Other
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006head....9.1503r&link_type=abstract
American Astronomical Society, HEAD meeting #9, #15.03; Bulletin of the American Astronomical Society, Vol. 38, p.378
Other
Scientific paper
We employ both a standard dynamical approach and a new kinematical approach to constrain cosmic acceleration using the three best available sets of redshift-independent distance measurements, from type Ia supernovae and X-ray cluster gas mass fraction measurements. The standard `dynamical' analysis employs the Friedmann equations and models dark energy as a fluid with an equation of state parameter, w. From a purely kinematical point of view, however, we can also construct models in terms of the dimensionless second and third derivatives of the scale factor a(t) with respect to cosmic time t, namely the present-day value of the deceleration parameter q_0 and the cosmic jerk parameter, j(t). A convenient feature of this parameterization is that all LambdaCDM models have j(t)=1 (constant), which facilitates simple tests for departures from the LambdaCDM paradigm. We obtain clear statistical evidence for a late time transition from a decelerating to an accelerating phase. For a flat model with constant jerk j(t)=j, we measure q_0=-0.81+-0.14 and j=2.16+0.81-0.75. For a dynamical model with constant w we measure Omega_m=0.306+0.042-0.040 and w=-1.15+0.14-0.18. Both kinematical and dynamical results are consistent with LambdaCDM at the 1sigma level. In comparison to dynamical analyses, the kinematical approach uses a different model set and employs a minimum of prior information, being independent of any particular gravity theory. We argue that both kinematical and dynamical techniques should be employed in future dark energy studies, where possible. Finally, we discuss the potential for future experiments including Constellation-X, which will constrain dark energy with comparable accuracy and in a beautifully complementary manner to the best other techniques available circa 2018.
Allen Steven W.
Amin Mustafa A.
Blandford Roger. D.
Rapetti David A.
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