Is the cosmic acceleration slowing down? Tuo Zhongliang KITPC, CAS April 1st, 2011

Outline  Eternal acceleration or escape eternal acceleration?  Cosmographic approach  Non-parametrization method  Summary

Riess Perlmutter The accelerating expansion SNIa observations in 1998 find cosmic acceleration.

Concordance model (LCDM) WMAP7 Dark energy: 73.4% Dark matter: 22.2% Normal matter: 4.4%

the big rip “Cosmic Doomsday” R.R.Caldwell, M.Kamionkowski and N.N.Weinberg, Phys.Rev.Lett.91(2003)071301

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

Cosmographic approach Redshift expansion y-redshift expansion,

Thus to reduce the systematic error

Hubble parameter For z<z cut or y<y cut, For z cut <z<1.0 or y cut <y<1.0,

Data sets SNeIa: Union2 (R.Amanullah et al. e-Print: arXiv: ) Distance modulus Marginalization over μ 0

Data sets Hubble parameter (D. Stern et al. e-Print: arXiv: ) Marginalization over H 0

1-D marginalized probability distribution of q 0

Evolution behavior of q(z)

Evolution behaviors of q(z)

Comparison with the Hubble data

Non-parametrization method Independent of the calibration

Reconstructed deceleration parameters

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.

Thanks!