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Melia, Fulvio (21)

Univ Arizona, Dept Astron (21)

Melia, Fulvio (16)Univ Arizona, Dept Phys, Appl Math Program (14)Univ Arizona, Dept Phys (7)Univ Arizona, Dept Phys, Program Appl Math (6)Melia, Fulvio (5)Leaf, Kyle (4)Leaf, Kyle (4)Yennapureddy, Manoj K. (3)View MoreTypes
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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.

Analysing H(z) data using two-point diagnostics

Leaf, Kyle; Melia, Fulvio (OXFORD UNIV PRESS, 2017-09)

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 Omh(2)(zi, zj), has produced considerable tension between Lambda 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 Delta h(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 similar to 3s. The R-h = 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 1 sigma with the measured mean of the Delta h(zi, zj) diagnostics.

A two-point diagnostic for the H ii galaxy Hubble diagram

Leaf, Kyle; Melia, Fulvio (OXFORD UNIV PRESS, 2017-12-01)

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 cold dark matter (CDM) 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 CDM.
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 CDM. 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.

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.

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.

Model selection based on the angular-diameter distance to the compact structure in radio quasars

Melia, Fulvio (IOP PUBLISHING LTD, 2018-09-03)

Of all the distance arid temporal measures in cosmology, the angular-diameter distance, d(A)(z), uniquely reaches a maximum value at some finite redshift z(max )and then decreases to zero towards the Big Bang. This effect has been difficult to observe due to a lack of reliable, standard rulers, though refinements to the identification of the compact structure in radio quasars may have overcome this deficiency. In this letter, we assemble a catalog of 140 such sources with 0 less than or similar to z less than or similar to 3 for model selection and the measurement of z(max). In flat Lambda CDM, we find that Omega(m) = 0.24(-0.09)(+0.1) fully consistent with the Planck optimized value, with z(max) = 1.69. Both of these values are associated with a d(A)(z) indistinguishable from that predicted by the zero active mass condition, rho + 3p = 0, in terms of the total pressure rho and total energy density rho of the cosmic fluid. An expansion driven by this constraint, known as the Rh = ct universe, has z(max )= 1.718, which differs from the Lambda CDM optimized value by less than similar to 1.6%. Indeed, the Bayes Information Criterion favours R-h = ct over flat Lambda CDM with a likelihood of similar to 81% vs. 19%, suggesting that the optimized parameters in Planck Lambda CDM mimic the constraint p = -rho/3.

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.

A cosmological basis for E = mc2

Melia, Fulvio (WORLD SCIENTIFIC PUBL CO PTE LTD, 2019-04-10)

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-Lemaitre-Robertson-Walker space-time, we see it retreating at proper speed c, giving rise to the eponymously named cosmological model R-h = ct. As of today, this cosmology has passed over 20 observational tests, often better than Lambda 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 mc(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.

The linear growth of structure in the Rh = ct universe

Melia, Fulvio (OXFORD UNIV PRESS, 2017-01-11)

We use recently published redshift space distortion measurements of the cosmological growth rate, f sigma(8)(z), to examine whether the linear evolution of perturbations in the R-h = ct cosmology is consistent with the observed development of large-scale structure. We find that these observations favour R-h = ct over the version of Lambda cold dark matter (Lambda CDM) 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 f sigma(8)(z) predicted by the standard model-but not by R-h = ct-is absent in the data. When Lambda CDM 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 Lambda CDM. Our results strongly affirm the need for more precise measurements of f sigma(8)(z) at all redshifts, but especially at z < 1.

Evidence of a truncated spectrum in the angular correlation function of the cosmic microwave background

Melia, Fulvio; López-Corredoira, M. (EDP SCIENCES S A, 2018-03-09)

Aim. The lack of large-angle correlations in the fluctuations of the cosmic microwave background (CMB) conflicts with predictions of slow-roll inflation. But while probabilities (≲0.24%) for the missing correlations disfavour the conventional picture at ≳3σ, factors not associated with the model itself may be contributing to the tension. Here we aim to show that the absence of large-angle correlations is best explained with the introduction of a non-zero minimum wave number kmin for the fluctuation power spectrum P(k).
Methods. We assumed that quantum fluctuations were generated in the early Universe with a well-defined power spectrum P(k), although with a cut-off kmin ≠ 0. We then re-calculated the angular correlation function of the CMB and compared it with Planck observations.
Results. The Planck 2013 data rule out a zero kmin at a confidence level exceeding 8σ. Whereas purely slow-roll inflation would have stretched all fluctuations beyond the horizon, producing a P(k) with kmin = 0 – and therefore strong correlations at all angles – a kmin ≠ 0 would signal the presence of a maximum wavelength at the time (tdec) of decoupling. This argues against the basic inflationary paradigm, and perhaps even suggests non-inflationary alternatives, for the origin and growth of perturbations in the early Universe. In at least one competing cosmology, the Rh = ct universe, the inferred kmin corresponds to the gravitational radius at tdec.

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