用星系红移巡天区分暗能量和修正引力
Differentiating dark energy and modified gravity with galaxy redshift surveys
摘要：
今天观测到的宇宙加速可能是由于一种未知的能量成分（暗能量），或者是对广义相对论的修正（修正的引力）。如果要求暗能量模型和修正的引力模型预测相同的宇宙膨胀历史H（z），它们将预测不同的宇宙大尺度结构增长率，f_g（z）= \ln δ/\ln a（δ=（ρ_m- \bar{ρ_m}）/ \bar{ρ_m}），a为宇宙尺度因子）。如果重力不被修改，测量的H（z）导致f_g（z）的唯一预测，f_g^H（z）。将f_g^H（z）与测量的f_g（z）进行比较，可以提供一个透明而直接的重力测试。我们表明，在给定测量的H（z）和f_g（z）的情况下，简单的χ^2检验为我们区分暗能量和修正引力的能力提供了一般品质因数。我们研究了一个星等受限的近红外星系红移巡天，覆盖范围> 10，000（deg）^2，红移范围为0.5<z<2。所得数据可分为7个红移面元，通过重子声学振荡测量得到H（z）的精度为1-2%，通过测量红移空间畸变和描述光跟踪质量的偏置因子得到f_g（z）的精度为百分之几。我们发现，如果H（z）数据同时用DGP引力模型和等价的暗能量模型拟合，并且预测了相同的膨胀历史，那么需要11，931（deg）^2的调查区域才能在99.99%的置信水平上排除DGP引力模型。由美国航天局和欧空局的下一代空间任务进行这样的星系红移调查是可行的，它将通过区分暗能量和修正引力来彻底改变我们对宇宙的理解。
英文摘要：
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 rate for cosmic large scale structure, f_g(z)=d\ln δ/d\ln a (δ=(ρ_m-\bar{ρ_m})/\bar{ρ_m}), a is the cosmic scale factor). If gravity is not modified, the measured H(z) leads to a unique prediction for f_g(z), f_g^H(z). Comparing f_g^H(z) with the measured f_g(z) provides a transparent and straightforward test of gravity. We show that a simple χ^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_g(z). We study a magnitude-limited NIR galaxy redshift survey covering >10,000 (deg)^2 and the redshift range of 0.5<z<2. The resultant data can be divided into 7 redshift bins, and yield the measurement of H(z) to the accuracy of 1-2% via baryon acoustic oscillation measurements, and f_g(z) to the accuracy of a few percent via the measurement of redshift space distortions and the bias factor which describes how light traces mass. We find that if the H(z) data are fit by both a DGP gravity model and an equivalent dark energy model that predict the same expansion history, a survey area of 11,931 (deg)^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.
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