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JournalMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY (4)AMERICAN JOURNAL OF PHYSICS (2)ASTRONOMY & ASTROPHYSICS (2)EUROPEAN PHYSICAL JOURNAL C (2)PHYSICS OF THE DARK UNIVERSE (1)The Astrophysical Journal (1)Authors

Melia, Fulvio (12)

Univ Arizona, Dept Astron (12)

Univ Arizona, Dept Phys, Appl Math Program (10)Univ Arizona, Dept Phys (4)Leaf, Kyle (2)Univ Arizona, Dept Phys, Program Appl Math (2)Yennapureddy, Manoj K. (2)Ruan, Cheng-Zong (1)Yennapureddy, Manoj K. (1)Zhang, Tong-Jie (1)TypesArticle (12)
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Cosmological tests with strong gravitational lenses using Gaussian processes

Yennapureddy, Manoj K.; Melia, Fulvio (SPRINGER, 2018-03-24)

Strong gravitational lenses provide source/lens distance ratios D-obs useful in cosmological tests. Previously, a catalog of 69 such systems was used in a one-on-one comparison between the standard model, Lambda CDM, and the R-h = ct universe, which has thus far been favored by the application of model selection tools to many other kinds of data. But in that work, the use of model parametric fits to the observations could not easily distinguish between these two cosmologies, in part due to the limited measurement precision. Here, we instead use recently developed methods based on Gaussian Processes (GP), in which D-obs may be reconstructed directly from the data without assuming any parametric form. This approach not only smooths out the reconstructed function representing the data, but also reduces the size of the 1 sigma confidence regions, thereby providing greater power to discern between different models. With the current sample size, we show that analyzing strong lenses with a GP approach can definitely improve the model comparisons, producing probability differences in the range similar to 10-30%. These results are still marginal, however, given the relatively small sample. Nonetheless, we conclude that the probability of R-h = ct being the correct cosmology is somewhat higher than that of Lambda CDM, with a degree of significance that grows with the number of sources in the subsamples we consider. Future surveys will significantly grow the catalog of strong lenses and will therefore benefit considerably from the GP method we describe here. In addition, we point out that if the R-h = ct universe is eventually shown to be the correct cosmology, the lack of free parameters in the study of strong lenses should provide a remarkably powerful tool for uncovering the mass structure in lensing galaxies.

The apparent (gravitational) horizon in cosmology

Melia, Fulvio (AMER ASSOC PHYSICS TEACHERS, 2018-08)

In general relativity, a gravitational horizon (more commonly known as the "apparent horizon") 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. (C) 2018 American Association of Physics Teachers.

J1342+0928 supports the timeline in the R-h = ct cosmology

Melia, Fulvio (EDP SCIENCES S A, 2018-07-24)

Aims. The discovery of quasar J1342+0928 (z = 7.54) reinforces the time compression problem associated with the premature formation of structure in A cold dark matter (ACDM). Adopting the Planck parameters, we see this quasar barely 690 Myr after the big bang, no more than several hundred Myr after the transition from Pop III to Pop II star formation. Yet conventional astrophysics would tell us that a 10 M-circle dot seed, created by a Pop II/III supernova, should have taken at least 820 Myr to grow via Eddington-limited accretion. This failure by ACDM constitutes one of its most serious challenges, requiring exotic "fixes", such as anomalously high accretion rates, or the creation of enormously massive (similar to 10(5) M-circle dot) seeds, neither of which is ever seen in the local Universe, or anywhere else for that matter. Indeed, to emphasize this point, J1342+0928 is seen to be accreting at about the Eddington rate, negating any attempt at explaining its unusually high mass due to such exotic means. In this paper, we aim to demonstrate that the discovery of this quasar instead strongly confirms the cosmological timeline predicted by the R-h = Ct Universe. Methods. We assume conventional Eddington-limited accretion and the time versus redshift relation in this model to calculate when a seed needed to start growing as a function of its mass in order to reach the observed mass of J1342+0928 at z = 7.54. Results. Contrary to the tension created in the standard model by the appearance of this massive quasar so early in its history, we find that in the R-h = Ct cosmology, a 10 M-circle dot seed at z similar to 15 (the start of the Epoch of Reionization at t similar to 878 Myr) would have easily grown into an 8 x 10(8) M-circle dot black hole at z = 7.54 (t similar to 1.65 Gyr) via conventional Eddington-limited accretion.

A comparison of the R_h=ct and LCDM cosmologies using the Cosmic Distance Duality Relation

Melia, Fulvio (OXFORD UNIV PRESS, 2018-09-21)

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 Rh = ct universe and ΛCDM – and show that Rh = ct is favoured by the CDD data with a likelihood ∼82.3 per cent compared with ∼17.7 per cent for the standard model.

Model-independent Test of the Cosmic Distance Duality Relation

Ruan, Cheng-Zong; Melia, Fulvio; Zhang, Tong-Jie (IOP PUBLISHING LTD, 2018-10-08)

A validation of the cosmic distance duality (CDD) relation, h() ( ) () () z zdz dz º+ = 1 A L 1 2 , coupling the
luminosity (dL) and angular-diameter (dA) distances, is crucial because its violation would require exotic new
physics. We present a model-independent test of the CDD, based on strong lensing and a reconstruction of the H II
galaxy Hubble diagram using Gaussian processes, to confirm the validity of the CDD at a very high level
of confidence. Using parameterizations h( )z z = +1 h0 and h( )z zz =+ + 1 h h 1 2
2, our best-fit results are
h = -
+ 0.0147 0 0.066
0.056, and h = -
+ 0.1091 1 0.1568
0.1680 and h = - -
+ 0.0603 2 0.0988
0.0999, respectively. In spite of these strong
constraints, however, we also point out that the analysis of strong lensing using a simplified single isothermal
sphere (SIS) model for the lens produces some irreducible scatter in the inferred CDD data. The use of an extended
SIS approximation, with a power-law density structure, yields very similar results, but does not lessen the scatter
due to its larger number of free parameters, which weakens the best-fit constraints. Future work with these strong
lenses should therefore be based on more detailed ray-tracing calculations to determine the mass distribution more
precisely

Model selection with strong-lensing systems

Leaf, Kyle; Melia, Fulvio (OXFORD UNIV PRESS, 2018-05-24)

In this paper, we use an unprecedentedly large sample (158) of confirmed strong lens systems for model selection, comparing five well-studied Friedmann–Robertson–Walker cosmologies: ΛCDM, wCDM (the standard model with a variable dark-energy equation of state), the Rh = ct universe, the (empty) Milne cosmology, and the classical Einstein-de Sitter (matter-dominated) universe. We first use these sources to optimize the parameters in the standard model and show that they are consistent with Planck, though the quality of the best fit is not satisfactory. We demonstrate that this is likely due to underreported errors, or to errors yet to be included in this kind of analysis. We suggest that the missing dispersion may be due to scatter about a pure single isothermal sphere (SIS) model that is often assumed for the mass distribution in these lenses. We then use the Bayes information criterion, with the inclusion of a suggested SIS dispersion, to calculate the relative likelihoods and ranking of these models, showing that Milne and Einstein-de Sitter are completely ruled out, while Rh = ct is preferred over ΛCDM/wCDM with a relative probability of ∼73percent versus ∼24percent. The recently reported sample of new strong lens candidates by the Dark Energy Survey, if confirmed, may be able to demonstrate which of these two models is favoured over the other at a level exceeding 3σ.

A cosmological solution to the Impossibly Early Galaxy Problem

Yennapureddy, Manoj K.; Melia, Fulvio (ELSEVIER SCIENCE BV, 2018-03-26)

To understand the formation and evolution of galaxies at redshifts 0 less than or similar to z less than or similar to 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 some-what elusive. Nonetheless, the surprisingly early appearance of massive galaxies challenges the standard model, and the halo mass function estimated from galaxy surveys at z greater than or similar to 4 appears to be inconsistent with the predictions of Lambda 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 less than or similar to z less than or similar to 10 for the R-h = ct 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 Lambda 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.

J1342+0928 supports the timeline in the = cosmology

A solution to the electroweak horizon problem in the $$R_\mathrm{h}=ct$$Rh=ct universe

Melia, Fulvio (SPRINGER, 2018-09)

Particle physics suggests that the Universe may have undergone several phase transitions, including the well- known inflationary event associated with the separation of the strong and electroweak forces in grand unified theories. The accelerated cosmic expansion during this transition, at cosmic time t ∼ 10−36 − 10−33 s, is often viewed as an explanation for the uniformity of the CMB temperature, T , which would otherwise have required inexplicable initial conditions. With the discovery of the Higgs particle, it is now quite likely that the Universe underwent another (elec- troweak) phase transition, at T = 159.5 ± 1.5 GeV – roughly ∼ 10−11 s after the big bang. During this event, the fermions gained mass and the electric force separated from the weak force. There is currently no established explanation, however, for the apparent uniformity of the vacuum expectation value of the Higgs field which, like the uniformity in T , gives rise to its own horizon problem in standard ΛCDM cosmology. We show in this paper that a solution to the electroweak horizon problem may be found in the choice of cosmological model, and demonstrate that this issue does not exist in the alterna- tive Friedmann–Robertson–Walker cosmology known as the Rh = ct universe.

The maximum angular-diameter distance in cosmology

Melia, Fulvio; Yennapureddy, Manoj K. (OXFORD UNIV PRESS, 2018-07-23)

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 zmax 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 zmax can 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 PlanckΛCDM. 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 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 Rh = ct and PlanckΛCDM 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, H0. We find that H0 = 63.4 ± 1.2 km s−1 Mpc−1 for Rh = 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 zmax is independent of H0.

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