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Dark Energy in The Context of Large Data Sets

Dark Energy in The Context of Large Data Sets. Patrice M. OKOUMA UCT/SAAO/AIMS December, 30th 2010 SKA Bursary conference/Stellenbosch. Outline. Paper I : A Fundamental uncertainty in The BAO scale from Isocurvature modes

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Dark Energy in The Context of Large Data Sets

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  1. Dark Energy in The Context of Large Data Sets Patrice M. OKOUMA UCT/SAAO/AIMS December, 30th 2010 SKA Bursary conference/Stellenbosch

  2. Outline Paper I : A Fundamental uncertainty in The BAO scale from Isocurvature modes (based upon arXiv:1006.4687v1 : submitted ) Paper II : A Fundamental Uncertainty on The Cosmic Curvature From Dark Energy ? ‏

  3. Paper I : A Fundamental uncertainty in The BAO scale from Isocurvature modes (based upon arXiv:1006.4687v1 : submitted )‏ Work with C. Zunckel, S.M. Kasanda, K. Moodley, (UKZN) & B.A. Bassett (UCT/SAAO/AIMS)‏ • Initial conditions & Baryon Acoustic Oscillations (BAO)‏ in brief • Fisher formalism applied to galaxy power spectrum • Current result‏(s)‏ • Summary

  4. Motivation “ (...) The SKA will assemble a large enough sample of galaxies to measure BAOs as a function redshift to constrain the equation of state of dark energy (...) “ T. Joseph W. Lazio, arxiv:0910.0632v1 (The SKA)‏ -------->our current understanding of BAO relies on a set of restrictive assumptions about the initial conditions. Question : Assuming more general initial conditions, by how muchcould this assumption alter/bias our understanding of DE via the BAO scale ?

  5. Initial Conditions Adiabatic (curvature) perturbations Isocurvature (entropy) perturbations space space

  6. “ Fingerprints ” on Large Scale Structure

  7. Eisenstein et al. (2005)‏ In adiabatic mode : r0 r0 r0 = Standard ruler

  8. Fisher formalism applied to galaxy power spectrum If likelihood function of band powers of galaxy power spectrum is Gaussian : (Tegmark et al. 1997; Seo & Eisenstein 2003)‏

  9. Fisher formalism applied to galaxy power spectrum – cont'd + Isocurvature parameters Gaussian Likelihood = Minimum error on parameter

  10. FoM alterations for stage III-IV -like survey parameters 1.5, 1.2

  11. Bias in DE params. estimates for stage III-IV -like survey parameters 7σ (10σ) incorrect measurement of Wo and as much as 23σ (12σ) for Wa if ignoring isocurvature modes

  12. Summary • BAO are a firm prediction of CDM models • and one key-topic of the science programme for SKA ; • If one does not allow for general initial condition, one can get • very large biases in dark enerrgy parameters for future BAO • surveys such as SKA

  13. More at :arxiv.org/abs/1006.4687

  14. Paper II : A Fundamental Uncertainty on The Cosmic Curvature From Dark Energy ? Work with Y. Fantaye (SISSA, Italy) & B.A. Bassett (UCT/SAAO/AIMS)‏ Outline • The cosmic curvature/dark energy dynamics degeneracy • A Monte Carlo based exploration with the cosmomc code • Current result‏(s)‏ • Summary & work in progress

  15. The cosmic curvature/dark energy degeneracy D. Larson et al. (2010)‏ l1

  16. A Monte Carlo based exploration via the cosmomc code with a general evolution for the dark energy

  17. Current resut(s) Okouma et al. in prep.

  18. Summary & work in progress • Measuring Ωk accurately (σ < 0.003) will play an important role • in the quest to hunt down the true origin of dark energy in the • coming decade. • If one allows for a completely general dark energy • dynamics, then distance measurements alone cannot constrain the • curvature of the universe. • Our preliminary results suggest that the CMB does give good • constraints on curvature, even allowing up to 20 dark energy • parameters; which gives confidence in our belief that • the universe is close to being flat; • Possible artificial cuts ? ; W_i = W(z = z_i) constraints

  19. THANK YOU

  20. Back up slides start here

  21. Current resut(s)

  22. The cosmic curvature/dark energy degeneracy C. Clarkson et al. 2010

  23. A Monte Carlo based exploration with the cosmomc code in the context of a general evolution for the dark energy W_i a_i

  24. Summary & future work • Measuring accurately ( )‏ • will play an important role in the quest to hunt down the true • origin of dark energy in the coming decade. Baryon Acoustic • Oscillations, in conjunction with complementary cosmic probes • are likely to play a leading role ; • Based on a Monte Carlo scheme, our current estimates • on are still inconclusive and further investigations are ongoing ; • The present work may reinforce the growing • recommendation that cosmic curvature must be included • as a free parameter in all future studies of dark energy such • SKA.

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