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Constraining Accelerating Cosmologies with Distance Measures

Constraining Accelerating Cosmologies with Distance Measures. Yu Gao Physics Department, UW-Madison. astro-ph/0611775 , updated with ESSENCE data. In collaboration with Danny Marfatia(Univ. Kansas) & Vernon Barger(UW-Madison). Our universe is…. Expanding: Accelerating :. (Friedman 2001)

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Constraining Accelerating Cosmologies with Distance Measures

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  1. Constraining Accelerating Cosmologies with Distance Measures Yu Gao Physics Department, UW-Madison astro-ph/0611775, updated with ESSENCE data In collaboration with Danny Marfatia(Univ. Kansas) & Vernon Barger(UW-Madison)

  2. Our universe is… • Expanding: • Accelerating: (Friedman 2001) (Sandage 2006) Decelerating parameter …but why ?

  3. Cosmological models • LCDMEinstein’s cosmological constant L withnon-evolutionary dark energy equation of stateDimensionless Friedman equation Wm: Total matter density WK: Curvature density, universe is OPEN if WK<0 or CLOSED if WK>0 WL: Dark energy density

  4. wCDMDark energy equation of state evolves according towCDM Friedman equation (M. Chevallier, D Polarski, 2000) * Spatially flat models: WK= 0 * LCDM: wa= 0 * “Weak prior”, assumes w(z>1.8)= -1 (Riess 06) i.e. outside red-shift range probed by supernovae

  5. Modified gravity? • Braneworld model (Randall & Sundrum 1999)Generically, Problem: Too many free parameters for SN data. • A specific case:DGP (Dvali, Gabadadze & Porrati 2000)Gravitational leakage into 5th bulk dimension over long distance Gravitation withExtra dimension (Sahni, Shtanov 2002)

  6. Hubble expansion in DGP A braneworld case with Where DGP is self-accelerating when Wr >>Wm: (Deffayet, Dvali, Gabadadze, 2001)

  7. Luminosity distance • Probe for cosmological expansion history E(z) • Theoretical: • f: sinh if Wk >0 or sin if Wk<0 • Experimental: 5log10(DL/10) ~ M(absolute luminosity) - m(apparent luminosity) Distance Modulus+correction from SN light curve

  8. Standard Candle • Type-Ia supernovaeExplosion at 1.44 solar mass, Energy ~1046 J consistent absolute luminosity measurable DL • Available datasetsHST Key Project (Riess et.al. 2006)SNLS (Astier et. al. 2005)ESSENCE (Wood-Vasey et. al. 2007) “Nearby SN” at low redshift z < 0.015 (Guy et.al. 2005)

  9. Data compilations Gold set (Riess 2006) 182 Type-Ia SN, z < 1.7, 16 SN z >1 Combined with initial ESSENCE release (Davis 2007) Available at:http://www.ctio.noao.edu/essence192 SN with 15 z >1, Improved SN selection, Reduced uncertainty in distance modulus http://braeburn.pha.jhu.edu/~ariess/R06/

  10. Other Constraints CMB shift parameter (WMAP)Insensitive to models where zCMB=1089 Baryonic acoustic oscillation (SDSS) where zBAO=0.35suitable for stationary DE models (Wang & Mukherjee 2006)

  11. Statistical Analysis • Likelihood function • Marginalization over SN nuisance parameter M (E.Pietro, J. Claeskens, 2002)

  12. Models, constraints and best-fit parameters

  13. * Spatially flat models BAO not included for DGP and models

  14. LCDM, SN+shift parameter(R) LCDM SN+R

  15. LCDM SN+R+B LCDM, SN+BAO+shift parameter(R)

  16. Flat wCDM wa=0, SN+shift parameter(R) wCDM pic

  17. wCDM BAO+SN+R Flat wCDM wa=0, SN+BAO+shift parameter(R)

  18. Flat wCDM,w(z>1.8) = -1, SN+shift parameter(R) Flat wCDM,w(z>1.8)=-1 SN+R

  19. Flat wCDM SN+R Flat wCDM, 0.15< Wm<0.35,SN+shift parameter(R)

  20. DGP SN+R DGP, SN+shift parameter(R)

  21. Conclusion • LCDM fits data very well;All models produces close minimal c2 • Combined analysis prefers flat universe, with slightly positive curvature. What could be more effective probes? Higher redshift objects (GRB) ? CMB spectrum for braneworld models ? … …

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