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A comparison of the R_h = ct and LCDM cosmologies based on the observed halo mass function

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arXiv 2019年

作者： Yennapureddy, Manoj K. Melia, Fulvio Department of Physics University of Arizona TucsonAZ85721 United States Applied Math Program Department of Physics University of Arizona TucsonAZ85721 United States

The growth of structure probes the re-ionization history and quasar abundance in the Universe, constituting an important probe of the cosmological predictions. Halos are not directly observable, however, so their mass and evolution must be inferred indirectly. Studies based on the assumption of a constant halo to stellar mass ratio M_h/M_∗ (extrapolated from z Copyright © 2019, The Authors. All rights reserved.

关键词： Galaxies

Test of the cosmic distance duality relation for arbitrary spatial curvature

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arXiv 2021年

作者： Qin, Jin Melia, Fulvio Zhang, Tong-Jie Department of Astronomy Beijing Normal University Beijing100875 China Department of Physics The Applied Math Program Department of Astronomy The University of Arizona AZ85721 United States

The cosmic distance duality relation (CDDR), η(z) = (1 + z)2dA(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 ΩK = 0.001 ± 0.002 optimized by Planck in order to improve the reliability of our result. We parametrize the CDDR using η(z) = 1+η0z, 1+η1z+η2z2 and 1+η3z/(1+z), and consider both the SIS and non-SIS lens models for the strong lensing. Our best fit results are: η0 = −0.021+0.068-0.048, η1 = −0.404+0.123-0.090, η2 = 0.106+0.028-0.034, and η3 = −0.507+0.193-0.133 for the SIS model, and η0 = −0.109+0.044-0.031 for the non-SIS model. The measured η(z), based on the Planck parameter ΩK, 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 ΩK, 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. Copyright © 2021, The Authors. All rights reserved.

关键词： Cosmology

The maximum angular-diameter distance in cosmology

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arXiv 2018年

作者： Melia, Fulvio Yennapureddy, Manoj K. Department of Physics Applied Math Program Department of Astronomy University of Arizona AZ85721 United States Department of Physics University of Arizona AZ85721 United States

Unlike other observational signatures in cosmology, the angular-diameter distance dA(z) uniquely reaches a maximum (at zmax) 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 zmaxinferred 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 zmaxcan effectively discriminate between them. We find that zmax= 1.70 ± 0.20- an important new probe of the Universe's geometry. The most strongly favoured model is Rh = ct, followed by Planck λCDM. Several others, including Milne, Einstein-de Sitter and Static tired light are strongly rejected. According to these results, the Rh = ct universe, which predicts zmax= 1.718, has a ~ 92.8% probability of being the correct cosmology. For consistency, we also carry out model selection based on dA(z) itself. This test confirms that Rh = ct and Planck λCDM are among the few models that account for angular-size data better than those that are disfavoured by zmax. The dA(z) comparison, however, is less discerning than that with zmax, due to the additional free parameter, *** find that H0 = 63.4±1.2 km s-1Mpc-1for Rh = ct, and 69.9 ± 1.5 km s-1Mpc-1for 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 zmaxis independent of H0. Copyright © 2018, The Authors. All rights reserved.

关键词： Galaxies

Structure formation and the matter power-spectrum in the Rh = ct universe

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arXiv 2020年

作者： Yennapureddy, Manoj Kumar Melia, Fulvio Department of Physics University of Arizona AZ85721 United States Department of Physics Applied Math Program Department of Astronomy University of Arizona AZ85721 United States

Inflation drives quantum fluctuations beyond the Hubble horizon, freezing them out before the small-scale modes re-enter during the radiation dominated epoch, and subsequently decay, while large-scale modes re-enter later during the matter dominated epoch and grow. This distinction shapes the matter power spectrum and provides observational evidence in support of the standard model. In this paper, we demonstrate that another mechanism, based on the fluctuation growth in the Rh = ct universe, itself an FLRW cosmology with the added constraint of zero active mass (i.e., ρ + 3p = 0), also accounts very well for the observed matter power spectrum, so this feature is not unique to ΛCDM. In Rh = ct, the shape of the matter power spectrum is set by the interplay between the more rapid decay of the gravitational potential for the smaller mode wavelengths and the longer dynamical timescale for the larger wavelengths. This combination produces a characteristic peak that grows in both amplitude and mode number as a function of time. Today, that peak lies at k ≈ 0.02 Mpc−1, in agreement with the Ly-α and Planck data. But there is no need of an inflationary expansion, and a complicated epoch dependence as one finds in ΛCDM. © 2020, CC-BY.

关键词： Gravitation

Assessing cosmic acceleration with the Alcock-Paczyński effect in the SDSS-IV quasar catalog

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arXiv 2020年

作者： Melia, Fulvio Qin, Jin Zhang, Tong-Jie Department of Physics The Applied Math Program Department of Astronomy The University of Arizona AZ85721 United States Department of Astronomy Beijing Normal University Beijing100875 China

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 catalog is expanded by upcoming surveys. We here use this method to probe the redshift-dependent expansion rate in three pertinent Friedmann-Lemaître-Robertson-Walker (FLRW) cosmologies: 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 Rh = ct universe, which expands at a constant rate. ΛCDM is consistent with these data, but Rh = ct is favoured overall. Copyright © 2020, The Authors. All rights reserved.

关键词： Galaxies

The Cosmic Timeline Implied by the JWST Reionization Crisis

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arXiv 2024年

作者： Melia, Fulvio Department of Physics The Applied Math Program The University of Arizona TucsonAZ85721 United States Department of Astronomy The University of Arizona TucsonAZ85721 United States

Context. JWST’s discovery of well-formed galaxies and supermassive black holes only a few hundred Myr after the big bang, and the identification of polycyclic aromatic hydrocarbons (PAHs) at z = 6.71, seriously challenge the timeline predicted by ΛCDM. Moreover, the implied bright UV-irradiation of the early Universe suggests a reionization history much too short to comply with the observed evolution of the hydrogen ionization fraction, xHII(z). Aims. A recent analysis of reionization after JWST by Muñoz et al. (2024) has concluded that the ΛCDM timeline simply cannot accommodate the combined JWST-Planck observations even if exotic fixes are introduced to modify the standard reionization model. In this paper, we argue that this so-called ‘photon budget crisis’ is more likely due to flaws in the cosmological model itself. We aim to re-analyze the data in the context of established astrophysics with Rh = ct as the background cosmology, an approach that has already been shown to mitigate the tension created by the too-early appearance of galaxies, quasars and PAHs. Methods. We employ the standard reionization model using the JWST-measured UV luminosity function in the early Universe and the timeline and physical conditions in both ΛCDM and Rh = ct. The former has already been fully probed and discussed by Muñoz et al. (2024), and we here merely redo the calculation to ensure consistency with their pioneering work. We then contrast the predicted reionization histories in these two scenarios and compare them with the data. Results. We confirm that the reionization history predicted by ΛCDM is in significant tension with the observations, and demonstrate that the latter are instead in excellent agreement with the Rh = ct timeline. Conclusions. Together, the four anomalies uncovered by JWST, including the newly discovered reionization ‘crisis’ discussed in this paper, provide strong evidence against the timeline predicted by ΛCDM and in favor of the evolutionary history in

关键词： Polycyclic aromatic hydrocarbons

Challenges to Inflation in the Post-Planck Era

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arXiv 2024年

Space-based missions studying the cosmic microwave background (CMB) have progressively refined the parameter space in conventional models of inflation shortly (∼ 10−37 seconds) after the big bang. While most inflationary scenarios proposed thus far in the context of GR have since been ruled out, the basic idea of inflation may still be tenable, albeit with several unresolved conundrums, such as conflicting initial conditions and inconsistencies with the measured CMB power spectrum. In the new slow-roll inflationary picture, inflation arising in plateau-like potentials requires an initiation beyond the Planck time. This delay may be consistent with the cutoff, kmin, measured recently in the primordial power spectrum. However, the actual value of kmin would imply an initiation time too far beyond the big bang for inflation to solve the horizon problem. In this paper, we also describe several other undesirable consequences of this delay, including an absence of well motivated initial conditions and a significant difficulty providing a viable mechanism for properly quantizing the primordial fluctuations. Nevertheless, many of these inconsistencies may still be avoided if one introduces non-conventional modifications to inflation, such as a brief departure from slow-roll dynamics, possibly due to a dramatic change in the inflationary potential, inflation driven by multiple fields, or a non-minimal coupling to gravity. In addition, some of these difficulties could be mitigated via the use of alternative cosmologies based, e.g., on loop quantum gravity, which replaces the initial big-bang singularity with finite conditions at a bounce-like beginning. Copyright © 2024, The Authors. All rights reserved.

关键词： Power spectrum

Analyzing H(z) data using two-point diagnostics

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arXiv 2017年

作者： Leaf, Kyle Melia, Fulvio Department of Physics University of Arizona AZ85721 United States Department of Physics Applied Math Program Department of Astronomy University of Arizona AZ85721 United States

Measurements of the Hubble constant H(z) are increasingly being used to test the expansion rate predicted by various cosmologicalmodels. But the recent application of 2-point diagnostics, such as Om(zi, zj) and Omh2(zi, zj), has produced considerable tension between ΛCDM's predictions and several observations, with other models faring even worse. Part of this problem is attributable to the continued mixing of truly model-independentmeasurements using the cosmic-chronomter approach, and model-dependent data extracted from BAOs. In this paper, we advance the use of 2-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 2-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 2-point diagnostics at a level of significance exceeding ∼ 3σ. The Rh= ct universe is slightly favoured over the remaining models, including ΛCDM and Chevalier- Polarski-Linder, though all of them (other than Einstein-de Sitter) are consistent to within 1σ with the measured mean of the Δh(zi, zj) diagnostics. Copyright © 2017, The Authors. All rights reserved.

关键词： Chronometers

Viability of slow-roll inflation in light of the non-zero kmin measured in the CMB power spectrum

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arXiv 2020年

Slow-roll inflation may simultaneously solve the horizon problem and generate a near scale-free fluctuation spectrum P (k). 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 (k) has a hard cutoff, kmin 6= 0, inconsistent with this conventional picture. Here we demonstrate quantitatively that most'perhaps all'slow-roll inflationary models fail to accommodate this minimum cutoff. We show that the small parameter ǫ must be & 0.9 throughout the inflationary period to comply with the data, seriously violating the slow-roll approximation. Models with such an ǫ 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 to'not only fit the measured fluctuation spectrum, but to simultaneously also'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. Copyright © 2020, The Authors. All rights reserved.

关键词： Power spectrum