Dark Energy

1. Dark Energy L The first Surprise in the era of precision cosmology? Q

2. L Dark Energy Evidence Low redshift cosmic geometry Q

3. L Dark Energy Evidence Large Scale Structure Galaxy distribution favours a low matter Universe; CMB acoustic peak locations indicate a flat cosmic geometry Evidence for 70 % of the critical energy density in the vacuum Q Percival et al. MNRAS 327 1297 2001

4. L Vacuum Energy: a Mystery For Physics The Planck mass is 1019 GeV; a natural scale for the vacuum energy density would be Particle physics takes the Standar Model form at the mass scale of the electroweak vector bosons: L» 1076 GeV4 L» 108 GeV4 Q Instead, present observations indicate a vacuum energy density comparable to the critical one: ? ? ? ? L» 10-49 h2GeV4 ?

5. ?? L for Physics Two ? Why L so small with respect to any particle physics scale ? Why comparable to the cosmological matter density today Q

6. L Dark Energy Models • Trans Planckian: energy stored in perturbation modes on super-horizon scales (Mersini et al., PRD64 043508, 2001) • Spacetime microstructure: self-adjusting spacetime capable to absorbe vacuum energy (Padmanabhan, gr-qc/0204020) • Matter-Energy Transition: dark matter converts to dark energy at low redshifts (astro-ph/0203383) • Brane worlds: brane tension (Shani & Sthanov astro-ph/0202346); cyclic-ekpyrotic cosmic vacuum (Steinhardt &Tutok hep-th/0111098) • Quintessence: tracking scalar fields (Steinhardt, Wang & Zlatev, • PRD59, 123504, 1999; Ratra & Peebles, Wetterich ...) • Extended Quintessence: non-minimal coupling to Gravity (Uzan • Chiba, Perrotta, Baccigalupi, Matarrese, PRD61, 023507, 2000 • Coupled Quintessence: coupling with dark matter (Amendola, • Pietroni...) Q

7. L Quintessence The Quintessence scalar field f slowly rolls down its potential V(f), becoming dominant at low redshift, flat enough to mimick the behavior of a Cosmological Constant. Q

8. L Quintessence Cosmilogy Background Evolution: Perturbation Evolution: Q (synchronous gauge)

9. L Quintessence Tracking Solutions For interesting forms of potentials, attractor trajectories have the following property: Inverse power law potential: Q

10. L Why are Tracking Solutions Important? Avoid Fine-Tuning in the Early Universe! Q

11. L Unlike the Cosmological Constant... Quintessence fluctuates! Q (Newtonian gauge)

12. Dark Energy L CMB constraints & Extended Theory Q

13. L Effects on the CMB • Projection • Integrated Sachs-Wolfe Q

14. L Effects on the CMB Projection: ISW (Bardeen 1980): Q

15. L Quintessence & CMB Advantages: well understood geometrical features of high amplitude, well above the sensitivity of MAP & Planck Q Disdvantages: CMB degeneracy (Efstathiou 2001); in particular, the projecttion is degenerate with a positive spatial curvature

16. L Quintessence & CMB: simulations Hubble constant fixed, no spatial curvature: h=0.65,WK=0 Cosmological abundances: 0.016·Wb· 0.04 (step 0.02), 0.4·Wf· 0.8, step 0.02, WCDM=1-Wf-Wb Quintessence equation of state: -0.96· wf· –0.6 (step 0.03), wf=-1 Q Cosmological Perturbations: 0.90· ns· 1.10 (step 0.02), 0· R· 0.5 (step 0.05), nT=-R/6/8 Gaussian, adiabatic initial conditions

17. Quintessence & CMB: data L BOOMERanG: 19 points, 76· l· 1025 MAXIMA: 13 points, 36· l· 1235 DASI: 13 points, 36· l· 1235 COBE: 24 points, 2· l· 25 Q Gaussian likelihood assumed, calibration uncertainty included

18. L Quintessence & CMB: early results Balbi et al. 2001 Q

19. L Quintessence & CMB: results Baccigalupi et al. 2002 Q

20. Quintessence & CMB: wf ,Wf L Baccigalupi et al. 2002 Q

21. L Quintessence & CMB: results Q

22. L Is there a projection on the CMB? L CDM vs. QCDM Q

23. L Quintessence & CMB: conslusions In flat cosmologies, h fixed, CMB data show a mild preference for a time varying dark energy: 0.6·Wf· 0.8, -1· wf· –0.6 (2s ) Wf=0.71-0.04+0.05, wf=-0.82-0.11+0.14 (1s ) Q

24. L Extended Quintessence in analogy with Extended Inflation models Formulate Quintessence theory in Generalized General Relativity: Presently explored classes: RQ with

25. L Why non-minimal coupling? • The theory has to be extended, the simplest model does not work • Extend the theory to the Gravitational sector • Can Dark Energy be the signature of a modification of General Relativity? RQ

26. L Extended Cosmic Expansion RQ

27. L Scalar-Tensor Cosmological Perturbations h, h: metric trace & traceless perturbation RQ dr, dp: total density & pressure perturbation q, s: total velocity & shear perturbation

28. Varying G encoded in fluid propertes (Hwang 1991) Perrotta et al. 2000

29. L Tracking Extended Quintessence Extended Quintessence admits tracking solutions The early time behavior differs from ordinary GR because of R; at early times: R-boost RQ

30. L Tracking Extended Quintessence: R-boost shrinks to RQ

31. L Tracking Extended Quintessence: R-boost for the R-boost solution is RQ

32. L Tracking Extended Quintessence: R-boost The R-boost ends when the energy density equals the potential RQ

33. L Changing Gravity Changing CMB RQ Baccigalupi et al. 2000

34. L Extended Quintessence & CMB: ISW * for x <0 + for x >0 RQ if F=1/8p G +xf2 , d Cl/Cl' 96p Gxf02

35. L Extended Quintessence & CMB: Projection RQ if F=1/8p G +xf2 , dl/l'p Gxf02

36. L Gravitational Dragging RQ

37. L Gravitational Dragging: Background rf scales as the dominant component RQ

38. Gravitational Dragging: Perturbations L Dark energy sound speed (Hu 1998): In the matter dominated era: RQ

39. Dark Energy Clustering L Redshift behavior of dk2=4p k3(dr /r)k2 Perrotta & Baccigalupi 2002 RQ

40. L Extended Quintessence: Conclusions Extended Quintessence admits tracking solutions The Ricci scalar causes an initial enhancement of the field dynamics, the R-boost Projection: dl/l' (1-G/Gdec)/8 ISW: d Cl/Cl' 12(1-G/Gdec) Gravitational Dragging: the dark energy density scales as the dominant component Q Gravitational Dragging: dark energy density perturbations track the matter ones ) it participates to structure formation (!)

41. L Dark Energy Evidence Q