Differentiating dark energy and modified gravity with galaxy redshift surveys
- Homer L Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks Street, Norman, OK 73019 (United States)
The observed cosmic acceleration today could be due to an unknown energy component (dark energy), or a modification to general relativity (modified gravity). If dark energy models and modified gravity models are required to predict the same cosmic expansion history H(z), they will predict different growth rates for cosmic large scale structure, f{sub g}(z). If gravity is not modified, the measured H(z) leads to a unique prediction for f{sub g}(z), f{sub g}{sup H}(z), if dark energy and dark matter are separate. Comparing f{sub g}{sup H}(z) with the measured f{sub g}(z) provides a transparent and straightforward test of gravity. We show that a simple {chi}{sup 2} test provides a general figure of merit for our ability to distinguish between dark energy and modified gravity given the measured H(z) and f{sub g}(z). We find that a magnitude-limited NIR galaxy redshift survey covering >10 000 (deg){sup 2} and a redshift range of 0.5<2 can be used to measure H(z) to 1-2% accuracy via baryon acoustic oscillation measurements, and f{sub g}(z) to the accuracy of a few per cent via the measurement of redshift-space distortions and the bias factor which describes how light traces mass. We show that if the H(z) data are fitted by both a DGP gravity model and an equivalent dark energy model that predict the same H(z), a survey area of 11 931 (deg){sup 2} is required to rule out the DGP gravity model at the 99.99% confidence level. It is feasible for such a galaxy redshift survey to be carried out by the next generation space missions from NASA and ESA, and it will revolutionize our understanding of the universe by differentiating between dark energy and modified gravity.
- OSTI ID:
- 22156634
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2008, Issue 05; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
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