1.  Input for fundamental physics  Model independent way to extract information  Known tests (very) sensitive to theoretical priors  challenges to experiment & theory אוניברסיטת בן - גוריון Ram Brustein Determining the nature of DARK ENERGY Irit Maor Paul Steinhardt

2. Focus on: Equation Of State standard GR form Space curvature w = -1/3 Higher tensor invariants Scalar fields Extra dimensions Scale dependent G N Modified Friedman eq. and more, … “never underestimate the creativity of a theorist!” FP model EOS additional possibilities:  Tegmark state finder: Sahni et al.

3. Classic tests measure integrals of EOS background luminosity distance volume angular distance shear fluctuations ISW linear/non-linear growth factors speed of sound  situation unclear: Please help! situation clear

4. For example: Luminosity distance d L vs. redshift z  Textbook form is not sufficient

5. g=  m /(1-  m ) Splitting components off, for example, NR matter (dark and visible)

6. Degeneracy! a)DL b)  DL/DL c)w Q (z) For 9 different EOS Assuming 1. perfect knowledge of  M 2. flat U. Maor et al. (2001)

7. P. Antilogus J. Frieman et al Weller & Albrecht Similar conclusions P. Astier, Kujat et al, E. Linder,... I. Maor et al NOTMEASUREw'NOTMEASUREw'

8. Fast roll – w  ~ +1 Slow roll – w  ~ -1 Oscillations – w  ~ 0 w  +1 possible, easy !!! High sensitivity to choice of theoretical framework and priors »need to keep an open mind about priors: for example restricting w Q >-1 »present experimental results in a way that will allow modifying priors ?use some input from theory to parametrize evolution Practical implications:

9. Breaking the Degeneracy ? I. Combine different types of high precision (~ percent) measurements  about 20% in current value of w Q & not very helpful for time-dependence, but … sensitivity estimates depend on actual value of EOS: away from -1 / large positive w' are best Hard to distinguish between different forms of DE. * partial analysis *

10. DE expected to “disappear” for z > 2 CMB photons travel most of the way through MD U.  No gain compared to “low z” probes Best accuracy for d A from CMB ~ 1% (e.g. 1 st peak)  CMB comparable to future SNIa experiments (  M known+ flat U.+…) For example: CMB + SNIa Maor et al (2002) Maor & Brustein (2003) Frieman et al, Caldwell & Doran,... ╬ Confusion about possible attainable sensitivity of other experiments (shear, volume, growth factor, …)

11. Breaking the Degeneracy ? II. Invent new “local” tests: “move the detector to a different z” III. Accept theoretical input: e.g.: that dark energy is a CC, a specific quintessence model, …

12. Measure z(t) Practical ?? Jimenez & Loeb, Jimenez et al

13. Conclusions Known tests (very) sensitive to theoretical priors  Challenges to Experiment & Theory Need: public access to data  independent combined analysis  explore different priors Need: – either a new “local” test - ??? – or new theoretical input - ??? – or LUCK

16. CMB vs. SN Ia x=z+1 Maor & Brustein (2003)

19. Maor et al astro-ph/0112... Linder, astro-ph/0212...