Dark Energy – a cosmic mystery

1. Dark Energy – a cosmic mystery

2. Quintessence C.Wetterich A.Hebecker, M.Doran, M.Lilley, J.Schwindt, C.Müller, G.Schäfer, E.Thommes, R.Caldwell, M.Bartelmann, K.Kharwan, G.Robbers, T.Dent, S.Steffen, L.Amendola, M.Baldi , N.Brouzakis , N.Tetradis, D.Mota, V.Pettorino, T.Krüger, M.Neubert

3. What is our universe made of ? fire , air, water, soil ! quintessence !

4. Dark Energy dominates the Universe Energy - density in the Universe = Matter + Dark Energy 25 % + 75 %

5. What is Dark Energy ?

6. Composition of the universe Ωb = 0.045 Ωdm= 0.225 Ωh = 0.73

7. critical density • ρc =3 H² M² critical energy density of the universe ( M : reduced Planck-mass , H : Hubble parameter ) • Ωb=ρb/ρc fraction in baryons energy density in baryons over critical energy density

8. Baryons/Atoms Dust Ωb=0.045 Only 5 percent of our Universe consist of known matter ! SDSS ~60,000 of >300,000 Galaxies

9. Abell 2255 Cluster ~300 Mpc

11. Ωb=0.045 from nucleosynthesis, cosmic background radiation

12. Matter : Everything that clumps Abell 2255 Cluster ~300 Mpc

13. Dark Matter Ωm = 0.25 total “matter” Most matter is dark ! So far tested only through gravity Every local mass concentration gravitational potential Orbits and velocities of stars and galaxies measurement of gravitational potential and therefore of local matter distribution

14. Ωm= 0.25 gravitational lens , HST

15. Gravitationslinse,HST

16. Gravitationslinse,HST

17. Matter : Everything that clumps Ωm= 0.25 Abell 2255 Cluster ~300 Mpc

18. spatially flat universe Ωtot = 1 • theory (inflationary universe ) Ωtot =1.0000……….x • observation ( WMAP ) Ωtot =1.02 (0.02)

19. picture of the big bang

21. Mean values WMAP 2003 Ωtot =1.02 Ωm =0.27 Ωb =0.045 Ωdm =0.225

22. Ωtot=1

23. Ωtot=1

24. WMAP 2006 Polarization

25. Dark Energy Ωm + X = 1 Ωm : 25% Ωh : 75% Dark Energy h : homogenous , often ΩΛ instead of Ωh

26. Space between clumps is not empty :Dark Energy !

27. Dark Energy density isthe same at every point of space “ homogeneous “ No force in absence of matter –“ In what direction should it draw ? “

28. Predictions for dark energy cosmologies The expansion of the Universe accelerates today !

29. Structure formation : One primordial fluctuation spectrum CMB agrees with Galaxy distribution Lyman – α and Gravitational Lensing ! Waerbeke

30. Power spectrum Baryon - Peak galaxy – correlation – function M.Tegmark + … Structure formation : One primordial fluctuation- spectrum SDSS

31. consistent cosmological model !

32. Composition of the Universe Ωb = 0.045 visible clumping Ωdm= 0.2 invisibleclumping Ωh = 0.75 invisiblehomogeneous

33. Dark Energy – a cosmic mystery

34. What is Dark Energy ? Cosmological Constant or Quintessence ?

35. Cosmological Constant- Einstein - • Constant λ compatible with all symmetries • No time variation in contribution to energy density • Why so small ? λ/M4 = 10-120 • Why important just today ?

36. Cosm. Const. | Quintessence static | dynamical

37. Energy density ρ ~ ( 2.4×10 -3 eV )- 4 Reduced Planck mass M=2.44×10 27 eV Newton’s constant GN=(8πM²) Cosmological mass scales Only ratios of mass scales are observable ! homogeneous dark energy: ρh/M4 = 6.5 10ˉ¹²¹ matter: ρm/M4= 3.5 10ˉ¹²¹

38. Time evolution tˉ² matter dominated universe tˉ3/2 radiation dominated universe • ρm/M4 ~ aˉ³ ~ • ρr/M4 ~ aˉ4~ t -2radiation dominated universe Huge age small ratio Same explanation for small dark energy?

39. Quintessence Dynamical dark energy , generated by scalarfield (cosmon) C.Wetterich,Nucl.Phys.B302(1988)668, 24.9.87 P.J.E.Peebles,B.Ratra,ApJ.Lett.325(1988)L17, 20.10.87

40. Prediction : homogeneous dark energyinfluences recent cosmology- of same order as dark matter - Original models do not fit the present observations …. modifications

41. Quintessence Cosmon – Field φ(x,y,z,t) similar to electric field , but no direction ( scalar field ) Homogeneous und isotropic Universe : φ(x,y,z,t)=φ(t) Potential und kinetic energy of the cosmon -field contribute to a dynamical energy density of the Universe !

42. Cosmon • Scalar field changes its value even in the presentcosmological epoch • Potential und kinetic energy of cosmon contribute to the energy density of the Universe • Time - variable dark energy : ρh(t) decreases with time !

43. Evolution of cosmon field Field equations Potential V(φ) determines details of the model V(φ) =M4 exp( - αφ/M ) for increasing φ the potential decreases towards zero !

44. Cosmon • Tiny mass • mc ~ H (depends on time ! ) • New long - range interaction

45. “Fundamental” Interactions Strong, electromagnetic, weak interactions On astronomical length scales: graviton + cosmon gravitation cosmodynamics

46. observation will decide !

47. Time dependence of dark energy cosmological constant : Ωh ~ t² ~ (1+z)-3 M.Doran,…

48. Cosmic Attractors Solutions independent of initial conditions typically V~t -2 φ ~ ln ( t ) Ωh ~ const. details depend on V(φ) or kinetic term early cosmology

49. exponential potentialconstant fraction in dark energy can explain order of magnitude of dark energy ! Ωh = 3/α2

50. effects of early dark energy • modifies cosmological evolution (CMB) • slows down the growth of structure