Bright High z SnIa: A Challenge for LCDM?

Abstract

It has recently been pointed out by Kowalski et. al. (arxiv:0804.4142) that there is `an unexpected brightness of the SnIa data at z>1'. We quantify this statement by constructing a new statistic which is applicable directly on the Type Ia Supernova (SnIa) distance moduli. This statistic is designed to pick up systematic brightness trends of SnIa datapoints with respect to a best fit cosmological model at high redshifts. It is based on binning the normalized differences between the SnIa distance moduli and the corresponding best fit values in the context of a specific cosmological model (eg LCDM). We then focus on the highest redshift bin and extend its size towards lower redshifts until the Binned Normalized Difference (BND) changes sign (crosses 0) at a redshift z_c (bin size N_c). The bin size N_c of this crossing (the statistical variable) is then compared with the corresponding crossing bin size N_{mc} for Monte Carlo data realizations based on the best fit model. We find that the crossing bin size N_c obtained from the Union08 and Gold06 data with respect to the best fit LCDM model is anomalously large compared to N_{mc} of the corresponding Monte Carlo datasets obtained from the best fit LCDM in each case. In particular, only 2.2% of the Monte Carlo LCDM datasets are consistent with the Gold06 value of N_c while the corresponding probability for the Union08 value of N_c is 5.3%. Thus, according to this statistic, the probability that the high redshift brightness bias of the Union08 and Gold06 datasets is realized in the context of a (w_0,w_1)=(-1,0) model (LCDM cosmology) is less than 6%. The corresponding realization probability in the context of a (w_0,w_1)=(-1.4,2) model is more than 30% for both the Union08 and the Gold06 datasets.

8 pages, 7 figures. Extended analysis, added two figures, results unchanged. The data and the mathematica v.5.2 files used for the production of the figures may be downloaded from http://leandros.physics.uoi.gr/bnd.zip. Accepted in Physical Review D (to appear)

References in corpus (34)

• Dynamics of dark energy
• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Improved Cosmological Constraints from New, Old and Combined Supernova Datasets
• Observational Constraints on the Nature of the Dark Energy: First Cosmological Results from the ESSENCE Supernova Survey
• Measuring the Baryon Acoustic Oscillation scale using the SDSS and 2dFGRS
• Two new diagnostics of dark energy
• Very weak lensing in the CFHTLS Wide: Cosmology from cosmic shear in the linear regime
• Measuring the dark side (with weak lensing)
• Large Scale Structure as a Probe of Gravitational Slip
• Distinguishing Modified Gravity from Dark Energy
• Cosmology with Weak Lensing Surveys
• Consequences of dark matter-dark energy interaction on cosmological parameters derived from SNIa data
• Testing LCDM with the Growth Function δ(a): Current Constraints
• The acceleration of the universe and the physics behind it
• On the growth of linear perturbations
• Comparison of Cluster Lensing Profiles with Lambda CDM Predictions
• Crossing of the phantom divide in modified gravity
• Discovery of a tight correlation among the prompt emission properties of long Gamma Ray Bursts
• The growth of matter perturbations in f(R) models
• Differentiating dark energy and modified gravity with galaxy redshift surveys
• Model Independent Reconstruction of the Expansion History of the Universe and the Properties of Dark Energy
• Next Generation Redshift Surveys and the Origin of Cosmic Acceleration
• Growth factor parametrization and modified gravity
• Late acceleration and $w=-1$ crossing in induced gravity
• Growth Index of DGP Model and Current Growth Rate Data
• Comparison of Standard Ruler and Standard Candle constraints on Dark Energy Models
• Parameterizing the Effect of Dark Energy Perturbations on the Growth of Structures
• Accelerating cosmologies tested by distance measures
• The LambdaCDM model on the lead -- a Bayesian cosmological models comparison
• Bayesian Evidence for a Cosmological Constant using new High-Redshift Supernovae Data
• Non-parametric Dark Energy Degeneracies
• Reconstructing the properties of dark energy from recent observations
• Probing the cosmic acceleration history and the properties of dark energy from the ESSENCE supernova data with a model independent method
• Why we need to see the dark matter to understand the dark energy

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• Backreaction: directions of progress
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• A model independent null test on the cosmological constant
• Slow-roll k-essence
• Constraining dark energy with gamma-ray bursts
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• Comparison of Recent SnIa datasets
• The Crossing Statistic: Dealing with Unknown Errors in the Dispersion of Type Ia Supernovae
• A magnified glance into the dark sector: probing cosmological models with strong lensing in A1689
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• Unparticle dark energy
• Tension between SN and BAO: current status and future forecasts
• Study of the observational compatibility of an inhomogeneous cosmology with linear expansion according to SNe Ia
• Parametrization for the Scale Dependent Growth in Modified Gravity
• Inflection Point Quintessence
• Testing Local Anisotropy Using the Method of Smoothed Residuals I - Methodology
• Falsifying Cosmological Constant
• Remarks on (super-)accelerating cosmological models in general scalar-tensor gravity
• Genetic algorithms and the analysis of SnIa data
• The Quadratic Approximation for Quintessence with Arbitrary Initial Conditions
• Coincidence Problem in Cyclic Phantom Models of the Universe