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Is the cosmic acceleration slowing down? Tuo Zhongliang KITPC, CAS April 1st, 2011
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Outline Eternal acceleration or escape eternal acceleration? Cosmographic approach Non-parametrization method Summary
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Riess Perlmutter The accelerating expansion SNIa observations in 1998 find cosmic acceleration.
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Concordance model (LCDM) WMAP7 Dark energy: 73.4% Dark matter: 22.2% Normal matter: 4.4%
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the big rip “Cosmic Doomsday” R.R.Caldwell, M.Kamionkowski and N.N.Weinberg, Phys.Rev.Lett.91(2003)071301
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Can the universe escape eternal acceleration ? J. D. Barrow, R. Bean and J. Magueijo, Mon.Not.Roy.Astron.Soc.316:L41,2000 A difference of 120 orders of magnitude
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Cosmographic approach Redshift expansion y-redshift expansion,
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Thus to reduce the systematic error
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Hubble parameter For z<z cut or y<y cut, For z cut <z<1.0 or y cut <y<1.0,
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Data sets SNeIa: Union2 (R.Amanullah et al. e-Print: arXiv:1004.1711 ) Distance modulus Marginalization over μ 0
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Data sets Hubble parameter (D. Stern et al. e-Print: arXiv:0907.3149 ) Marginalization over H 0
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1-D marginalized probability distribution of q 0
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Evolution behavior of q(z)
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Evolution behaviors of q(z)
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Comparison with the Hubble data
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Non-parametrization method Independent of the calibration
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Reconstructed deceleration parameters
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Summary The universe transited from deceleration from acceleration at higher redshift than what the LCDM model predicts The universe is still in the stage of accelerating expansion SNIa data favor a transient acceleration, even with the Hubble parameter data added in.
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Thanks!
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