Probing the curvature and dark energy

1. Probing the curvature and dark energy Gong, Yungui 龚云贵 Chongqing University of Posts and Telecommunications 重庆邮电学院 2005 International Summer School/Institute on Particle Physics, Astrophysics and Cosmology (Section II)，August 16, 2005

2. Dark Energy Introduction • Introduction to SN Fitting Method • Current Status of Parameterizations • One-parameter Parameterization • Comments • Conclusion

3. Why Dark Energy? Riess etal. astro-ph/0402512

4. Introduction to SN Fitting Method Assume flat universe and Robertson-Walker metric

5. The SNe Ia data in Riess etal. lists the distance moduliμ0, Using the least square fit, we can reconstruct the function H(z) in general. In standard model, we know

6. Marginalization Since appears linearly in the form of in , so the marginalization by integrating over all possible values of is equivalent to finding the value of which minimizes if we also include the suitable integration constant and measure function,

7. Parameterizations • Taylor expansion of Hubble parameter, M. Visser, CQG 21 (2004) 2603 • Prameterizations of energy density: 2nd Order Polynomial, U. Alam etal. MNRAS 354 (2004) 275 • Negative Power Polynomial, U. Alam etal. MNRAS 354 (2004) 275

8. Common Parameterization of WQ • Constant equation of state w • Linear equation of state w=w0+w1z • Stable Parameterizations • Wetterich Parameterization • Parameterization H.K. Jassal, MNRAS 356(2005) L11

9. Fitting Results Y. Gong, astro-ph/0405446 , Class. Quantum Grav. 22 (2005) 2121 • Taylor expansion of Hubble parameter

16. Supernova Fit to dark energy

17. One parameter Parameterization Y. Gong and Y.Z. Zhang, astro-ph/0502262, PRD in press

22. Results

23. Summary

25. Comments • What can we say about acceleration? • (Starkman, Trodden and Vachaspati)

27. Dark Energy with constant EOS

30. Y. Gong and Y.Z. Zhang, gr-qc/0508053

33. Conclusion

34. Thanks!