paper

Comparison of Standard Ruler and Standard Candle constraints on Dark Energy Models

arXiv:0712.1232 · doi:10.1088/1475-7516/2008/07/012

Abstract

We compare the dark energy model constraints obtained by using recent standard ruler data (Baryon Acoustic Oscillations (BAO) at z=0.2 and z=0.35 and Cosmic Microwave Background (CMB) shift parameters R and l_a) with the corresponding constraints obtained by using recent Type Ia Supernovae (SnIa) standard candle data (ESSENCE+SNLS+HST from Davis et. al.). We find that, even though both classes of data are consistent with LCDM at the 2σlevel, there is a systematic difference between the two classes of data. In particular, we find that for practically all values of the parameters (Ω_0m,Ω_b) in the 2σrange of the the 3-year WMAP data (WMAP3) best fit, LCDM is significantly more consistent with the SnIa data than with the CMB+BAO data. For example for (Ω_0m,Ω_b)=(0.24,0.042) corresponding to the best fit values of WMAP3, the dark energy equation of state parametrization w(z)=w_0 + w_1 (z/(1+z)) best fit is at a 0.5σdistance from LCDM (w_0=-1,w_1=0) using the SnIa data and 1.7σaway from LCDM using the CMB+BAO data. There is a similar trend in the earlier data (SNLS vs CMB+BAO at z=0.35). This trend is such that the standard ruler CMB+BAO data show a mild preference for crossing of the phantom divide line w=-1, while the recent SnIa data favor LCDM. Despite of this mild difference in trends, we find no statistically significant evidence for violation of the cosmic distance duality relation η\equiv d_L(z)/(d_A(z) (1+z)^2)=1. For example, using a prior of Ω_0m=0.24, we find η=0.95 \pm 0.025 in the redshift range 0<z<2, which is consistent with distance duality at the 2σlevel.

arXiv commentReferences added. 9 pages, 7 figures. The Mathematica files with the numerical analysis of the paper can be found at http://leandros.physics.uoi.gr/rulcand/rulcand.htm

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