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Can we detect tracking dark energy dynamics?

Can we detect tracking dark energy dynamics?. Bruce Bassett, Mike Brownstone, Antonio Cardoso, Marina Côrtes, Yabebal Fantaye, Renee Hlozek, Jacques Kotze, Patrice Okouma. arXiv:0709.0526. Big Bang Nucleosynthesis.

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Can we detect tracking dark energy dynamics?

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  1. Can we detect tracking dark energy dynamics? Bruce Bassett, Mike Brownstone, Antonio Cardoso, Marina Côrtes, Yabebal Fantaye, Renee Hlozek, Jacques Kotze, Patrice Okouma arXiv:0709.0526

  2. Big Bang Nucleosynthesis • Hence we can constrain the amount of dark energy at BBN. Bean et al. (2001) find at 2s • CMB constraints (Doran et al. 2005, 2006) from the power spectrum give arXiv:0709.0526

  3. Tracking Models DE Dominated Matter dominated Radiation dominated Slow transition Perfect scaling Where the field stops tracking and starts to dominate arXiv:0709.0526

  4. Linking BBN to late times • Tracking Dark Energy models link the constraints on DE at z = 1010 to today via the energy density of DE arXiv:0709.0526

  5. Hubble Parameter arXiv:0709.0526 as zt →∞, r → 0

  6. Specific late-time models • Two broad classes of tracking models considered – polynomial w(z) and scalar field φ in a double exponential potential • Polynomial: • Linear case (w2=0) → zt≈ 6.2 arXiv:0709.0526

  7. Quadratic Case • If w2≠0 then w(zt)=0 → w(0) = -1 zt > 4.02 to ensure w(z) ≥-1 w< -0.8 for all z< 1 arXiv:0709.0526

  8. Dark Energy Density arXiv:0709.0526

  9. H(z) - quadratic 2.7% arXiv:0709.0526

  10. Δμ(z) - quadratic DETF Stage III errors between 0.02 and 0.3 mag DETF Stage IV (SNAP-like) Errors ~ 0.01mag Deviation →0.03 mag as z →∞ arXiv:0709.0526

  11. Double Exponential Potential • Not perfect scaling: the BBN constraint is now arXiv:0709.0526

  12. Double Exponential Potential • Two cases: • m >0 → smooth w(z) at low redshift • m < 0 → oscillating w(z) arXiv:0709.0526

  13. Double Exponential Potential arXiv:0709.0526

  14. Double Exponential Potential arXiv:0709.0526

  15. Double Exponential Potential Field φ oscillates around minimum arXiv:0709.0526

  16. Double Exponential Potential arXiv:0709.0526

  17. Double Exponential Potential arXiv:0709.0526

  18. Double Exponential Potential Late-time Acceleration with smooth w(z) Early scaling arXiv:0709.0526

  19. Derived w(z) from Double Exponential V(φ) All models have w<-0.98 for z<0.2 arXiv:0709.0526

  20. Energy Density - DEP 3/4e arXiv:0709.0526

  21. H(z) - DEP Forcing w(0) < -0.9 means deviation < 2.5% arXiv:0709.0526

  22. Δμ(z) - DEP All oscillating models have |Δμ| <0.032 Solid line → w(0) = -0.9 model arXiv:0709.0526

  23. Failure of standard parametrisations • Chevalier-Polarski-Linder parametrisation is most widely used • Forms the basis for the DETF Figure of Merit • If φ is to be a minimally coupled canonical scalar field → w(z) ≥ -1 for all z • CPL cannot match both BBN and have w(z) ≥ -1 • Logarithmic w(z) works, but requires zt > 12.4 arXiv:0709.0526

  24. CPL Energy Density Phantom w needed to match the BBN constraints arXiv:0709.0526

  25. Conclusions • Detection of tracking dynamics will be limited until Stage IV experiments • The standard CPL parametrisation cannot match BBN when describing fields with w(z) ≥ -1 arXiv:0709.0526

  26. Conditions on models • So if w large today it must stay flat: • In all our models • For the linear parametrisation we find arXiv:0709.0526

  27. w(0) – w’(0) connection • Empirical relation for other models? • To be considered in more detail in future work arXiv:0709.0526

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