Input for fundamental physics Model independent way to extract information Known tests (very) sensitive to theoretical
priors challenges to experiment & theory
אוניברסיטת בן-גוריון
Ram Brustein
Determining the nature ofDARK ENERGY
Irit MaorPaul Steinhardt
0)(3
)(4
83 2
pH
pGH
GH
N
N
Focus on: Equation Of State
standard GR form
Space curvature w = -1/3Higher tensor invariants Scalar fieldsExtra dimensionsScale dependent GN
Modified Friedman eq.• and more, …“never underestimate the creativity of a theorist!”
22 3
2
3
1
3
21
a
aa
H
Hpw
T
TT
FP model EOS additional possibilities: Tegmark
state finder: Sahni et al. 0|0| , tt aa
Classic tests measure integrals of EOSbackground
• luminosity distance
• volume
• angular distance
• shearfluctuations• ISW• linear/non-linear growth factors• speed of sound
z
xH
dxr
1
1 )(
rzdL )1(
)1/( zrdA
)()()( zrzHz
zAP
Hrdz
dV/2
situation unclear: Please help!
situation clear
For example:Luminosity distance dL vs. redshift z
20
2
0)(
ln)1(3ln
0)1(3
H
H
zdwd
wH
T
T
TT
TTT
Textbook form is not sufficient
g= m /(1- m)
z
Q
Q
Qm
Qm
Q
T
TT
xdxwg
wpppw
1
1
ln)(3exp11/
/
Splitting components off, for example, NR matter (dark and visible)
Degeneracy!
a) DLb) DL/DLc) wQ (z)For 9 different EOS
Assuming 1. perfect knowledge of M
2. flat U.
Maor et al. (2001)
P. Antilogus
J. Frieman et al
Weller & Albrecht
Similar conclusions P. Astier, Kujat et al, E. Linder, ...
I. Maor et al
NOT
MEASURE
w'
V
Vpw
2
21
221
Fast roll – w ~ +1Slow roll – w ~ -1Oscillations – w~ 0
w < -1, w > +1 possible, easy !!!
KVVK
VK9
1110
High sensitivity to choice of theoretical framework and priors
» need to keep an open mind about priors: for example restricting wQ>-1
» present experimental results in a way that will allow modifying priors
? use some input from theory to parametrize evolution
Practical implications:
Breaking the Degeneracy ?
I. Combine different types of high precision (~ percent) measurements
about 20% in current value of wQ & not very helpful for time-dependence, but …
• sensitivity estimates depend on actual value of EOS: away from -1 / large positive w' are best
• Hard to distinguish between different forms of DE.
* partial analysis
*
• DE expected to “disappear” for z > 2• CMB photons travel most of the way through MD U.
No gain compared to “low z” probes
• Best accuracy for dA from CMB ~ 1% (e.g. 1st peak)
CMB comparable to future SNIa experiments
(M known+ flat U.+…)
For example: CMB + SNIaMaor et al (2002)Maor & Brustein (2003)Frieman et al, Caldwell & Doran, ...
╬ Confusion about possible attainable sensitivity of other experiments (shear, volume, growth factor, …)
Breaking the Degeneracy ?
II. Invent new “local” tests:
“move the detector to a different z”
III. Accept theoretical input:
e.g.: that dark energy is a CC,
a specific quintessence model, …
Measure z(t)
)()(1 0
ta
atz
Hztz )1()(
HzHztz )1()(
223 )1( HwH T
1)1()1(
)( 23
2
Twz
ztz
35
232 )(
)1( z
tzzwT
Practical ??
Jimenez & Loeb, Jimenez et al
ConclusionsKnown tests (very) sensitive to theoretical priors
Challenges to Experiment & Theory
• Need: public access to data independent combined analysis explore different priors
• Need:– either a new “local” test - ???– or new theoretical input - ??? – or LUCK
• CMB vs. SN Ia
x=z+1
Maor & Brustein (2003)
Maor et al astro-ph/0112...
Linder, astro-ph/0212...
