Constraining dark energy from large scale structures Yipeng Jing Shanghai Astronomical Observatory
The “Hubble diagram” of Type Ia supernovae tells us that matter is not enough… log(Distance dL) a(t) Perlmutter et al. 1999, Riess et al. 1998 Redshift of spectral lines Luigi Guzzo 2
Cosmic Concordance Large-Scale Structure/Clusters m =0.25-0.3 Cosmic Microwave Background Flat geometry (TOT=1) m ~0.25 > 0 Supernovae Accelerating expansion ~ 1 Altogether (any two of them) m ~0.25 ~0.75 3
1990 Dec Nature, 348,20
Fine-tuning and Cosmic Coincidence If w=-1 and the cosmological constant corresponds to some sort of “quantum zero-point”, then its value today is a factor ~10120 too small, plus it is suspiciously fine-tuned: anthropic argument? redshift time Matter (m) Dark energy ( Today Size=2 Size=4 Size=1/2 Size=1/4 z=3 z=1 Thus could we have w = w(z) ? --> e.g. quintessence, a cosmic scalar field slowly rolling to the minimum of its potential (e.g. Wetterich 1988), inducing an evolving -1 < w(z) < -1/3. Or more complex interactions between DM and DE (e.g. Amendola 2000; Liddle et al. 2008; He et al.) ? 6
Observational Probes Supernovae M(z) Baryonic Acoustic Oscillations (BAO) Abundance of rich clusters Weak Lensing Redshift distortion
SNe Future experiments: JDEM, DES, PanSTARRS,LSST
BAO: SDSS/2dF, WiggleZ, FMOS, BOSS,Bigboss HETDEX, WFMOS, PAU Luminous Red Galaxies， LRG) two-point CF . J. Eisenstein et al., Astrophys. J. 619, 178 (2005).
But we need to look at both sides of the story… Modify gravity theory [e.g. R f(R) ] Add dark energy “…the Force be with you” 10
So, the equation of state is not the end of the story… Cosmic acceleration can also be explained by modifying the theory of gravity [as e.g. in f(R) theories, Capozziello et al. 2005, or in multi-dimensional “braneworld” models, Dvali et al. (DGP) 2000]. How to distinguish between these two options, observationally? Growth of linear density fluctuations in the expanding Universe (in GR): which has a growing solution: from which we define a growth rate The growth equation (and thus the growth rate) depends not only on the expansion history H(t) (and thus on w) but also on the gravitation theory (e.g. Lue et al. 2004) 11
Observational Probes Supernovae M(z) Baryonic Acoustic Oscillations (BAO) Abundance of rich clusters Weak Lensing Redshift distortion
Clusters:SZA, SPT, DES, ACT, 400d, eROSITA
Weak Lensing: LSST, EUCLID, DES, PanSTARRS 1.1o1.1o simulated shear field by Hamana Dq g(q) g(q+Dq)
Redshift distortion: Bigboss, Vipers, Euclid etc
张鹏杰等提出在宇宙学 尺度上检验广义相对论与其 他引力论的新方法 4个引力模型: GR，f(R)，DGP，TeVeS 张鹏杰等提出在宇宙学 尺度上检验广义相对论与其 他引力论的新方法
通过EG方法，广义相对论 在一亿光年尺度上得到了确认 Reyes et al. (Nature,464, 256-258,11 March 2010) 应用我们的EG方法分析了SDSS星系巡天的数据。 右图即为其主要结果。测量到的一亿光年尺度上的EG与广义相对论的预言相符。 该结果基本排除了TeVeS修改引力，并有力限制对f(R)引力
We also consider the dependence on the information used: the full galaxy power spectrum P(k), P(k) marginalized over its shape, or just the Baryon Acoustic Oscillations (BAO). We find that the inclusion of growth rate information (extracted using redshift space distortion and galaxy clustering amplitude measurements) leads to a factor of 3 improvement in the FoM, assuming general relativity is not modified. This inclusion partially compensates for the loss of information when only the BAO are used to give geometrical constraints, rather than using the full P(k) as a standard ruler. We
Bigboss简介 BigBOSS项目是美国劳仑斯-伯克利实验室/国家天文台发起的第四代暗能量巡天的国际合作项目（目前为第二代----第三代）；已获DOE预研经费、尚处立项阶段。 通过改造美国国家天文台的4m望远镜到直径3度的视场, 在焦面上放置5000根光纤开展光谱巡天, 光谱覆盖范围从近红外到光学，分辨率为5000；已经获准； 计划从2015年开始正式观测，在6-10年时间测量里，把暗能量状态方程的测量精度提高1-2个量级； 与其他第四代暗能量项目比较具有系统误差小、投资低、风险低的优点。
Bigboss望远镜示意图
Bigboss主要科学指标
我国参加Bigboss的作用和意义 承担光纤定位系统设计和建造关键技术； 上海台、科大等一开始参加，全面加入暗能量研究并在一些方面主导分析； 提出自己在星系形成和演化的研究方面独特的小规模巡天； 从观测能力和观测时间看，正好处在我国的LAMOST（三代，2011）和南极光学望远镜（五代，2020＋）之间 。
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