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L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina

Open page. Repulsive Gravity and the Accelerating Universe. http://leandros.physics.uoi.gr/uoi06.htm. L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina. Main Points of Talk.

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L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina

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  1. Open page Repulsive Gravity and the Accelerating Universe http://leandros.physics.uoi.gr/uoi06.htm L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina

  2. Main Points of Talk • 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 constrainedby Cosmological Observations • Extended Gravity Theories can be observationally distinguishedfrom Dark Energy

  3. Universe Description Homogeneous-Isotropic System + Perturbations General Relativity Two Parameters: Geometry ( Curvature k=-1,0,+1), Scale (Scale Factor a(t)) Universe Expands FRW Metric Closed Open Flat Flat: Favored by Observations and Theory

  4. Dynamics: The Dark Energy Puzzle Friedmann Equation Flat General Relativity DirectlyObservable Dark Energy(Inferred) DirectlyObservable Q: Is GR the correct theory on the Largest Scales? What is the Correct Theory? No Yes What are the properties of the dark energy? What microphysical theory can reproduce these properties?

  5. Hubble Diagram Accelerating Universe: (rate of expansion) was smaller in the past. Thus H-1(t) was larger in the past. Standard Candles SNeIa Luminus Objects of a given redshift appear to be further away (dimmer) in an Accelerating Universe

  6. SnIa Physics White Dwarf Accretion from Companion Cross Chandrasekhar Limit Ignite Carbon Fusion Explode

  7. Obs SnIa Expansion History from Luminosity Distance Absolute luminocity L: Total Power Radiated Apparent luminocity l: Luminocity Distance: Physical Distance in Static Universe Expanding Universe: comoving distance

  8. Expansion History from Luminosity Distance Expanding Universe: 1 Flat Light Geodesics 2 1 2 Know L Measure l(z) Distance Modulus:

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

  10. Observed Hubble Diagram z~0.5: Acceleration starts

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

  12. Cosmological Puzzles ? • Observed: Accelerated ExpansionExpected: Deceleration due to GravityQ: What causes acceleration? • Observed (CMB): Flat Geometry (ρtot=ρcrit)(LSS) : ρ0m=0.3ρcritExpected: ρ0m=ρcritQ: Where (and what) is the missing mass? • Observed: Globular Cluster Age=13GyrsExpected (ρ0m=ρcrit): Age < (2/3)H0-1=10GyrsQ: Why is the universe so old (t0>13Gyrs)?

  13. Resolution of the three Puzzles Dark Energy with Negative Pressure • Induces Repulsive Gravity (Accelerates) • Has positive energy density (missing mass) • Can increase the age of the Universe Concordance Model

  14. Negative Pressure Acceleration from Dynamics of scale factor a(t): Friedman eqn General Relativity Homogeneity-Isotropy Equation of State: Necessary condition for acceleration: Dark Energy Antigravity

  15. Acceleration Solves the Cosmic Age Problem k =0+D.E. a(t) empty univ accelerating universe k =0, No D.E. decelerating universe PRESENT k = +1, No D.E. t0 0 t 2tH/3 tH tH=H0-1 t0

  16. Evolution Dark Energy Energy Conservation: Friedman Equation Best Fit ? (from large scale structure observations)

  17. the cosmological constant w=-1 Gmn = k Tmn • Einstein (1915) G.R.: • Einstein (1917) G.R. + Static Universe + Matter only: Gmn- L gmn = k Tmn Cosmic Repulsion Cosmological Constant Then came: Hubble's Discovery (1929) • The biggest blunder of my life Einstein :

  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. Beauty: Flat Matter Dominated Ugly: Cosmological Constant Cosmological Data

  20. Cosmological Constant: Physical Meaning ΔV L F Constant energy per unit volumeDV > 0  DU=ρΛ ΔV> 0 Energy conservation:DU= –pΛDV (DV > 0, DU > 0)  (pΛ < 0) constant r + energy conservation negative p • Positive pressure pushes against the piston Negative pressurepulls in the piston (spring force)

  21. Fitting the Cosmological Constant Friedman Equation Flat Theory Observations -Observations Theory- Compare:

  22. Comparative analysis for LCDM SNLS (115 SNeIa): Astier et. al. 2005 Gold Dataset (157 SNeIa): Riess et. al. 2004 SNLS TruncatedGold FullGold S. Nesseris, L.P.astro-ph/0511040Phys.Rev.D72:123519,2005 Data Consistent at 95% Flat ΛCDM Consistent with all data Flat SCDM (Ωm=1) rulled out at more than 10σ

  23. Better Fits?

  24. Comparative Analysis for Dynamical Dark Energy Parametrization A of w(z): Parametrization B of w(z):

  25. Comparative Analysis for Dynamical Dark Energy Best Fits for w(z): S. Nesseris, L.P.astro-ph/0511040Phys.Rev.D72:123519,2005

  26. Minimally Coupled Scalar: No w=-1 crossing Homogeneous Minimally Coupled Scalar: +: Quintessence -: Phantom Equation of State: 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. Non-minimal Coupling: Scalar Tensor Theories Non-minimal Coupling Rescale Φ Theory Defined by Minimal Coupling

  28. Cosmological Evolution in Scalar-Tensor Theories Vary ST action in flat FRW background assuming perfect fluid: +

  29. JCAP 0511:010,2005 Crossing w=-1 line Reconstruction from Best Fit to Gold Dataset L.P. astro-ph/0504582, JCAP 0510:001,2005, S. Nesseris, L.P. astro-ph/0502053, 2006 (accepted in Phys. Rev. D) F(Φ) U(Φ) Minimum: Generic feature Φ Φ

  30. SUMMARY • 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. w<-1 Big Rip Bound Systems in Expanding Background: Radial Geodesics: S. Nesseris, L. P., Phys.Rev.D70:123529,2004 Repulsion Increases with time for w<-1 Big Rip Repulsion Explodes at t*~w/(w+1)

  32. w=-1.5 Bound System Dissociation S. Nesseris, L. P., Phys.Rev.D70:123529,2004

  33. Dissociation Bound System w=-1.2 S. Nesseris, L. P., Phys.Rev.D70:123529,2004

  34. Obs Other Dark Energy Probes Gold Gold+CMB+BAO Gold+CMB+BAO+Clusters w Standard Ruler:Sound Horizon (z=zrec,z=0.35) dA(z) from Clusters z Luminosity Distance S. Nesseris, L.P. in preparation Gold+CMB+BAO+Clusters+SNLS Crossing of w=-1consistent withall datasets! Ang. Diameter Distance

  35. Possible Systematic Errors Q: What (other than distance) could be making high-z SnIa dimmer? No! Dust absorbs blue light more than red light. Distant SnIa have similar spectra as nearby SnIa. Could it be Dust? No! The diming does not continue to amplify at z>0.5 Could it be Grey Dust? No! The time evolution of SnIa spectrum is identical for close and for distant SnIa. Could it be Evolution of SnIa?

  36. Why Not Scalar-Tensor Theories Sringent Observational Constraints: Solar System: Cosmology:

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

  38. History of SnIa Results 1. Measurements of the Cosmological Parameters Omega and Lambda from the First 7 Supernovae at z >= 0.35S. Perlmutter et al., Astrophys.J. 483 (1997) 565 2. Observational Evidence from Supernovae for anAccelerating Universe and a Cosmological ConstantS. 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. Evolution of SnIa Results 4. Cosmological results from high-z supernovaeTonry et al. The Astrophysical Journal, 594:1-24, 2003 September 1 5. New Constraints on ΩM, ΩΛ, and w from an Independent Set of 11 High-Redshift Supernovae Observed with the Hubble Space TelescopeR.A. Knop et al., The Astrophysical Journal, Volume 598, Issue 1, pp. 102-137 11 new SnIa observed from HST 6. Type Ia Supernova Discoveries at z > 1 From the Hubble SpaceTelescope: 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 HST7 of them with z>1.25 Decelerating Expansion starts at z=0.46

  40. The Future • 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

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