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Spanish Relativity Meeting 2008, Salamanca, September 15-19 (2008)

Avoiding the DARK ENERGY coincidence problem with a COSMIC VECTOR. Antonio L. MAROTO and Jose BELTRÁN JIMÉNEZ Universidad Complutense de Madrid. Phys. Rev. D 78, 063005 (2008). Spanish Relativity Meeting 2008, Salamanca, September 15-19 (2008).

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Spanish Relativity Meeting 2008, Salamanca, September 15-19 (2008)

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  1. Avoiding theDARK ENERGY coincidence problemwith a COSMIC VECTOR Antonio L. MAROTO and Jose BELTRÁN JIMÉNEZ Universidad Complutense de Madrid Phys. Rev. D 78, 063005 (2008) September 15-19, 2008 Spanish Relativity Meeting 2008, Salamanca, September 15-19 (2008)

  2. The accelerated expansion of the universe dL(z) relation from SN Ia data • Supernova Cosmology Project: 42 SNe Ia, z<0.83 • High-z Supernova Search Team: 14 SNe Ia, z < 0.62, 1998 Hubble Space Telescope (Gold Set): 157 SNe Ia, + 16 with z > 1.25. Deceleration - acceleration transition at z>0.46 ±0.13 2004 Accelerated Decelerated-accelerated Decelerated SNLS 71 SNe Ia z < 1 Reduced systematics (single instrument) 2005 September 15-19, 2008

  3. The need for dark energy Einstein’s equations in flat FRW backgrounds Friedmann equation Acceleration requires negative pressure: DARK ENERGY September 15-19, 2008

  4. The need for dark energy Dark energy equation of state pDE = wDE rDE wDE= const. Flat models (WM +WDE = 1) SNLS set Gold set Gold Set Favors wDE < -1 September 15-19, 2008

  5. The need for dark energy Crossing the phantom divide wDE < -1? wDE= wDE(z) ODEP: CMB, BAO, growth factor Gold Set Nesseris, Perivolaropoulos, ‘07 September 15-19, 2008

  6. The dark energy coincidence problem Cosmological constant pL= - rL Gmn= 8pG(Tmn+Lgmn) L~ (10 - 3 eV) 4 G = (1019 GeV)-2 Coincidence problem September 15-19, 2008

  7. The dark energy coincidence problem Quintessence: scaling regime M has to be fixed in order to getWDE Scaling September 15-19, 2008

  8. The dark energy coincidence problem Why rDE ~ rMtoday ? Dark Energy models (L, scalar, f(R),…) require unnatural dimensional parameters in their Lagrangians or initial conditions • Our aim is to find a model: • without dimensional scales (apart from G), • with the same number of parameters as LCDM, • with natural initial conditions, • with good fits to SNIa data Vector models can do the job ! September 15-19, 2008

  9. The model Vector-tensor action • Gonly dimensional scale in the model • No free parameters • No potential terms (Kiselev,Armendariz, ’04, Boehmer, Harko ’07, • Mota, Koivisto `07) September 15-19, 2008

  10. The model Equations of motion Flat Robertson-Walker metric September 15-19, 2008

  11. The model Explicit solutions: radiation and matter eras Radiation Matter Scaling during radiationera September 15-19, 2008

  12. Energy densities Radiation Final singularity Vector dark energy Matter Cosmological constant Scaling September 15-19, 2008

  13. Equation of state Vector field evolution (MP units) W=1/3 W= -0.457 phantom line Radiation September 15-19, 2008

  14. Fitting SNe type Ia data Luminosity distance Distance modulus Data sets Gold (Riess et al ’04) z<1.7 SNLS (Astier et al. ’06) z<1 157 (previous)+ 16 (HST z>1) = 173 SNe 44 (previous)+ 71 (new z<1) = 115 SNe September 15-19, 2008

  15. Fitting SNe type Ia data: VCDM vs. LCDM Gold set September 15-19, 2008

  16. Other parametrizations with the Gold set VCDM: Vector dark energy: best fit to Gold dataset to date Lazkoz, Nesseris, Perivolaropoulos, ‘05 September 15-19, 2008

  17. Initial conditions and the end of the universe Natural initial conditions: “Imminent” final singularity: Type III “Big-freeze” singularity tend –t0 = 690 million years (h=0.7) ~ earliest fossils Nojiri, Odintsov, Tsujikawa, ‘05 Bouhmadi, González, Martin, ’07 September 15-19, 2008

  18. Stability and local gravity tests PPN parameters Static parameters agree with GR Preferred frame effects Present bounds Will, ’81, Nordtvedt Classical stability Real propagation speed for scalar, vector and tensor perturbations Quantum stability: ghosts? September 15-19, 2008

  19. Conclusions • Vector model for dark energy with: • No potential terms • No dimensional scales (apart from G) • No free parameters • Standard kinetic terms Scaling behaviour during radiation and natural initial conditions (No coincidence problem) Excellent fit to Gold dataset and compatible with SNLS: definite predictions for cosmological parameters Phantom dark energy today: BAO, CMB? September 15-19, 2008

  20. Evolution of density perturbations Sub-Hubble modes Matter or radiation eras Radiation era Matter era PRELIMINARY Density contrast (matter and radiation) September 15-19, 2008

  21. Evolution of density perturbations Super-Hubble modes Matter and radiation eras PRELIMINARY Density contrast (matter and radiation) September 15-19, 2008

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