New Kinematical Constraints on Cosmic Acceleration

Computer Science

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Scientific paper

We present and employ a new kinematical approach to 'dark energy' studies. We 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 q0 and the cosmic jerk parameter, j(t). An elegant feature of this parameterization is that all ΛCDM models have j(t) = 1 (constant), which facilitates simple tests for departures from the ΛCDM paradigm. Applying our model to redshift-independent distance measurements, from type Ia supernovae and X-ray cluster gas mass fraction measurements, 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 q0 = -0.8l ± 0.14 and j = 2.16{ - 0.75}{ + 0.81} , results that are consistent with ΛCDM at about the 1σ confidence 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. The results obtained with this new approach therefore provide important additional information and we argue that both kinematical and dynamical techniques should be employed in future dark energy studies, where possible.

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