Is the cosmic acceleration Is the cosmic acceleration slowing down?slowing down?

Tuo ZhongliangTuo Zhongliang

KITPC, CASKITPC, CASApril 1st, 2011April 1st, 2011

OutlineOutline

Eternal acceleration or escape eternal acceleratiEternal acceleration or escape eternal acceleration?on?

Cosmographic approachCosmographic approach

Non-parametrization method Non-parametrization method

SummarySummary

Riess

Perlmutter

The accelerating expansionThe 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 parameterHubble parameterFor z<zcut or y<ycut,

For zcut<z<1.0 or ycut<y<1.0,

Data setsSNeIa: Union2 (R.Amanullah et al. e-Print: arXiv:1004.1711 )

Distance modulus

Marginalization over μ0

Data setsHubble parameter (D. Stern et al. e-Print: arXiv:0907.3149 )

Marginalization over H0

1-D marginalized probability distribution of q1-D marginalized probability distribution of q00

dL zdL y

0 .8 0 .6 0 .4 0 .2 0 .0 0 .20 .0

0 .2

0 .4

0 .6

0 .8

1 .0

q 0

Pq 0

dLH zdLH y

1 .0 0 .8 0 .6 0 .4 0 .2 0 .00 .0

0 .2

0 .4

0 .6

0 .8

1 .0

q 0

Pq 0

Evolution behavior of q(z)Evolution behavior of q(z)

Evolution behaviors of q(z)Evolution behaviors of q(z)

dLH z

C D M

0.2 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 3

2

1

0

1

2

3

z

q

dLH y

C D M

0.2 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 3

2

1

0

1

2

3

z

q

dL z C D M

0.2 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 3

2

1

0

1

2

3

z

q

dL y C D M

0.2 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 3

2

1

0

1

2

3

z

q

Comparison with the Hubble dataComparison with the Hubble data

CD M

dL zdL ydL

H zdLH y

0 .0 0 .2 0 .4 0 .6 0 .8 1 .0

1 .0

1 .5

2 .0

2 .5

z

HzH 0

Non-parametrization methodNon-parametrization method

Independent of the calibration

Reconstructed deceleration parametersReconstructed deceleration parameters

CD M

dL zdL ydL

H zdL

H y

0 .0 0 .2 0 .4 0 .6 0 .8 1 .0

4

2

0

2

4

6

z

qz

SummarySummary

The universe transited from deceleration from acThe universe transited from deceleration from acceleration at higher redshift than what the LCDM celeration at higher redshift than what the LCDM model predictsmodel predicts

The universe is still in the stage of accelerating eThe universe is still in the stage of accelerating expansionxpansion

SNIa data favor a transient acceleration, even wiSNIa data favor a transient acceleration, even with the Hubble parameter data added in.th the Hubble parameter data added in.

Thanks!Thanks!