• Model selection with strong-lensing systems

  Leaf, Kyle; Melia, Fulvio; Univ Arizona, Dept Phys; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (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.
• The apparent (gravitational) horizon in cosmology

  Melia, Fulvio; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (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.
• Evidence of a truncated spectrum in the angular correlation function of the cosmic microwave background

  Melia, F.; López-Corredoira, M.; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (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.
• Model selection based on the angular-diameter distance to the compact structure in radio quasars

  Melia, F.; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (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.
• Green Infrastructure and its Applications on the University of Arizona Campus

  Bulik, Claire; College of Architecture, Planning and Landscape Architecture; McCormick, Grant; Iuliano, Joey (The University of Arizona., 2018-12)

  Cities all around the world are experiencing new challenges in the wake of climate change. In the United States the effects of climate change, coupled with failing infrastructure, are leading to major problems when it comes to flooding and storm water management. With the predicted increase and severity of storm events due to climate change, storm water mitigation is becoming an important task for planners, engineers, and landscape architects. Green infrastructure is emerging as a solution to these challenges where in place of traditional infrastructure multi-layered systems that mimic natural processes are being used to capture, treat and infiltrate storm water on site. This capstone examines the various components of green infrastructure design and how it can be utilized on the University of Arizona campus. This research, in addition to quantitative storm water calculations, have been used to inform the re-design of a site on campus using green infrastructure practices to mitigate flooding and capture storm water runoff. Through a carefully planned green infrastructure approach, the proposed design captures 90% of the storm water that falls in a 100-year, 60-minute design storm on site.

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