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There is growing evidence that the net acceleration of the Universe over its entire history is essentially zero. This finding is critical in light of a recent examination of the Friedmann–Lemaître–Robertson–Walker (FLRW) metric using the local flatness theorem (LFT) in general relativity, which argues that FLRW is consistent with the principle of equivalence only if the total energy density ρ\rho and pressure pp satisfy the zero active mass condition, ρ+3p=0\rho +3p=0. This equation-of-state produces zero acceleration, and significantly mitigates the growing tension between lambda cold dark matter (Λ\Lambda CDM) and the ever-improving observations. This article takes an alternative approach to this critical issue and directly tests the expansion rate predicted by the standard model against the requirements of the LFT. It demonstrates that Λ\Lambda CDM simply does not satisfy the principle of equivalence. Some of the many important consequences of this outcome are discussed in the conclusions.

Recent attempts at measuring the variation of c using an assortment of standard candles and the redshift-dependent Hubble expansion rate inferred from the currently available catalogue of cosmic chronometers have tended to show that the speed of light appears to be constant, at least up to z ∼ 2. A notable exception is the use of high-redshift ultraviolet + X-ray quasars, whose Hubble diagram seems to indicate an ∼2.7σ deviation of c from its value c 0 (≡ 2.99792458 × 1010 cm s−1) on Earth. We show in this paper, however, that this anomaly is due to an error in the derived relation between the luminosity distance, D L, and H (z) when c is allowed to vary with redshift, and an imprecise calibration of the quasar catalogue. When these deficiencies are addressed correctly, one finds that c / c 0 = 0.95 ± 0.14 in the redshift range 0 ≲ z ≲ 2, fully consistent with zero variation within the measurement errors. [ABSTRACT FROM AUTHOR]

Momentum is characterized in terms of inertial mass for particles moving at less than the speed of light, but entirely in terms of their energy for those lacking inertia. Does this difference suggest a physically distinct origin of momentum in the two cases and, if so, what is actually being conserved in interactions involving both types of particle? In this paper, we consider a recently proposed gravitational origin for rest-mass energy to demonstrate that a single definition of momentum applies to all particles, massless or otherwise. When introduced into this description, inertial mass is merely a surrogate for the particle's 'free' energy, but does not imply an origin of momentum different from that of particles without mass. [ABSTRACT FROM AUTHOR]

Studies of the Universe's transition to smoothness in the context of Lambda cold dark matter (ΛCDM) have all pointed to a transition radius no larger than ∼300 Mpc. These are based on a broad array of tracers for the matter power spectrum, including galaxies, clusters, quasars, the Ly-α forest, and anisotropies in the cosmic microwave background. It is therefore surprising, if not anomalous, to find many structures extending out over scales as large as ∼2 Gpc, roughly an order of magnitude greater than expected. Such a disparity suggests that new physics may be contributing to the formation of large-scale structure, warranting a consideration of the alternative Friedmann–Lemaître–Robertson–Walker cosmology known as the R h = ct universe. This model has successfully eliminated many other problems in ΛCDM. In this paper, we calculate the fractal (or Hausdorff) dimension in this cosmology as a function of distance, showing a transition to smoothness at ∼2.2 Gpc, fully accommodating all of the giant structures seen thus far. This outcome adds further observational support for R h = ct over the standard model. [ABSTRACT FROM AUTHOR]

The energy conditions in general relativity are introduced to establish powerful theorems without having to restrict their applicability to specific choices of the stress‐energy tensor. They are famously invoked, e.g., to prove the singularity theorems of Penrose and Hawking, but have also been applied elsewhere, including various tests of certain cosmological theories. These conditions have become somewhat controversial, however, because they appear to be violated by commonly accepted scenarios, such as inflation shortly after the Big Bang and late‐time acceleration of the cosmic expansion. But accommodating these processes by abandoning all of the energy conditions will promote other disquieting possibilities, including the breakdown of causality with traversable wormholes and closed timeloops. This paper advocates for the opposite viewpoint, demonstrating that the 'numen' scalar field, derived from the zero active mass condition in general relativity, satisfies all of the energy conditions in the early Universe. This unique feature among scalar fields adds to its success in accounting for the observed properties of the cosmic microwave background better than its inflationary counterpart. Specifically, numen's complete consistency with all of the energy conditions, and inflation's violation of at least one of them, provides additional justification for theoretically favoring the former over the latter. [ABSTRACT FROM AUTHOR]

The evidence in favor of a Universe expanding at a constant rate, in contrast to the various episodes of deceleration and acceleration expected in the standard model, has been accumulating for over a decade now. In recent years, this inference has been strengthened by a study of the Friedmann–Lemaître–Robertson–Walker (FLRW) metric in relation to Einstein's principle of equivalence. This earlier work concluded that the choice of lapse function gtt = 1 characterizing the FLRW solution to Einstein's equations is inconsistent with any kind of accelerated cosmic expansion. In this paper, we demonstrate and confirm this important result by directly testing the self-consistency of four well-known FLRW cosmologies. These include the Milne universe, de Sitter space, the Lanczos universe, and the Rh = ct model. We show that only the constantly expanding models (Milne and Rh = ct) are consistent with the principle of equivalence, while de Sitter and Lanczos fail the test. We discuss some of the many consequences of this conclusion. [ABSTRACT FROM AUTHOR]

The so-called impossibly early galaxy problem, first identified via the Hubble Space Telescope 's observation of galaxies at redshifts z > 10, appears to have been exacerbated by the more recent JWST discovery of galaxy candidates at even higher redshifts (z ∼ 17) which, however, are yet to be confirmed spectroscopically. These candidates would have emerged only ∼230 Myr after the big bang in the context of Lambda cold dark matter (ΛCDM), requiring a more rapid star formation in the earliest galaxies than appears to be permitted by simulations adopting the concordance model parameters. This time-compression problem would therefore be inconsistent with the age–redshift relation predicted by ΛCDM. Instead, the sequence of star formation and galaxy assembly would confirm the timeline predicted by the R h = ct universe, a theoretically advanced version of ΛCDM that incorporates the 'zero active mass' condition from general relativity. This model has accounted for many cosmological data better than ΛCDM, and eliminates all of its inconsistencies, including the horizon and initial entropy problems. The latest JWST discoveries at z ≳ 14, if confirmed, would add further support to the idea that the R h = ct universe is favoured by the observations over the current standard model. [ABSTRACT FROM AUTHOR]

The sample of time-delay gravitational lenses appropriate for studying the geometry of the Universe continues to grow as dedicated campaigns, such as the Dark Energy Survey, the (Very Large Telescope) VLT Survey Telescope (VST) ATLAS survey, and the Large Synoptic Survey Telescope, complete their census of high-redshift sources. This catalogue now includes hundreds of strong lensing systems, at least 31 of which have reasonably accurate time-delay measurements. In this paper, we use them to compare the predictions of two competing Friedmann–Lemaître–Robertson–Walker models: flat Lambda cold dark matter (ΛCDM), characterized by two adjustable parameters (H 0 and Ωm), and the R h = ct universe (with H 0 as the single free variable). Over the past decade, the latter has accounted for the data better than the standard model, most recently the emergence of well-formed galaxies discovered by JWST at cosmic dawn. Here, we show that the current sample of time-delay lenses favours R h = ct with a likelihood of ∼ |$84{{\ \rm per\ cent}}$| versus ∼ |$16{{\ \rm per\ cent}}$| for the standard model. This level of accuracy will greatly improve as the ongoing surveys uncover many thousands of additional lens systems over the next several years. [ABSTRACT FROM AUTHOR]

Modern cosmology is broadly based on the Cosmological principle, which assumes homogeneity and isotropy as its foundational pillars. Thus, there is not much debate about the metric (i.e., Friedmann-Lemaître-Robertson-Walker; FLRW) one should use to describe the cosmic spacetime. But Einstein's equations do not unilaterally constrain the constituents in the cosmic fluid, which directly determine the expansion factor appearing in the metric coefficients. As its name suggests, ΛCDM posits that the energy density is dominated by a blend of dark energy (typically a cosmological constant, Λ), cold dark matter (and a "contamination" of baryonic matter) and radiation. Many would assert that we have now reached the age of "precision" cosmology, in which measurements are made merely to refine the excessively large number of free parameters characterizing its empirical underpinnings. But this mantra glosses over a growing body of embarrassingly significant failings, not just "tension" as is sometimes described, as if to somehow imply that a resolution will eventually be found. In this paper, we take a candid look at some of the most glaring conflicts between the standard model, the observations, and several foundational principles in quantum mechanics, general relativity and particle physics. One cannot avoid the conclusion that the standard model needs a complete overhaul in order to survive. [ABSTRACT FROM AUTHOR]

We consider several well-known f (R) cosmological models and constrain their parameters, namely the deviation parameter b and the cosmological parameters Ωm and h. We first obtain analytical approximations for the Hubble rate H (z) and the luminosity distance dL (z) in terms of these parameters, and then test these against the observational expansion rate derived from cosmic chronometers (CCs) and the distance modulus in the H  ii galaxy Hubble diagram, obtained in a model-independent way using Gaussian processes. We first optimize the models based solely on the CCs and then repeat this process with a joint analysis using both the CCs and H  ii galaxies. [ABSTRACT FROM AUTHOR]

The absence of large-angle correlations in the temperature of the cosmic microwave background (CMB), confirmed by three independent satellite missions, creates significant tension with the standard model of cosmology. Previous work has shown, however, that a truncation, k min , of the primordial power spectrum comprehensively resolves the anomaly and the missing power at ℓ ≲ 5 (the low multipoles). Since this cutoff is consistent with the hypothesized delay of inflation well beyond the Planck time, we are strongly motivated to consider its possible impact on other observational signatures. In this Letter , we analyze and predict its influence on the most revealing probe awaiting measurement by upcoming missions—the B-mode polarization of the CMB, whose accurate determination should greatly impact the inflationary picture. We highlight the quantitative power of this discriminant by specifically considering the LiteBIRD mission, predicting the effect of k min on both the angular power spectrum and the angular correlation function of the B-mode, for a range of tensor-to-scalar ratios, r. While its impact on the latter appears to be negligible, k min should have a very pronounced effect on the former. We show that for r = 0.036 , k min 's impact on C ℓ B B at low ℓ 's should be easily detectable by LiteBIRD, but will be largely hidden by the total uncertainty of the measurement if r ≲ 0.02. [ABSTRACT FROM AUTHOR]

The supermassive black hole at the galactic center has been studied and may be the most compelling supermassive black hold candidate with weight at a little more than 2.6 mil suns. The latest observational results and the physical interpretation of the most intriguing object in the region, the compact radio source Sgr A(super.asterisk) are summarized. This source is thought to be the radiative manifestation of the supermassive black hole.

The Friedmann–Lemaître–Robertson–Walker (FLRW) metric used to describe the cosmic spacetime is based on the cosmological principle, which assumes homogeneity and isotropy throughout the Universe. It also adopts free-fall conditions via the selection of a constant lapse function, g t t = 1 , regardless of whether or not the chosen energy–momentum tensor T α β produces an accelerated expansion. This is sometimes justified by arguing that one may shift the gauge, if necessary, transforming the time d t to a new coordinate d t ′ ≡ g t t d t , thereby re-establishing a unitary value for g t ′ t ′ . Previously, we have demonstrated that this approach is inconsistent with the Friedmann equations derived using comoving coordinates. In this paper, we advance this discussion significantly by using the Local Flatness Theorem in general relativity to prove that g t t in FLRW is inextricably dependent on the expansion dynamics via the expansion factor a (t) , which itself depends on the equation-of-state in T α β . One is therefore not free to choose g t t arbitrarily without ensuring its consistency with the energy–momentum tensor. We prove that the use of FLRW in cosmology is valid only for zero active mass, i.e. ρ + 3 p = 0 , where ρ and p are, respectively, the total energy density and pressure in the cosmic fluid. [ABSTRACT FROM AUTHOR]

The cosmic distance duality relation (CDDR), η(z) = (1 + z)2 dA (z)/ dL (z) = 1, is one of the most fundamental and crucial formulae in cosmology. This relation couples the luminosity and angular diameter distances, two of the most often used measures of structure in the Universe. We here propose a new model-independent method to test this relation, using strong gravitational lensing (SGL) and the high-redshift quasar Hubble diagram reconstructed with a Bézier parametric fit. We carry out this test without pre-assuming a zero spatial curvature, adopting instead the value Ω K  = 0.001 ± 0.002 optimized by Planck in order to improve the reliability of our result. We parametrize the CDDR using η(z) = 1 + η0 z , 1 + η1 z + η2 z 2, and 1 + η3 z /(1 + z), and consider both the SIS and non-SIS lens models for the strong lensing. Our best-fitting results are: |$\eta _0=-0.021^{+0.068}_{-0.048}$|⁠ , |$\eta _1=-0.404^{+0.123}_{-0.090}$|⁠ , |$\eta _2=0.106^{+0.028}_{-0.034}$|⁠ , and |$\eta _3=-0.507^{+0.193}_{-0.133}$| for the SIS model, and |$\eta _0=-0.109^{+0.044}_{-0.031}$| for the non-SIS model. The measured η(z), based on the Planck parameter Ω K , is essentially consistent with the value (=1) expected if the CDDR were fully respected. For the sake of comparison, we also carry out the test for other values of Ω K , but find that deviations of spatial flatness beyond the Planck optimization are in even greater tension with the CDDR. Future measurements of SGL may improve the statistics and alter this result but, as of now, we conclude that the CDDR favours a flat Universe. [ABSTRACT FROM AUTHOR]

The geometry of the Universe may be probed using the Alcock–Paczyński (AP) effect, in which the observed redshift size of a spherical distribution of sources relative to its angular size varies according to the assumed cosmological model. Past applications of this effect have been limited, however, by a paucity of suitable sources and mitigating astrophysical factors, such as internal redshift-space distortions and poorly known source evolution. In this Letter , we introduce a new test based on the AP effect that avoids the use of spatially bound systems, relying instead on sub-samples of quasars at redshifts z  ≲ 1.5 in the Sloan Digital Sky Survey IV, with a possible extension to higher redshifts and improved precision when this catalogue is expanded by upcoming surveys. We here use this method to probe the redshift-dependent expansion rate in three pertinent Friedmann–Lemaître–Robertson–Walker cosmologies: Λ cold dark matter (ΛCDM), which predicts a transition from deceleration to acceleration at z  ∼ 0.7; Einstein–de Sitter, in which the Universe is always decelerating; and the R h = ct universe, which expands at a constant rate. ΛCDM is consistent with these data, but R h = ct is favoured overall. [ABSTRACT FROM AUTHOR]

The recent measurement of a cutoff kmin in the fluctuation power spectrum P(k) of the cosmic microwave background may vitiate the possibility that slow‐roll inflation can simultaneously solve the horizon problem and account for the formation of structure via the growth of quantum fluctuations in the inflaton field. Instead, we show that kmin may be interpreted more successfully in the Rh = ct cosmology as the first mode exiting from the Planck scale into the semiclassical universe shortly after the Big Bang. In so doing, we demonstrate that such a scenario completely avoids the well‐known trans‐Planckian problem plaguing standard inflationary cosmology. [ABSTRACT FROM AUTHOR]

Slow-roll inflation may simultaneously solve the horizon problem and generate a near scale-free fluctuation spectrum P(ĸ). These two processes are intimately connected via the initiation and duration of the inflationary phase. But a recent study based on the latest Planck release suggests that P(ĸ) has a hard cut-off, ĸmin ≠0, inconsistent with this conventional picture. Here, we demonstrate quantitatively that most--perhaps all-slow-roll inflationary models fail to accommodate this minimum cut-off. We show that the small parameter ∈ must be ... 0.9 throughout the inflationary period to comply with the data, seriously violating the slow-roll approximation. Models with such an ∈ predict extremely red spectral indices, at odds with the measured value. We also consider extensions to the basic picture (suggested by several earlier workers) by adding a kinetic-dominated or radiation-dominated phase preceding the slow-roll expansion. Our approach differs from previously published treatments principally because we require these modifications not only to fit the measured fluctuation spectrum but also simultaneously to fix the horizon problem. We show, however, that even such measures preclude a joint resolution of the horizon problem and the missing correlations at large angles. [ABSTRACT FROM AUTHOR]

Spontaneous symmetry breaking in grand unified theories is thought to have produced an exceedingly large number of magnetic monopoles in the early Universe. In the absence of suppression or annihilation, these very massive particles should be dominating the cosmic energy budget today, but none has ever been found. Inflation was invented in part to dilute their number, thereby rendering their density undetectable by current instruments. Should the inflationary paradigm not survive, however, the ensuing disagreement between theory and observation would constitute a cosmological 'monopole problem' and create further tension for any extension to the standard model of particle physics. But as is also true for all horizon problems, a monopole overabundance emerges only in cosmologies with an initial period of deceleration. We show that the alternative Friedmann–Lemaître–Robertson–Walker cosmology known as the R h = c t universe completely eliminates all such anomalies rather trivially and naturally, without the need for an inflated expansion. We find that the monopole energy density today would be completely undetectable in R h = c t. Evidence continues to grow that the zero active mass condition from general relativity ought to be an essential ingredient in Λ CDM. [ABSTRACT FROM AUTHOR]

It has been known for over three decades that the monochromatic X-ray and UV luminosities in quasars are correlated, though non-linearly. This offers the possibility of using high- z quasars as standard candles for cosmological testing. In this paper, we use a recently assembled, high-quality catalogue of 1598 quasars extending all the way to redshift ∼6, to compare the predictions of the R h = ct and Lambda cold dark matter (ΛCDM) cosmologies. In so doing, we affirm that the parameters characterizing the correlation depend only weakly on the chosen cosmology, and that both models account very well for the data. Unlike ΛCDM, however, the R h = ct model has no free parameters for this work, so the Bayesian Information Criterion favours it over ΛCDM with a relative likelihood of |$\sim 88{{\ \rm per\ cent}}$| versus |$\sim 10{{\ \rm per\ cent}}$|⁠. This result is consistent with the outcome of other comparative tests, many of which have shown that R h = ct is favoured over the standard model based on a diverse range of observations. [ABSTRACT FROM AUTHOR]

The emergence of a highly improbable coincidence in cosmological observations speaks of a remarkably simple cosmic expansion. Compelling evidence now suggests that the Universe's gravitational horizon, coincident with the better known Hubble sphere, has a radius improbably equal to the distance light could have traveled since the Big Bang. The confirmation of this unexpected result would undoubtedly herald the influence of new physics, yet appears to be unavoidable after a recent demonstration that the Friedmann–Lemaître–Robertson–Walker metric is valid only for the so-called zero active mass equation of state. As it turns out, a cosmic fluid with this property automatically produces the aforementioned equality, leaving little room for a cosmological constant. The alternative — a dynamical dark energy — would suggest an extension to the Standard Model of particle physics and a serious re-evaluation of the Universe's early history. [ABSTRACT FROM AUTHOR]

We present a phenomenological method for predicting the number of flat-spectrum radio quasars (FSRQs) that should be detected by upcoming Square Kilometre Array (SKA) SKA1-MID Wide Band 1 and Medium-Deep Band 2 surveys. We use the Fermi blazar sequence and mass estimates of Fermi FSRQs, and γ-ray emitting narrow-line Seyfert 1 galaxies, to model the radio emission of FSRQs as a function of mass alone, assuming a near-Eddington accretion rate, which is suggested by current quasar surveys at z  ≳ 6. This is used to determine the smallest visible black hole mass as a function of redshift in two competing cosmologies we compare in this paper: the standard Λ cold dark matter (ΛCDM) model and the R h =  ct universe. We then apply lockstep growth to the observed black hole mass function at z  = 6 in order to devolve that population to higher redshifts and determine the number of FSRQs detectable by the SKA surveys as a function of z. We find that at the redshifts for which this method is most valid, ΛCDM predicts ∼30 times more FSRQs than R h =  ct for the Wide survey, and ∼100 times more in the Medium-Deep survey. These stark differences will allow the SKA surveys to strongly differentiate between these two models, possibly rejecting one in comparison with the other at a high level of confidence. [ABSTRACT FROM AUTHOR]

The Universe has a gravitational horizon with a radius R h = c / H coincident with that of the Hubble sphere. This surface separates null geodesics approaching us from those receding, and as free-falling observers within the Friedmann–Lemaître–Robertson–Walker space–time, we see it retreating at proper speed c , giving rise to the eponymously named cosmological model R h = c t. As of today, this cosmology has passed over 20 observational tests, often better than Λ CDM. The gravitational radius R h therefore appears to be highly relevant to cosmological theory, and in this paper we begin to explore its impact on fundamental physics. We calculate the binding energy of a mass m within the horizon and demonstrate that it is equal to m c 2 . This energy is stored when the particle is at rest near the observer, transitioning to a purely kinetic form equal to the particle's escape energy when it approaches R h . In other words, a particle's gravitational coupling to that portion of the Universe with which it is causally connected appears to be the origin of rest-mass energy. [ABSTRACT FROM AUTHOR]

The cosmic distance duality (CDD) relation (based on the Etherington reciprocity theorem) plays a crucial role in a wide assortment of cosmological measurements. Attempts at confirming it observationally have met with mixed results, though the general consensus appears to be that the data do support its existence in nature. A common limitation with past approaches has been their reliance on a specific cosmological model, or on measurements of the luminosity distance to Type Ia SNe, which introduces a dependence on the presumed cosmology in spite of beliefs to the contrary. Confirming that the CDD is actually realized in nature is crucial because its violation would require exotic new physics. In this paper, we study the CDD using the observed angular size of compact quasar cores and a Gaussian Process reconstruction of the H ii galaxy Hubble diagram – without pre-assuming any particular background cosmology. In so doing, we confirm at a very high level of confidence that the angular-diameter and luminosity distances do indeed satisfy the CDD. We then demonstrate the potential power of this result by utilizing it in a comparative test of two competing cosmological models – the R h= ct universe and ΛCDM – and show that R h= ct is favoured by the CDD data with a likelihood |${\sim } 82.3{{\ \rm per\ cent}}$| compared with |${\sim } 17.7{{\ \rm per\ cent}}$| for the standard model. [ABSTRACT FROM AUTHOR]

Unlike other observational signatures in cosmology, the angular-diameter distance dA (z) uniquely reaches a maximum (at z max) and then shrinks to zero towards the big bang. The location of this turning point depends sensitively on the model, but has been difficult to measure. In this paper, we estimate and use z max inferred from quasar cores: (1) by employing a sample of 140 objects yielding a much reduced dispersion due to pre-constrained limits on their spectral index and luminosity, (2) by reconstructing dA (z) using Gaussian processes, and (3) comparing the predictions of seven different cosmologies and showing that the measured value of z max can effectively discriminate between them. We find that z max = 1.70 ± 0.20 – an important new probe of the Universe's geometry. The most strongly favoured model is R h = ct, followed by Planck ΛCDM. Several others, including Milne, Einstein-de Sitter, and Static tired light are strongly rejected. According to these results, the R h = ct universe, which predicts z max = 1.718, has a $${\sim } 92.8{{\ \rm per\ cent}}$$ probability of being the correct cosmology. For consistency, we also carry out model selection based on dA (z) itself. This test confirms that R h = ct and Planck ΛCDM are among the few models that account for angular-size data better than those that are disfavoured by z max. The dA (z) comparison, however, is less discerning than that with z max, due to the additional free parameter, H 0. We find that H 0 = 63.4 ± 1.2 km s−1 Mpc−1 for R h = ct, and 69.9 ± 1.5 km s−1 Mpc−1 for ΛCDM. Both are consistent with previously measured values in each model, though they differ from each other by over 4σ. In contrast, model selection based on z max is independent of H 0. [ABSTRACT FROM AUTHOR]

In general relativity, a gravitational horizon (more commonly known as the “apparent horizon”) is an imaginary surface beyond which all null geodesics recede from the observer. The Universe has an apparent (gravitational) horizon, but unlike its counterpart in the Schwarzschild and Kerr metrics, it is not static. It may eventually turn into an event horizon—an asymptotically defined membrane that forever separates causally connected events from those that are not—depending on the equation of state of the cosmic fluid. In this paper, we examine how and why an apparent (gravitational) horizon is manifested in the Friedmann–Robertson–Walker metric, and why it is becoming so pivotal to our correct interpretation of the cosmological data. We discuss its observational signature and demonstrate how it alone defines the proper size of our visible Universe. In so doing, we affirm its physical reality and its impact on cosmological models. [ABSTRACT FROM AUTHOR]

To understand the formation and evolution of galaxies at redshifts 0 ≲ z ≲ 10 , one must invariably introduce specific models (e.g., for the star formation) in order to fully interpret the data. Unfortunately, this tends to render the analysis compliant to the theory and its assumptions, so consensus is still somewhat elusive. Nonetheless, the surprisingly early appearance of massive galaxies challenges the standard model, and the halo mass function estimated from galaxy surveys at z ≳ 4 appears to be inconsistent with the predictions of Λ CDM, giving rise to what has been termed “The Impossibly Early Galaxy Problem” by some workers in the field. A simple resolution to this question may not be forthcoming. The situation with the halos themselves, however, is more straightforward and, in this paper, we use linear perturbation theory to derive the halo mass function over the redshift range 0 ≲ z ≲ 10 for the R h = c t universe. We use this predicted halo distribution to demonstrate that both its dependence on mass and its very weak dependence on redshift are compatible with the data. The difficulties with Λ CDM may eventually be overcome with refinements to the underlying theory of star formation and galaxy evolution within the halos. For now, however, we demonstrate that the unexpected early formation of structure may also simply be due to an incorrect choice of the cosmology, rather than to yet unknown astrophysical issues associated with the condensation of mass fluctuations and subsequent galaxy formation. [ABSTRACT FROM AUTHOR]

A previous analysis of starburst-dominated H ii galaxies and H ii regions has demonstrated a statistically significant preference for the Friedmann–Robertson–Walker cosmology with zero active mass, known as the Rh = ct universe, over Λcold dark matter (ΛCDM) and its related dark-matter parametrizations. In this paper, we employ a two-point diagnostic with these data to present a complementary statistical comparison of Rh = ct with Planck ΛCDM. Our two-point diagnostic compares, in a pairwise fashion, the difference between the distance modulus measured at two redshifts with that predicted by each cosmology. Our results support the conclusion drawn by a previous comparative analysis demonstrating that Rh = ct is statistically preferred over Planck ΛCDM. But we also find that the reported errors in the H ii measurements may not be purely Gaussian, perhaps due to a partial contamination by non-Gaussian systematic effects. The use of H ii galaxies and H ii regions as standard candles may be improved even further with a better handling of the systematics in these sources. [ABSTRACT FROM AUTHOR]

Measurements of the Hubble constantH(z) are increasingly being used to test the expansion rate predicted by various cosmological models. But the recent application of two-point diagnostics, such as Om(zi, zj) and Omh²(zi, zj), has produced considerable tension between CDM's predictions and several observations, with other models faring even worse. Part of this problem is attributable to the continued mixing of truly model-independent measurements using the cosmic-chronometer approach, and model-dependent data extracted from baryon acoustic oscillations. In this paper, we advance the use of two-point diagnostics beyond their current status, and introduce new variations, which we call Δh(zi, zj), that are more useful for model comparisons. But we restrict our analysis exclusively to cosmic-chronometer data, which are truly model independent. Even for these measurements, however, we confirm the conclusions drawn by earlier workers that the data have strongly non-Gaussian uncertainties, requiring the use of both 'median' and 'mean' statistical approaches. Our results reveal that previous analyses using two-point diagnostics greatly underestimated the errors, thereby misinterpreting the level of tension between theoretical predictions and H(z) data. Instead, we demonstrate that as of today, only Einstein-de Sitter is ruled out by the two-point diagnostics at a level of significance exceeding ~3σ. The Rh = ct universe is slightly favoured over the remaining models, including Lambda cold dark matter and Chevalier-Polarski-Linder, though all of them (other than Einstein-de Sitter) are consistent to within 1s with the measured mean of the Δh(zi, zj) diagnostics. [ABSTRACT FROM AUTHOR]

We use recently published redshift space distortion measurements of the cosmological growth rate, fσ8(z), to examine whether the linear evolution of perturbations in the Rh = ct cosmology is consistent with the observed development of large-scale structure. We find that these observations favour Rh = ct over the version of Λ cold dark matter (ΛCDM) optimized with the joint analysis of Planck and linear growth rate data, particularly in the redshift range 0 < z < 1, where a significant curvature in the functional form of fσ8(z) predicted by the standard model--but not by Rh = ct--is absent in the data. When ΛCDM is optimized using solely the growth rate measurements; however, the two models fit the observations equally well though, in this case, the low-redshift measurements find a lower value for the fluctuation amplitude than is expected in Planck ΛCDM. Our results strongly affirm the need for more precise measurements of fσ8(z) at all redshifts, but especially at z < 1. [ABSTRACT FROM AUTHOR]

We continue to build support for the proposal to useHII galaxies (HIIGx) and giant extragalactic HII regions (GEHR) as standard candles to construct the Hubble diagram at redshifts beyond the current reach of Type Ia supernovae. Using a sample of 25 high-redshift HIIGx, 107 local HIIGx, and 24 GEHR, we confirm that the correlation between the emission-line luminosity and ionized-gas velocity dispersion is a viable luminosity indicator, and use it to test and compare the standard model ΛCDM and the Rh = ct universe by optimizing the parameters in each cosmology using a maximization of the likelihood function. For the flat ΛCDM model, the best fit is obtained with Ωm = 0.40+0.09-0.09. However, statistical tools, such as the Akaike (AIC), Kullback (KIC) and Bayes (BIC) Information Criteria favour Rh = ct over the standard model with a likelihood of ≈94.8-98.8 per cent versus only ≈1.2-5.2 per cent. For wCDM (the version of ΛCDM with a dark-energy equation of state wde = pde/de rather than wde = wΛ =-1), a statistically acceptable fit is realized with Λm = 0.22+0.16-0.14 and wde = -0.51+0.15-0.25 which, however, are not fully consistent with their concordance values. In this case, wCDM has two more free parameters than Rh = ct, and is penalized more heavily by these criteria. We find that Rh = ct is strongly favoured over wCDM with a likelihood of ≈92.9-99.6 per cent versus only 0.4-7.1 per cent. The current HIIGx sample is already large enough for the BIC to rule out ΛCDM/wCDM in favour of Rh = ct at a confidence level approaching 3σ. [ABSTRACT FROM AUTHOR]

The extensive catalogue of gamma-ray selected flat-spectrum radio quasars (FSRQs) produced by Fermi during a four-year survey has generated considerable interest in determining their gamma-ray luminosity function (GLF) and its evolution with cosmic time. In this paper, we introduce the novel idea of using this extensive database to test the differential volume expansion rate predicted by two specific models, the concordance Λ cold dark matter (_CDM) and Rh = ct cosmologies. For this purpose, we use two well-studied formulations of the GLF, one based on pure luminosity evolution (PLE) and the other on a luminosity-dependent density evolution (LDDE). Using a Kolmogorov-Smirnov test on one-parameter cumulative distributions (in luminosity, redshift, photon index and source count), we confirm the results of earlier works showing that these data somewhat favour LDDE over PLE; we show that this is the case for both ΛCDM and Rh = ct. Regardless of which GLF one chooses, however, we also show that model selection tools very strongly favour Rh = ct over ΛCDM. We suggest that such population studies, though featuring a strong evolution in redshift, may none the less be used as a valuable independent check of other model comparisons based solely on geometric considerations. [ABSTRACT FROM AUTHOR]