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Dark Energy

Dark Energy. L. The first Surprise in the era of precision cosmology?. Q. L. Dark Energy Evidence. Low redshift cosmic geometry. Q. L. Dark Energy Evidence. Large Scale Structure. Galaxy distribution favours a low matter Universe; CMB acoustic peak locations indicate a

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Dark Energy

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  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

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