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

2. L.P. accepted in JCAP (2005)

3. Gold Dataset (157 SNeIa): Riess et. al. 2004

4. What theory produces the features of best parametrizations?

5. +: Quintessence -: Phantom To cross the w=-1 line the kinetic energy term must change sign (impossible for single phantom or quintessence field) Generalization for k-essence:

6. Non-minimal Coupling

11. positive energy of gravitons

14. For U(z)=0 there is no acceptable F(z)>0 in 0<z<2 consistent with the H(z) obtained even from a flat LCDM model.

15. Can not be reproduced by any single field minimally coupled theory Q.: Is there a set Φ(z), F(z),U(z) consistent with the constraints that predicts the best fit w(z) crossing the w=-1 line?

16. Use trial Φ(z) to solve (2) for F(z) with F'(z=0)=0, F(z=0)=1. Select Φ(z) such that F(z)>0 for all z (need Φ'(z) small). Use the resulting f(z) and the best fit q(z) in (1) to find U(z). Invert Φ(z) to find z(Φ). Sustitute z(Φ) in F(z) and U(z) to find F(Φ) and U(Φ). 1 2

17. G(z)~1/F(z) decreases at recent times thus boosting accelerating expansion Minimum: Generic feature

18. F(Φ) ΦΦ U(Φ)

19. (more data are needed eg δ m (z)) (best fit H(z) must be rederived fiting M(z) with new parameters)

21. SnIa peak luminosity: SnIa Absolute Magnitude Evolution: SnIa Apparent Magnitude: with: Parametrizations:

23. Φ' 2 changes sign!

24. An observationally viable scalar tensor theory that predicts an H(z)-w(z) crossing the w=-1 line was explicitly reconstructed. The reconstructed theory is not uniquely determined from H(z). The SnIa data can be utilized to simulatneously fit for both H(z) and the Newton's constant G(z) in the context of scalar tensor theories. This can lead to a uniquely defined reconstruction process.