L. Perivolaropoulos http://leandros.physics.uoi.gr

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Open page
A Comparison of
Dark Energy Probes

• L. Perivolaropouloshttp//leandros.physics.uoi.gr
  
• Department of Physics
• University of Ioannina

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Structure of Talk
Introduction - Key Questions - Latest Data
Standard Rulers vs Standard Candles Constraints
Comparison
Gamma Ray Bursts as Standard Candles
Current Dynamical Constraints Growth Rate from
redshift distortion Weak Lensing
Potential Constraints from Laboratory
Experiments Signatures of a vacuum energycutoff
in the Casimir Effect
Conclusions
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Candidate Model Classes
Cosmological Constant
Expansion History
G?? - ? g?? ??T??
Dark Energy
G?? ???Tm????Tµ?)
Allowed Sector
Eq. of state evolution
Forbidden(ghosts)
Modified Gravity
G?? ??Tm??
Allowed Sector
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Key Questions
Is General Relativity the correct theory on
cosmological scales?
What is the most probable form of w(z) and what
forms of w(z) can be excluded?
Is ?CDM (GR ?) consistent with all cosmological
observations?
What is the recent progress?
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Accelerating Expansion Latest Constraints
Latest data (307 SnIa) Kowalski et. al.
arXiv0804.4142
Recent data Wood Vasey et. al. astro-ph/0701041

4 years ago Riess et. al. astro-ph/0402512Astrop
hys.J.607665-687,2004
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Accelerating Expansion Latest Constraints
4 years ago Riess et. al. astro-ph/0402512Astrop
hys.J.607665-687,2004
Latest data (307 SnIa) Kowalski et. al.
arXiv0804.4142
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Progress Report
Is ?CDM (GR ?) consistent with all cosmological
observations?
Yes! Flat, ?CDM remains at 1s distance from the
best fit since 2004.
The 1s parameter contour areas remain about the
same since 2004 despite of the double size of the
SnIa sample and ?CDM remains at the lower right
part of the (w0,wa) contour!
Q Which Dark Energy Probe has the weakest
consistency with ?CDM?
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Geometric Constraints
Parametrize H(z)
Minimize
WMAP3SDSS(2007) data
ESSENCESNLSHST data
Standard Candles (SnIa)
Lazkoz, Nesseris, LPJCAP 0807012,2008. arxiv
0712.1232
2s tension between standard candles and standard
rulers
Standard Rulers (CMBBAO)
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Gamma Ray Bursts
Gamma-ray bursts (GRBs) The most luminus
electromagnetic events (1052 ergs/secmass of
Sun) occurring in the universe since the Big Bang
Collimated emissions (0.1-100 seconds long)
caused either by the collapse of the core of a
rapidly rotating, high-mass star into a black
hole or from merging binary systems (short
bursts).
GRBs are extragalactic events, observable to the
limits of the visible universe a typical GRB has
a z gt 1.0 while the most distant known
(GRB080913) has z6.7
Swift Satellite (2004)
Shells of energy and matter ejected by the
newly-formed hole collide and merge ("internal
shocks"). The shell sweeps up more and more
material it slows down and releases energy
(afterglow).
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GRB Correlations
GRBs are not standard candles but may be
calibrated using empirical correlation relations
between energy output and lightcurve measurable
observables.
Example of Correlation
Steps for cosmological fitting (Schaefer
astro-ph/0612285, Hong Li et. al.
Phys.Lett.B65895-100, 2008)
1. Assume
Schaefer astro-ph/0612285
or
and fit for a, b using a specific cosmological
model to find Li
2. Use the fitted a, b to find the correct Li
from the observed Epeak i
L obtained from
3. Use the new Li , along with li, zi to fit
cosmological parameters
Circularirty problem A cosmological model has
been used to calibrate a, b !!
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Fixing the Circularity Problem
S. Basilakos, LP, arXiv0805.0875,accepted in
MNRAS (to appear)
Fit a, b along with the cosmological parameters
(eg Om)
Minimize ?2 wrt a, b, Om
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GRB vs Other Probes
Current GRB data are not competitive with other
geometric probes. The calibration has too much
scatter and there are additional parameters to be
fit.
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Dynamical Probes I Redshift Distortion
The power spectrum at a given redshift is
affected by systematic differences between
redshift space and real space measurements due to
the peculiar velocities of galaxies.
Galaxy power spectrum in redshift space
Galaxy power spectrum in real space space
µcos? and ? is the angle between and the
line of sight.
Find f
Measure ß
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Dynamical Constraints
Measure growth function of cosmological
perturbations
Evolution of d
Parametrization
Fit to LSS data
?CDM
?CDM provides an excellent fit to the linear
perturbations growth data
best fit
S. Nesseris, LP, Phys.Rev.D77023504,2008
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Dynamical Probes II Weak Lensing
L. Fu et al. Very weak lensing in the CFHTLS
Wide, arxiv. 0712.0884
Non-gravitational
Use weak lensing to observe the projected dark
matter power spectrum (cosmic shear spectrum) and
compare with ?CDM predictions using maximum
likelihood.
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The Experimental Effects of a Cutoff
Cutoff
EM vacuum energy with cutoff (allow for compact
extra dimension)
Density of Modes is Constant.Energy of Each Mode
Increases.Force becomes repulsive!
Required Cutoff
With Cutoff
Compact Extra dim, No cutoff
LP, Phys. Rev. D 77, 107301 (2008)
No extra dim.
Poppenhaeger et. al.hep-th/0309066
Phys.Lett.B5821-5,2004
with compact extra dim
The cutoff predicts a Casimir force which becomes
repulsive for dlt0.6mm
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SUMMARY
After the Golden Age 1998-2005 of new dark
energy observational constraints, the improvement
of these constraints has slowed down.
The most probable probe that may lead to disfavor
of ?CDM in the next few years appears to be
observations of Baryon Acoustic Oscillations
Laboratory Experiments related to Casimir effect
have the potential to reveal useful signatures of
a physical cutoff associated with vacuum energy .
dark energy
cmb
No. of papers with words dark energy and CMB
in title per year (from spires database
http//www-spires.dur.ac.uk/spires/hep/