1. Recent Progress on Dark Energy Study Xinmin Zhang IHEP2007-09-07

2. Outline Global analysis on the determination of cosmological parameters Global analysis on the determination of cosmological parameters 1) The dynamics of Inflation? 2) The dynamical dark energy? Quintom Bounce Quintom Bounce Interacting dark energy Interacting dark energy cosmological CPT violation and CMB polarization

3. Inflation Predictions: 1. Flat Universe ( ); 2. and, Current Status: 1., fit well; 2. about ; 3. about.

4. Curvature of Universe J.Q.Xia et al. arXiv:0708.1111

5. Inflationary Models J.Q.Xia et al. arXiv:0708.1111

6. Constraint on the inflationary models Large-field Inflation Hybrid Inflation Small-field Inflation Implication for Inflation Models?

7. Dark Energy Classification of the Dark Energy Models: 1. ; 2. ;. Current Status: 1. fits well; 2., less than

8. Equation of State of Dark Energy

9. WMAP3+LSS+SN WMAP3+LSS+SN+GRB Hong Li, M. su, Z.H. Fan, Z.G. Dai and X.Zhang, astro-ph/0612060

10. The study with GRBs: E.L.Wright astro-ph/0701584

11. Existence (√) Existence (√) Nature (?) Nature (?) Modified Gravity, DGP Model (disfavored) Modified Gravity, DGP Model (disfavored) (Consistent check? Comments) (Consistent check? Comments) W(z): Cosmological constant; Quintessence; Phantom; Quintom; …… W(z): Cosmological constant; Quintessence; Phantom; Quintom; …… If dynamical, interaction … If dynamical, interaction … Variation of fine structure coupling constant; Variation of fine structure coupling constant; Cosmological P and CPT violation; Cosmological P and CPT violation; Mass varying Neutrino; Mass varying Neutrino; Effects on the determinations of cosmological parameters Effects on the determinations of cosmological parameters Observations ( Data and range of redshift ) limited; Observations ( Data and range of redshift ) limited; Interestingly and important: study the implications of dark energy in the evolution of universe ( bounce, fate of universe ) ---- dynamical model

16. I. Dynamics of Inflation and Dark Energy: Weak! II. Surprising: 1. too large; 2. crossing : theoretical challenge. III. Inflation: Dynamical (generally believing) Dark Energy: Dynamical ? My personal View: Dynamical Dark Energy Fate of the Universe somehow connected to “ Pre Big-Bang ” Quintom Bounce!! Important Chinese contribution!!

17. No-Go Theorem For theory of dark energy (DE) in the 4D Friedmann- Robertson-Walker (FRW) universe described by a single perfect fluid or a single scalar field with a lagrangian of, which minimally couples to Einstein Gravity, its equation of state w cannot cross over the cosmological constant boundary. Bo Feng et al., Phys. Lett. B 607, 35 (2005); A. Vikman, Phys. Rev. D 71, 023515 (2005); W. Hu, Phys. Rev. D 71, 047301 (2005); R. R. Caldwell and M. Doran, Phys. Rev. D 72, 043527 (2005); Gong-Bo Zhao et al., Phys. Rev. D 72, 123515 (2005); H. Wei, PhD Thesis (2006); M. Kunz and D. Sapone, Phys. Rev. D 74, 123503 (2006); …… J. Xia, Y. F. Cai, T. Qiu, G. B. Zhao and X. M. Zhang, astro-ph/0703202

18. Double Field Model Bo Feng, Xiulian Wang and Xinmin Zhang, Phys. Lett. B 607, 35 (2005) Action: Potential:  Classical: w can cross -1 easily  If quantized: un- stable because of ghost!

19. Single Scalar Field with High Derivative Action:  Classical: w can also cross -1 due to HD operator.  Quantum: avoid in- stability if taking c-term perturbatively.

20. String-inspired Quintom Model Action ： Different from conventional single scalar field with high derivative, this Quintom model (beta term involves two scalars and two derivatives, the same as alpha term) has its HD term residing in the square root. This model can be viewed as a generalization of tachyon models. Potential: Yifu Cai et al., Phys. Lett. B 651, 1 (2007), [arXiv: hep-th/0701016]

21. The dilemma of Big Bang Cosmology Though widely recognized, there are still problems existing in Big Bang Cosmology: Though widely recognized, there are still problems existing in Big Bang Cosmology: Singularity Problem Singularity Problem Flatness Problem Flatness Problem Homogeneity Problem Homogeneity Problem Large Scale Structure Large Scale Structure Unwanted Relics Unwanted Relics 。。。。。。 。。。。。。 Inflationary Cosmology can solve most of these problems, but singularity still remains a problem. Inflationary Cosmology can solve most of these problems, but singularity still remains a problem.

22. Basic idea of Quintom Bounce The expanding of the universe is transited from a contracting phase; during the transition the scale factor of the universe is at its minimum but non-vanishing, thus the singularity problem can be avoided. Contracting phase ： Expanding Phase: At the boun- cing point: Around it: Transition to the observable universe (radiation dominant, matter dominant,…) So w needs to cross -1, and Quintom is required ！ Yifu Cai et al., arXiv:0704.1090 [gr-qc]

23. A phenomenological Quintom model with the equation of state across -1 can lead to a bouncing solution. I. Quintom Bounce with Parameterized EoS

24. II. Quintom Bounce with Double Fields The action ： where

25. III. Quintom Bounce with a single scalar field The action: where

26. Imprints of bouncing on CMB? Y. S. Piao, B. Feng and X. M. Zhang, Phys. Rev. D 69, 103520 (2004) A scenario, a contracting phase followed by an inflationary phase, can provide a reasonable explanation for lower CMB anisotropies on large angular scales. Released WMAP data show a low value of quadrupole in the CMB temperature fluctuations.

27. WMAP1 WMAP3 Low CMB Quadrupole & Wiggles WMAP1 WMAP3

28. Interacting dark energy Coupling to Baryon, Cold dark matter Coupling to Baryon, Cold dark matter constraints from …… constraints from …… Coupling to Neutrinos: Mass varying Neutrino Coupling to Neutrinos: Mass varying Neutrino Interaction with derivatives Interaction with derivatives cosmological CPT violation cosmological CPT violation Baryo-/Leptogenesis Baryo-/Leptogenesis CMB polarization CMB polarization

29. M.Li et al. PRD65:103511,2002 PLB573:20,2003 H.Li et al. PRD70:047302,2004

30. Quintessential Baryo/Leptogenesis M.Li, X.Wang, B.Feng, X. Zhang PRD65,103511 (2002) M.Li & X. Zhang ， PLB573,20 (2003) The value of depends on the model of Quintessence Cosmological CPT violation! In thermo equilibrium Cohen & Kaplan

31. 模型检验 : Bo Feng, Hong Li, Minzhe Li and Xinmin Zhang Phys. Lett. B620(2005)27 其中 : 有效理论： 由 baryogenesis: 实验探测 : in the future CMB polarization experiments will be Tested.

32. Searching for CPT violation

33. Cosmological CPT violation: Predicting and Bo Feng, Mingzhe Li, Jun-Qing Xia, Xuelei Chen and Xinmin Zhang Phys. Rev. Lett. 96, 221302 (2006) (Note here the notation: G ~ E, C~ B)

34. Our preliminary result: WMAP3+BOOMERANG -6.2+/-3.8 deg Compare with old result: -5.9+/-3.9 deg

35. Summary Inflation? PLANCK Inflation? PLANCK Dark Energy? SNAP Dark Energy? SNAPLAMOST?! Probing for fundamental physics (string theory) Probing for fundamental physics (string theory) Precision measurement of CMB accurate test on CPT ……

36. Thank you !