1. 1 L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina Open page http://leandros.physics.uoi.gr/uoi06.htm

2. 2 Accellerating Expansion of the Universe from SNe Ia (and other) datasets Accelerating Expansion: Dark Energy or Modified Gravity The Gravitational Properties of Dark Energy are getting severely constrained by Cosmological Observations Extended Gravity Theories can be observationally distinguished from Dark Energy

3. 3 FRW Metric Two Parameters: Geometry ( Curvature k=-1,0,+1), Scale (Scale Factor a(t)) Closed Flat Open Universe Expands

4. 4 Directly Observable Dark Energy (Inferred) No Yes Flat Friedmann Equation

5. 5 Accelerating Universe: (rate of expansion) was smaller in the past. Thus H -1 (t) was larger in the past.

6. 6

7. 7 SnIa Obs

8. 8 2 12 Know L Measure l(z) Distance Modulus: 1 Flat

9. 9 Gold Dataset (157 SNeIa): Riess et. al. 2004 Decelerating Accelerating ?

10. 10 z~0.5: Acceleration starts

11. 11 Expected: Decelerated Expansion due to Gravity Observed: Accelerated Expansion Q: What causes the Acceleration?

12. 12 1.Observed: Accelerated Expansion Expected: Deceleration due to Gravity Q: What causes acceleration? 2.Observed (CMB): Flat Geometry (ρ tot =ρ crit ) (LSS) : ρ 0m =0.3ρ crit Expected: ρ 0m =ρ crit Q: Where (and what) is the missing mass? 3.Observed: Globular Cluster Age=13Gyrs Expected (ρ 0m =ρ crit ): Age 13Gyrs)?

13. 13 Induces Repulsive Gravity (Accelerates) Has positive energy density (missing mass) Can increase the age of the Universe

14. 14 Equation of State: Necessary condition for acceleration:

15. 15 a(t) t t0t0 PRESENT tHtH 0 2t H /3 t0t0 t H =H 0 -1 empty univ accelerating universe k =  No D.E. decelerating universe k =  +D.E. k =  1, No D.E.

16. 16 (from large scale structure observations)

17. 17 Einstein (1915) G.R.: Einstein (1917) G.R. + Static Universe + Matter only: G  =  T  G  -  g  =  T  The biggest blunder of my life

18. 18 Since I introduced this term, I had always a bad conscience.... I am unable to believe that such an ugly thing is actually realized in nature A. Einstein 1947 letter to Lemaitre

19. 19 Beauty: Flat Matter DominatedUgly: Cosmological Constant

20. 20  Positive pressure pushes against the piston Negative pressure pulls in the piston (spring force)   Constant energy per unit volume  V > 0   U=ρ Λ ΔV> 0 Energy conservation:  U= –p Λ  V (  V > 0,  U > 0)  (p Λ < 0) constant  energy conservation  negative p F ΔVΔV

21. 21 Flat

22. 22 SNLS Truncated Gold Full Gold S. Nesseris, L.P. astro-ph/0511040 Phys.Rev.D72:123519,2005 Gold Dataset (157 SNeIa): Riess et. al. 2004 SNLS (115 SNeIa): Astier et. al. 2005

23. 23

24. 24

25. 25 S. Nesseris, L.P. astro-ph/0511040 Phys.Rev.D72:123519,2005

26. 26 +: Quintessence -: Phantom To cross the w=-1 line the kinetic energy term must change sign (impossible for single phantom or quintessence field) Generalization for k-essence:

27. 27 Non-minimal Coupling

28. 28

29. 29 Minimum: Generic feature F(Φ) ΦΦ U(Φ) L.P. astro-ph/0504582, JCAP 0510:001,2005, S. Nesseris, L.P. astro-ph/0502053, 2006 (accepted in Phys. Rev. D) JCAP 0511:010,2005

30. 30 The Expansion of the Universe is currently accelerating. This acceleration can be modeled either by a Dark Energy or by Extended Gravity Theories. All recent SnIa data indicate that w(z) is close to -1. Thus w(z) may be crossing the w=-1 line. Minimally Coupled Scalar predicts no crossing of w=-1 line Scalar Tensor Theories are consistent with crossing of w=-1

31. 31 Radial Geodesics: S. Nesseris, L. P., Phys.Rev.D70:123529,2004

32. 32 S. Nesseris, L. P., Phys.Rev.D70:123529,2004

33. 33 S. Nesseris, L. P., Phys.Rev.D70:123529,2004

34. 34 Gold+CMB+BAO Gold+CMB+BAO+Clusters+SNLS Gold Gold+CMB+BAO+Clusters Crossing of w=-1 consistent with all datasets! S. Nesseris, L.P. in preparation Obs Luminosity Distance Ang. Diameter Distance Standard Ruler: Sound Horizon (z=z rec,z=0.35) d A (z) from Clusters w z

35. 35

36. 36

37. 37 ESSENCE CFHT Legacy Survey Higher-z SN Search (GOODS) SN Factory Carnegie SN Project SNAP

38. 38 1. Measurements of the Cosmological Parameters Omega and Lambda from the First 7 Supernovae at z >= 0.35 S. Perlmutter et al., Astrophys.J. 483 (1997) 565 2. Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant S. Perlmutter et al., Nature 391 (1998) 51 3. Discovery of Supernova Explosion at Half the Age of the Universe A.G. Riess et al., Astron.J. 116 (1998) 1009-1038

39. 39 4. Cosmological results from high-z supernovae Tonry et al. The Astrophysical Journal, 594:1-24, 2003 September 1 5. New Constraints on Ω M, Ω Λ, and w from an Independent Set of 11 High-Redshift Supernovae Observed with the Hubble Space Telescope R.A. Knop et al., The Astrophysical Journal, Volume 598, Issue 1, pp. 102-137 Decelerating Expansion starts at z=0.46 11 new SnIa observed from HST 6. Type Ia Supernova Discoveries at z > 1 From the Hubble Space Telescope: Evidence for Past Deceleration and Constraints on Dark Energy Evolution A. Riess et al. The Astrophysical 607:665-687,2004 16 new SnIa observed from HST 7 of them with z>1.25

40. 40 2m Telescope ~1 billion pixels, 144 CCDs 350-1700 nm wavelength coverage Finds and follows 2500 SnIa each year, out to z = 1.7 Place good limits on both w and its time evolution