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Model independent expansion history from supernovae: Cosmology versus systematics
L’Huillier, Benjamin,Shafieloo, Arman,Linder, Eric V,Kim, Alex G Oxford University Press 2019 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.485 No.2
<B>Abstract</B><P>We examine the Pantheon supernovae distance data compilation in a model independent analysis to test the validity of cosmic history reconstructions beyond the concordance ΛCDM cosmology. Strong deviations are allowed by the data at z ≳ 1 in the reconstructed Hubble parameter, Om diagnostic, and dark energy equation of state. We explore three interpretations: 1) possibility of the true cosmology being far from ΛCDM, 2) supernovae property evolution, and 3) survey selection effects. The strong (and theoretically problematic) deviations at z ≳ 1 vanish and good consistency with ΛCDM is found with a simple Malmquist-like linear correction. The adjusted data is robust against the model independent iterative smoothing reconstruction. However, we caution that while by eye the original deviation from ΛCDM is striking, χ2 tests do not show the extra linear correction parameter is statistically significant, and a model-independent Gaussian Process regression does not find significant evidence for the need for correction at high-redshifts.</P>
Net Stable Funding Requirement under Basel III: Loan Portfolio Growth Matters
Barbara L’Huillier,Muhammad Suhail Rizwan,Dawood Ashraf 한국증권학회 2018 Asia-Pacific Journal of Financial Studies Vol.47 No.4
This paper evaluates the perceived stability-enhancing role of the net stable funding ratio (NSFR) requirement under Basel III and its impact on the balance sheets of banks. Using data from 647 banks located in 47 countries from 2003 to 2013, we find that the NSFR would have played a financial stability-enhancing role if it had been implemented during the sample period. However, the NSFR requirement would also have had a loan portfolio shrinkage affect and increases the possibility of sub-optimal loan portfolio selection. Our results suggest that there are costs and benefits to implementing the NSFR requirement.
HORIZON RUN 4 SIMULATION: COUPLED EVOLUTION OF GALAXIES AND LARGE-SCALE STRUCTURES OF THE UNIVERSE
KIM, JUHAN,PARK, CHANGBOM,L'HUILLIER, BENJAMIN,HONG, SUNGWOOK E. The Korean Astronomical Society 2015 Journal of The Korean Astronomical Society Vol.48 No.4
The Horizon Run 4 is a cosmological N-body simulation designed for the study of coupled evolution between galaxies and large-scale structures of the Universe, and for the test of galaxy formation models. Using 6300<sup>3</sup> gravitating particles in a cubic box of L<sub>box</sub> = 3150 h<sup>−1</sup>Mpc, we build a dense forest of halo merger trees to trace the halo merger history with a halo mass resolution scale down to M<sub>s</sub> = 2.7 × 10<sup>11</sup>h<sup>−1</sup>M<sub>⊙</sub>. We build a set of particle and halo data, which can serve as testbeds for comparison of cosmological models and gravitational theories with observations. We find that the FoF halo mass function shows a substantial deviation from the universal form with tangible redshift evolution of amplitude and shape. At higher redshifts, the amplitude of the mass function is lower, and the functional form is shifted toward larger values of ln(1/σ). We also find that the baryonic acoustic oscillation feature in the two-point correlation function of mock galaxies becomes broader with a peak position moving to smaller scales and the peak amplitude decreasing for increasing directional cosine μ compared to the linear predictions. From the halo merger trees built from halo data at 75 redshifts, we measure the half-mass epoch of halos and find that less massive halos tend to reach half of their current mass at higher redshifts. Simulation outputs including snapshot data, past lightcone space data, and halo merger data are available at <uri>http://sdss.kias.re.kr/astro/Horizon-Run4</uri>.
Model-independent cosmological constraints from growth and expansion
L'Huillier, Benjamin,Shafieloo, Arman,Kim, Hyungjin Oxford University Press 2018 Monthly notices of the Royal Astronomical Society Vol.476 No.3
<P>Reconstructing the expansion history of the Universe from Type Ia supernovae data, we fit the growth rate measurements and put model-independent constraints on some key cosmological parameters, namely, Omega(m), gamma, and sigma(8). The constraints are consistent with those from the concordance model within the framework of general relativity, but the current quality of the data is not sufficient to rule out modified gravity models. Adding the condition that dark energy density should be positive at all redshifts, independently of its equation of state, further constrains the parameters and interestingly supports the concordance model.</P>