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L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina Open page
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Directly Observable Dark Energy (Inferred) No Yes Flat Friedmann Equation Not Consistent
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Accelerating Universe: (rate of expansion) was smaller in the past. Thus H -1 (t) was larger in the past.
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z~0.5: Acceleration starts 157 SnIa
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Equation of State: Necessary condition for acceleration:
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(from large scale structure observations)
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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/0511040 Phys.Rev.D72:123519,2005
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What theory produces crossing of the w=-1?
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+: 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:
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Non-minimal Coupling
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Minimum: Generic feature F(Φ) ΦΦ U(Φ) L.P. astro-ph/0504582, JCAP 0510:001,2005, S. Nesseris, L.P. astro-ph/0602053, Phys.Rev.D73:103511,2006 JCAP 0511:010,2005
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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)
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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
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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
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positive energy of gravitons
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G(z)~1/F(z) decreases at recent times thus boosting accelerating expansion Minimum: Generic feature
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