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
The accelerating expansion
SNIa observations in 1998 find cosmic acceleration.
Riess
Perlmutter
Concordance model (LCDM)
WMAP7
Dark energy: 73.4%
Dark matter: 22.2%
Normal matter: 4.4%
the big rip
R.R.Caldwell, M.Kamionkowski and N.N.Weinberg, Phys.Rev.Lett.91(2003)071301
“Cosmic Doomsday”
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<zcut or y<ycut,
For zcut<z<1.0 or ycut<y<1.0,
Data sets
SNeIa: Union2 (R.Amanullah et al. e-Print: arXiv:1004.1711 )
Distance modulus
Marginalization over μ0
Data sets
Hubble parameter (D. Stern et al. e-Print: arXiv:0907.3149 )
Marginalization over H0
1-D marginalized probability distribution of q0
1.0
dL z
0.8
dL y
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
1.0
0.2
dLH z
q0
dLH y
0.8
0.6
P q0
P q0
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
q0
0.2
0.0
Evolution behavior of q(z)
Evolution behaviors of q(z)
3
2
1
1
0
0
1
1
2
2
3
0.2 0.0
0.2
dL y
CDM
2
q
q
3
dL z
CDM
0.4
0.6
0.8
3
1.0
0.2 0.0
0.2
0.4
z
3
1
0
0
1
1
2
2
0.2 0.0
0.2
0.4
z
1.0
0.6
0.8
1.0
H
dL y
CDM
2
q
q
3
1
3
0.8
z
dLH z
CDM
2
0.6
0.6
0.8
1.0
3
0.2 0.0
0.2
0.4
z
Comparison with the Hubble data
CDM
dL z
2.5
dL y
H
H z H0
dL
H
dL
2.0
z
y
1.5
1.0
0.0
0.2
0.4
0.6
z
0.8
1.0
Non-parametrization method
Independent of the
calibration
Reconstructed deceleration parameters
6
CDM
dL z
dL y
4
H
dL
z
dL
y
H
qz
2
0
2
4
0.0
0.2
0.4
0.6
z
0.8
1.0
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!