the universe. Another relic neutrino background is theoretically predicted, it consists of non-equilibrium antineutrinos of Primordial Nucleosynthesis arising as a result of the decay of neutrons and tritium nuclei. Such antineutrinos are an indicator of the baryon asymmetry of the universe. In addition to experimentally detectable active neutrinos, the existence of sterile neutrinos is theoretically predicted to generate neutrino masses and explain their oscillations. Sterile neutrinos can also solve such cosmological problems as the baryonic asymmetry of the universe and the nature of dark matter. The recent results of several independent experiments point to the possibility of the existence of a light sterile neutrino. However, the existence of such a neutrino is inconsistent with the predictions of the Standard Cosmological Model. The inclusion of a non-zero lepton asymmetry of the universe and/or increasing the energy density of active neutrinos can eliminate these contradictions and reconcile the possible existence of sterile neutrinos with Primordial Nucleosynthesis, the CMB anisotropy, and also reduce the H0-tension. In this brief review, we discuss the influence of the physical properties of active and sterile neutrinos on the evolution of the universe from the Big Bang to the present day. [ABSTRACT FROM AUTHOR]

We present the results of a comparison between different methods to estimate the power of relativistic jets from active galactic nuclei (AGN). We selected a sample of 32 objects (21 flat-spectrum radio quasars, 7 BL Lacertae objects, 2 misaligned AGN, and 2 changing-look AGN) from the very large baseline array (VLBA) observations at 43 GHz of the Boston University blazar program. We then calculated the total, radiative, and kinetic jet power from both radio and high-energy gamma-ray observations, and compared the values. We found an excellent agreement between the radiative power calculated by using the Blandford and Königl model with 37 or 43 GHz data and the values derived from the high-energy γ -ray luminosity. The agreement is still acceptable if 15 GHz data are used, although with a larger dispersion, but it improves if we use a constant fraction of the γ -ray luminosity. We found a good agreement also for the kinetic power calculated with the Blandford and Königl model with 15 GHz data and the value from the extended radio emission. We also propose some easy-to-use equations to estimate the jet power. [ABSTRACT FROM AUTHOR]

Holographic principles have proven to be a very interesting approach towards dealing with the issues of the late-time acceleration of the universe, which has resulted in a great amount of work on holographic dark energy models. We consider one such very interesting holographic scenario, namely the Tsallis Holographic dark energy model, and consider an ansatz based approach to such models. We consider three cosmological scenarios in such models, namely those with viscous, non-viscous, and Chaplygin gas scenarios, discussing various crucial aspects related to these models. We discuss various crucial properties of the Tsallis model in such scenarios and see how the phantom divide is crossed in each case, but it is only the Chaplygin gas models which provide a better view on stability issues.The symmetry property of the theory presented in the article is the assumption that space is isotropic. Using bulk viscosity instead of shear viscosity reflects spatial isotropy. [ABSTRACT FROM AUTHOR]

A critical discussion on the H 0 Hubble constant tension is presented by considering both early and late-type observations. From recent precise measurements, discrepancies emerge when comparing results for some cosmological quantities obtained at different redshifts. We highlight the most relevant measurements of H 0 and propose potential ideas to solve its tension. These solutions concern the exploration of new physics beyond the Λ CDM model or the evaluation of H 0 by other methods. In particular, we focus on the role of the look-back time. [ABSTRACT FROM AUTHOR]

We consider f (R , T) modified theories of gravity in the context of string-theory-inspired dilaton gravity. We deal with a specific model that under certain conditions describes the late time Universe in accord with observational data in modern cosmology and addresses the H 0 tension. This is done by exploring the space of parameters made out of those coming from the modified gravity and dilatonic charge sectors. We employ numerical methods to obtain several important observable quantities. [ABSTRACT FROM AUTHOR]

Recent puzzling observations, such as the H 0 tension, large-scale anisotropies, and massive disk galaxies at high redshifts, have been challenging the standard cosmological model. While one possible explanation is that the standard model is incomplete, other theories are based on the contention that the redshift model as a distance indicator might be biased. These theories can explain the recent observations, but they are challenged by the absence of a direct empirical reproducible observation that the redshift model can indeed be inconsistent. Here, I describe a simple experiment that shows that the spectra of galaxies depend on their rotational velocity relative to the rotational velocity of the Milky Way. Moreover, it shows that the redshift of galaxies that rotate in the opposite direction relative to the Milky Way is significantly smaller compared with the redshift of galaxies that rotate in the same direction relative to the Milky Way (p < 0.006). Three different datasets were used independently, each one was prepared in a different manner, and all of them showed similar redshift bias. A fourth dataset of galaxies from the Southern Galactic pole was also analyzed and shows similar results. All four datasets are publicly available. While a maximum average z difference of ∼0.012 observed with galaxies of relatively low redshift (z < 0.25) is not extreme, the bias is consistent and canpotentially lead to explanations to puzzling observations such as the H 0 tension. [ABSTRACT FROM AUTHOR]

Scalar field ϕ CDM models provide an alternative to the standard Λ CDM paradigm, while being physically better motivated. Dynamical scalar field ϕ CDM models are divided into two classes: the quintessence (minimally and non-minimally interacting with gravity) and phantom models. These models explain the phenomenology of late-time dark energy. In these models, energy density and pressure are time-dependent functions under the assumption that the scalar field is described by the ideal barotropic fluid model. As a consequence of this, the equation of state parameter of the ϕ CDM models is also a time-dependent function. The interaction between dark energy and dark matter, namely their transformation into each other, is considered in the interacting dark energy models. The evolution of the universe from the inflationary epoch to the present dark energy epoch is investigated in quintessential inflation models, in which a single scalar field plays a role of both the inflaton field at the inflationary epoch and of the quintessence scalar field at the present epoch. We start with an overview of the motivation behind these classes of models, the basic mathematical formalism, and the different classes of models. We then present a compilation of recent results of applying different observational probes to constraining ϕ CDM model parameters. Over the last two decades, the precision of observational data has increased immensely, leading to ever tighter constraints. A combination of the recent measurements favors the spatially flat Λ CDM model but a large class of ϕ CDM models is still not ruled out. [ABSTRACT FROM AUTHOR]

This paper explores the fundamental cosmological principle, with a specific focus on the homogeneity and isotropy assumptions inherent in the Friedmann model that underpins the standard model. We propose a modified redshift model that is based on the spatial distribution of luminous matter, examining three key astronomical quantities: light intensity, number density, and the redshift of galaxies. Our analysis suggests that the model can account for cosmic accelerated expansion without the need for dark energy in the equations. Both simulations and analytical solutions reveal a unique pattern in the formation and evolution of cosmic structures, particularly in galaxy formation. This pattern shows a significant burst of activity between redshifts 0 < z < 0.4, which then progresses rapidly until approximately z ≈ 0.9, indicating that the majority of cosmic structures were formed during this period. Subsequently, the process slows down considerably, reaching a nearly constant rate until around z ≈ 1.6, after which a gradual decline begins. We also observe a distinctive redshift transition around z ≈ 0.9 before the onset of dark-matter-induced accelerated expansion. This transition is directly related to the matter density and is dependent on the geometry of the universe. The model's ability to explain cosmic acceleration without requiring fine tuning of the cosmological constant highlights its novelty, providing a fresh perspective on the dynamic evolution of the universe. [ABSTRACT FROM AUTHOR]

The discovery of the Universe's late-time acceleration and dark energy has led to a great deal of research into cosmological singularities, and in this brief review, we discuss all the prominent developments in this field for the best part of the last two decades. We discuss the fundamentals of spacetime singularities, after which we discuss in detail all the different forms of cosmological singularities that have been discovered in recent times. We then address methods and techniques to avoid or moderate these singularities in various theories and discuss how these singularities can also occur in non-conventional cosmologies. We then discuss a useful dynamical systems approach to deal with these singularities and finish up with some outlooks for the field. We hope that this work serves as a good resource to anyone who wants to update themselves with the developments in this very exciting area. [ABSTRACT FROM AUTHOR]

We present the X-ray spectral analysis of two complementary sets of intermediate Seyfert galaxies (ISs). Analyzing X-ray data, we estimate the hydrogen abundance N H and test its connection with the [O III] luminosity acquired from optical observations. The results confirm the conclusions drawn in a previous study concerning the lack of a direct correlation between the obscuration measure ( N H ) and the intrinsic characteristics of the active nuclei ([O III] luminosity). Instead, we validate the existence of a correlation between the Seyfert type and the N H parameter, employing a separation threshold of approximately 10 22 atoms cm − 2 . Simultaneously, our findings align with prior research, corroborating the relationship between X-ray luminosity and the [O III] luminosity. [ABSTRACT FROM AUTHOR]

The Hubble tension in cosmology is not showing signs of alleviation and thus, it is important to look for alternative approaches to it. One such example would be the eventual detection of a time delay between simultaneously emitted high-energy and low-energy photons in gamma-ray bursts (GRB). This would signal a possible Lorentz Invariance Violation (LIV) and in the case of non-zero quantum gravity time delay, it can be used to study cosmology as well. In this work, we use various astrophysical datasets (BAO, Pantheon Plus and the CMB distance priors), combined with two GRB time delay datasets with their respective models for the intrinsic time delay. Since the intrinsic time delay is considered the largest source of uncertainty in such studies, finding a better model is important. Our results yield as quantum gravity energy bound E Q G ≥ 10 17 GeV and E Q G ≥ 10 18 GeV respectively. The difference between standard approximation (constant intrinsic lag) and the extended (non-constant) approximations is minimal in most cases we conside. However, the biggest effect on the results comes from the prior on the parameter c H 0 r d , emphasizing once again that at current precision, cosmological datasets are the dominant factor in determining the cosmology. We estimate the energies at which cosmology gets significantly affected by the time delay dataset. [ABSTRACT FROM AUTHOR]

Although the Λ 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, δ F = 0.22 vs. δ 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 Ω 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 Ω M while being drawn from the same parent population of the initial sample. [ABSTRACT FROM AUTHOR]

The f(R, T) gravity models, for which R is the Ricci scalar and T is the trace of the energy–momentum tensor, elevate the degrees of freedom of the renowned f(R) theories, by making the Einstein field equations of the theory to also depend on T. While such a dependence can be motivated by quantum effects, the existence of imperfect or extra fluids, or even a cosmological "constant" which effectively depends on T, the formalism can truly surpass some deficiencies of f(R) gravity. As the f(R, T) function is arbitrary, several parametric models have been proposed ad hoc in the literature and posteriorly confronted with observational data. In the present article, we use gaussian process to construct an f (R , T) = R + f (T) model. To apply the gaussian process we use a series of measurements of the Hubble parameter. We then analytically obtain the functional form of the function. By construction, this form, which is novel in the literature, is well-adjusted to cosmological data. In addition, by extrapolating our reconstruction to redshift z = 0 , we were able to constrain the Hubble constant value to H 0 = 69.97 ± 4.13 km s - 1 Mpc - 1 with 5 % precision. Lastly, we encourage the application of the functional form herewith obtained to other current problems of observational cosmology and astrophysics, such as the rotation curves of galaxies. [ABSTRACT FROM AUTHOR]

While the standard model accurately describes data at the electroweak scale without the inclusion of gravity, beyond the standard model, physics is increasingly intertwined with gravitational phenomena and cosmology. Thus, the gravity-mediated breaking of supersymmetry in supergravity models leads to sparticle masses, which are gravitational in origin, observable at TeV scales and testable at the LHC, and supergravity also provides a candidate for dark matter, a possible framework for inflationary models and for models of dark energy. Further, extended supergravity models and string and D-brane models contain hidden sectors, some of which may be feebly coupled to the visible sector, resulting in heat exchange between the visible and hidden sectors. Because of the couplings between the sectors, both particle physics and cosmology are affected. The above implies that particle physics and cosmology are intrinsically intertwined in the resolution of essentially all of the cosmological phenomena, such as dark matter and dark energy, and in the resolution of cosmological puzzles, such as the Hubble tension and the EDGES anomaly. Here, we give a brief overview of the intertwining and its implications for the discovery of sparticles, as well as the resolution of cosmological anomalies and the identification of dark matter and dark energy as major challenges for the coming decades. [ABSTRACT FROM AUTHOR]

Cosmological parameters are constrained by a wide variety of observations. We examine the concordance diagram for modern measurements of the Hubble constant, the shape parameter from the large-scale structure, the cluster baryon fraction, and the age of the universe, all from non-CMB data. There is good agreement for H 0 = 73.24 ± 0.38 km s − 1 Mpc − 1 and Ω m = 0.237 ± 0.015 . This concordance value is indistinguishable from the WMAP3 cosmology but is not consistent with that of Planck: there is a tension in Ω m as well as H 0 . These tensions have emerged as progressively higher multipoles have been incorporated into CMB fits. This temporal evolution is suggestive of a systematic effect in the analysis of CMB data at fine angular scales and may be related to the observation of unexpectedly massive galaxies at high redshift. These are overabundant relative to Λ CDM predictions by an order of magnitude at z > 7 . Such massive objects are anomalous and could cause gravitational lensing of the surface of last scattering in excess of the standard calculation made in CMB fits, potentially skewing the best-fit cosmological parameters and contributing to the Hubble tension. [ABSTRACT FROM AUTHOR]

This document is a special issue on quantum field theory, covering various topics within the field. It includes investigations on the properties of vacuum models, quantum theories with broken Lorentz symmetry, thermodynamics of Yang-Mills theories, and the emergence of the Dirac equation for classical monopoles. The issue also contains reviews on nonperturbative approaches to QCD and Clifford algebras. The author emphasizes the importance of understanding nonperturbative ground states in pure Yang-Mills theories and the need for a theoretical framework beyond the Standard Model of Particle Physics. The document explores the interrelation between Yang-Mills theory and gravitation, suggesting that studying elementary particles can provide insights into the microstructure of gravitational solitons like black holes. It also discusses the potential for nonperturbative correspondence between gravity and Yang-Mills theory, as well as the role of Yang-Mills thermodynamics in cosmological models. The document briefly mentions critical phenomena in conformal quantum field theories and the research field of symmetric mass generation. [Extracted from the article]

Recently, many researchers have been studying the visualization of images and the recognition of objects by estimating photons under photon-starved conditions. Conventional photon-counting imaging techniques estimate photons by way of a statistical method using Poisson distribution in all image areas. However, Poisson distribution is temporally and spatially independent, and the reconstructed image has a random noise in the background. Random noise in the background may degrade the quality of the image and make it difficult to accurately recognize objects. Therefore, in this paper, we apply photon-counting imaging technology only to the area where the object is located to eliminate the noise in the background. As a result, it can be seen that the image quality using the proposed method is better than that of the conventional method and the object recognition rate is also higher. Optical experiments were conducted to prove the denoising performance of the proposed method. In addition, we used the structure similarity index measure (SSIM) as a performance metric. To check the recognition rate of the object, we applied the YOLOv5 model. Finally, the proposed method is expected to accelerate the development of astrophotography and medical imaging technologies. [ABSTRACT FROM AUTHOR]

One of main sources of uncertainty in modern cosmology is the present rate of the universe's expansion, H0, called the Hubble constant. Once again, different observational techniques bring about different results, causing new "Hubble tension". In the present work, we review the historical roots of the Hubble constant from the beginning of the twentieth century, when modern cosmology originated, to the present. We develop the arguments that gave rise to the importance of measuring the expansion of the Universe and its discovery, and we describe the different pioneering works attempting to measure it. There has been a long dispute on this matter, even in the present epoch, which is marked by high-tech instrumentation and, therefore, in smaller uncertainties in the relevant parameters. It is, again, currently necessary to conduct a careful and critical revision of the different methods before one invokes new physics to solve the so-called Hubble tension. [ABSTRACT FROM AUTHOR]