Title: Dynamical Dark Energy: Future constraints from cosmic complementarity and weak lensing tomography a
1Dynamical Dark Energy Future constraints from
cosmic complementarity and weak lensing
tomography (a critical discussion)
- Mustapha Ishak
- Princeton University(M. Ishak and D. Spergel
2004) - (Work supported by NASA ATP grant and NSERC
Fellowship) - (A. Upadhye, M. Ishak and P. Steinhardt, 2004)
2Motivation
- Look for clues on how to address and try to solve
the dark energy problems - Among problems associated with dark energy
- What is it? A cosmological constant? Or a
dynamical component? Or neither (cosmic
acceleration due to modified gravity)? - Why is the value measured from cosmology so small
compared to QFT calculations? - Why did it become dominant during the present
epoch? (timing problem)
3Parameterizing Dark EnergyThe equation of state
(EOS)
- The equation of state two levels of difficulty
- A constant EOS with w only
- A dynamical component with w(z)
4Probing the dark energy density(less model
dependent)
- Density as a continuous interpolated function
(see Wang Freese 2004) - 2 dimensionless density amplitude parameters ei
?de(zi)/ ?de(0)
5 Constraints on w0 w1 from currently available
data
6 Constraints on w0 w1 from currently available
data
7Current constraints a summary
- Current data seems to favor a cosmological
constant when a constant EOS is assumed - Not possible to constrain dynamical models
conclusively using currently available data - In general, the central values w0lt-1 and w1gt0
- Recently, central values closer to a cosmological
constant but we will see with the WMAP-2 analysis
8How much better are we going to do in the
near/far future?
- A powerful trio SNWLCMB
- breaks various degeneracies between various
cosmological parameters
9Methods and analyses I
- Study 1 (Upadhye, Ishak and Steinhardt, 2004)
- Monte-Carlo simulations of SN (2200), WL
(fsky0.7, n56 gal/arcmin2) and WMAP 8 year
data. - chi2 minimization, used vanilla model (w0, w1,
zs) - No strong priors assumed
- Applied the analysis to currently available data
then to simulated future data
10Methods and analyses II
- Study 2 (Ishak and Spergel, 2004)
- Used 2200 SN
- WL surveys with and without tomography
- WMAP-8, PLANK, ACTWMAP-8
- Used Fisher formalism (results are consistent
with previous study for the WMAP-8 case) - 10 cosmological parameters 3 systematic
parameters considered (we added T/S, running, WL
calibration parameters) - 2 EOS parameterizations and 1 density
parameterization - 2 WL surveys ground-based like survey with 2
bin tomography space-based like deep survey
with 10 bin tomography
11Summaryof ourresults(Study I) and
otherstudyresults
12First conclusions
- The constraints we obtained without tomography
and the ones published from other studies are not
enough to rule out dynamical dark energy models - The remaining uncertainty is roughly 0.10 at
the one sigma level - We require errors of 0.02 by comparison with
the case of WMAP spatial curvature Ototal1.02
0.02
13Plot ICosmiccomplementarityCMB,SNeIa,and
WL
14Table II weak lensing adds a factor of two
improvement to PlanckSN0.8, but still not
enough
15Table III same but for the second
parameterization
1610 bin tomography could make the necessary
improvement
17Plot IIWL tomography.Constraints on the
EOSparameters
18Discussion surveys
- The desirable level of precision (0.02 say, on
all the DE parameters) seems possible from
PlanckSN1.5WLT10 (very large fraction of
the sky, multiple bin tomography) - Results suggest that more ambitious and more
sophisticated weak lensing surveys than what has
been proposed are required (perhaps currently
proposed experiments need to be enhanced)
19Discussion systematic effects
- Some have been included in the analysis (for SN
magnitude uncertainty, WL calibration, and source
redshift distribution) - But more need to be done intrinsic alignments,
non-linear matter power spectrum calculation, - These need to be well understood and tightly
controlled in order to achieve the targeted level
of precision
20What is needed?
- More ambitious and sophisticated weak lensing
surveys with very large fraction of the sky and
many bin tomography. - So, is this the way to go?
21Conclusions
- Although there are some worries about
systematics, our study suggests that
PlanckSN1.5 ambitious weak lensing
tomography (very large fractions of the sky and
many redshift bins) can add KEY improvements to
the dark energy parameter constraints (0.02) - Using less ambitious surveys, we will be able to
distinguish between some competing models
(quintessence trackers, SUGRA models) but we will
not be able to exclude all dynamical dark energy
models - Also, one should keep in mind that even in the
case that (0.02) will be achieved in the far
future, finding w0-1 and w10 will not solve the
cosmological constant problems but confirm them. - Therefore, in addition to current plans, other
types of TESTS or measurements seem necessary to
constrain decisively the true nature of dark
energy. - Testing the nature of dark energy beyond the
equation of state or the density parameters may
be the way to go Weak lensing is a promising
tool for such tests (as it probes the expansion
history the growth factor of LSS)