L. Perivolaropoulos Department of Physics University of Ioannina Open page.

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Presentation transcript:

L. Perivolaropoulos Department of Physics University of Ioannina Open page

Directly Observable Dark Energy (Inferred) No Yes Flat Friedmann Equation Not Consistent

Accelerating Universe: (rate of expansion) was smaller in the past. Thus H -1 (t) was larger in the past.

z~0.5: Acceleration starts 157 SnIa

Equation of State: Necessary condition for acceleration:

(from large scale structure observations)

Gold dataset Riess -et. al. (2004) SNLS dataset Astier -et. al. (2005) Other data: CMB, BAO, LSS, Clusters Gold dataset Riess -et. al. (2004) SNLS dataset Astier -et. al. (2005) Other data: CMB, BAO, LSS, Clusters S. Nesseris, L.P. in prep. Other data: CMB, BAO, LSS, Clusters S. Nesseris, L.P. astro-ph/ Phys.Rev.D72:123519,2005

What theory produces crossing of the w=-1?

+: 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:

Non-minimal Coupling

Minimum: Generic feature F(Φ) ΦΦ U(Φ) L.P. astro-ph/ , JCAP 0510:001,2005, S. Nesseris, L.P. astro-ph/ , Phys.Rev.D73:103511,2006 JCAP 0511:010,2005

Growth Factor: Growth Factor Evolution (Linear-Fourier Space): General Relativity: DGP: Scalar Tensor: Modified Poisson: Koyama and Maartens (2006) Sealfon et. al. (2004) Esposito-Farese and Polarski (2001) Uzan (2006)

ΛCDM (SnIa best fit, Ω m =0.26 ) DGP SnIa best fit + Flat Constraint Scalar Tensor (α=-0.5, Ω m =0.26 ) Flat Matter Only S. Nesseris, L.P. in prep. Verde et. al. MNRAS 2002 Hawkins et. al. MNRAS 2003

The Expansion of the Universe is currently accelerating. This acceleration can be modeled either by a Dark Energy or by Extended Gravity Theories. All recent data indicate that w(z) is close to -1. Thus w(z) may be crossing the w=-1 line. Minimally Coupled Scalar predicts no crossing of w=-1 line Scalar Tensor Theories are consistent with crossing of w=-1 Extended Gravity Theories (DGP, Scalar Tensor etc) predict unique signatures in the growth rate of cosmological perturbations

positive energy of gravitons

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