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Dark EnergyCurrent theoretical issues and progress toward
future experiments
Andreas Albrecht (UC Davis)
LEPP Journal Club Seminar, Cornell University
December 1 2006
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Cosmic acceleration
Accelerating matter is required to fit current data
Supernova
Preferred by modern data
Amount of “ordinary” gravitating matter A
mount
of
w=
-1 m
att
er
(“D
ark
energ
y”)
“Ordinary” non accelerating matter
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Dark Energy (accelerating)
Dark Matter (Gravitating)
Ordinary Matter (observed in labs)
95% of the cosmic matter/energy is a mystery. It has never been observed even in our best laboratories
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Dark energy appears to be the dominant component of the physical
Universe, yet there is no persuasive theoretical explanation. The
acceleration of the Universe is, along with dark matter, the observed
phenomenon which most directly demonstrates that our fundamental
theories of particles and gravity are either incorrect or incomplete.
Most experts believe that nothing short of a revolution in our
understanding of fundamental physics* will be required to achieve a
full understanding of the cosmic acceleration. For these reasons, the
nature of dark energy ranks among the very most compelling of all
outstanding problems in physical science. These circumstances
demand an ambitious observational program to determine the dark
energy properties as well as possible.
From the Dark Energy Task Force report (2006)www.nsf.gov/mps/ast/detf.jsp,
astro-ph/0690591*My emphasis
![Page 5: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/5.jpg)
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Dark energy appears to be the dominant component of the physical
Universe, yet there is no persuasive theoretical explanation. The
acceleration of the Universe is, along with dark matter, the observed
phenomenon which most directly demonstrates that our fundamental
theories of particles and gravity are either incorrect or incomplete.
Most experts believe that nothing short of a revolution in our
understanding of fundamental physics* will be required to achieve a
full understanding of the cosmic acceleration. For these reasons, the
nature of dark energy ranks among the very most compelling of all
outstanding problems in physical science. These circumstances
demand an ambitious observational program to determine the dark
energy properties as well as possible.
From the Dark Energy Task Force report (2006)www.nsf.gov/mps/ast/detf.jsp,
astro-ph/0690591*My emphasis
DETF = a HEPAP/AAAC subpanel to guide planning of future dark energy experiments
![Page 6: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/6.jpg)
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Dark energy appears to be the dominant component of the physical
Universe, yet there is no persuasive theoretical explanation. The
acceleration of the Universe is, along with dark matter, the observed
phenomenon which most directly demonstrates that our fundamental
theories of particles and gravity are either incorrect or incomplete.
Most experts believe that nothing short of a revolution in our
understanding of fundamental physics* will be required to achieve a
full understanding of the cosmic acceleration. For these reasons, the
nature of dark energy ranks among the very most compelling of all
outstanding problems in physical science. These circumstances
demand an ambitious observational program to determine the dark
energy properties as well as possible.
From the Dark Energy Task Force report (2006)www.nsf.gov/mps/ast/detf.jsp,
astro-ph/0690591*My emphasis
DETF = a HEPAP/AAAC subpanel to guide planning of future dark energy experiments
More info here
![Page 7: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/7.jpg)
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This talk
Part 1:
A few attempts to explain dark energy
- Motivations, Problems and other comments
Theme: We may not know where this revolution is taking us, but it is already underway:
(see e.g. Copeland et al 2006 review)
Part 2
Planning new experiments
(see e.g. DETF report and AA & Bernstein 2006)
![Page 8: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/8.jpg)
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This talk
Part 1:
A few attempts to explain dark energy
- Motivations, Problems and other comments
Theme: We may not know where this revolution is taking us, but it is already underway:
(see e.g. Copeland et al 2006 review)
Part 2
Planning new experiments
(see e.g. DETF report and AA & Bernstein 2006)
![Page 9: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/9.jpg)
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This talk
Part 1:
A few attempts to explain dark energy
- Motivations, Problems and other comments
Theme: We may not know where this revolution is taking us, but it is already underway:
(see e.g. Copeland et al 2006 review)
Part 2
Planning new experiments
(see e.g. DETF report and AA & Bernstein 2006)
![Page 10: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/10.jpg)
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Some general issues:
Properties:
Solve GR for the scale factor a of the Universe (a=1 today):
Positive acceleration clearly requires
• (unlike any known constituent of the Universe) or
• a non-zero cosmological constant or
• an alteration to General Relativity.
/ 1/ 3w p
43
3 3
a Gp
a
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• Today,
• Many field models require a particle mass of
Some general issues:
Numbers:
4120 4 310 10DE PM eV
31010Qm eV H 2 2
Q P DEm M from
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• Today,
• Many field models require a particle mass of
Some general issues:
Numbers:
4120 4 310 10DE PM eV
31010Qm eV H 2 2
Q P DEm M from
Where do these come from and how are they protected from quantum corrections?
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
Vacuum energy problem (we’ve gotten “nowhere” with this)
= 10120
0 ?
Vacuum Fluctuations
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
Vacuum energy problem (we’ve gotten “nowhere” with this)
= 10120
0 ?
Vacuum Fluctuations
See e.g. Tye & Wasserman, Csaki et al Flannagan et al (Braneworld)
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
The string theory landscape (a radically different idea of what we mean by a fundamental theory)
KKLT, Tye etc
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
The string theory landscape (a radically different idea of what we mean by a fundamental theory)
“Theory of Everything”
“Theory of Anything”
?
KKLT, Tye etc
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
The string theory landscape (a radically different idea of what we mean by a fundamental theory)
Not exactly a cosmological
constant
KKLT, Tye etc
![Page 18: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/18.jpg)
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
De Sitter limit: Horizon Finite Entropy
Banks, Fischler, Susskind, AA & Sorbo etc
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2 1S A H
“De Sitter Space: The ultimate equilibrium for the universe?
Horizon
Quantum effects: Hawking Temperature
8
3 DE
GT H
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2 1S A H
“De Sitter Space: The ultimate equilibrium for the universe?
Horizon
Quantum effects: Hawking Temperature
8
3 DE
GT H
Does this imply (via “ “)
a finite Hilbert space for physics?
lnS N
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
De Sitter limit: Horizon Finite Entropy Equilibrium Cosmology
Rare Fluctuation
Banks, Fischler, Susskind, AA & Sorbo etc
![Page 22: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/22.jpg)
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
De Sitter limit: Horizon Finite Entropy Equilibrium Cosmology
Rare Fluctuation
Banks, Fischler, Susskind, AA & Sorbo etc
“Boltzmann’s Brain” ?
![Page 23: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/23.jpg)
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Specific ideas: i) A cosmological constant
• Nice “textbook” solutions BUT
• Deep problems/impacts re fundamental physics
is not the “simple option”
![Page 24: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/24.jpg)
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Some general issues:
Alternative Explanations?:
Is there a less dramatic explanation of the data?
For example is supernova dimming due to
• dust? (Aguirre)
• γ-axion interactions? (Csaki et al)
• Evolution of SN properties? (Drell et al)
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Some general issues:
Alternative Explanations?:
Is there a less dramatic explanation of the data?
For example is supernova dimming due to
• dust? (Aguirre)
• γ-axion interactions? (Csaki et al)
• Evolution of SN properties? (Drell et al)
Many of these are under increasing pressure from data, but such skepticism is critically important.
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• Recycle inflation ideas (resurrect dream?)
• Serious unresolved problems
Explaining/ protecting
5th force problem
Vacuum energy problem
What is the Q field? (inherited from inflation)
Why now? (Often not a separate problem)
Specific ideas: ii) A scalar field (“Quintessence”)
31010Qm eV H
0
![Page 27: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/27.jpg)
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Quintessence: Model the dark energy by a homogeneous scalar field obeying
3 0dV
Hd
With 2
2V
and 2
2p V
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today (t=14.5 Gyr). (not some other time)
Why now? (Often not a separate problem)
10-20
100-0.5
0
0.5
1
a
rad
matter
DE
i ii
c tot
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Specific ideas: ii) A scalar field (“Quintessence”)
• Illustration: Pseudo Nambu Goldstone Boson (PNGB) models
1)/cos(4 fMV
With f 1018GeV, M 10-3eV
PNGB: Frieman, Hill, Stebbins, & Waga 1995
PNGB mechanism protects M and 5th force issues
![Page 30: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/30.jpg)
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Specific ideas: ii) A scalar field (“Quintessence”)
• Illustration: Pseudo Nambu Goldstone Boson (PNGB) models
0123-1.5
-1
-0.5
0
0.5
1
z
,
w
r
m
D
w
Hall et al 05
![Page 31: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/31.jpg)
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Dark energy and the ego test
![Page 32: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/32.jpg)
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Specific ideas: ii) A scalar field (“Quintessence”)
• Illustration: Exponential with prefactor (EwP) models:
All parameters O(1) in Planck units,
motivations/protections from extra dimensions & quantum gravity
2
0( ) exp /V V B A
AA & Skordis 1999
Burgess & collaborators
(e.g. ) 34B .005A 8 0 1V
![Page 33: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/33.jpg)
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Specific ideas: ii) A scalar field (“Quintessence”)
• Illustration: Exponential with prefactor (EwP) models:
All parameters O(1) in Planck units,
motivations/protections from extra dimensions & quantum gravity
2
0( ) exp /V V B A
AA & Skordis 1999
Burgess & collaborators
(e.g. ) 34B .005A 8 0 1V
V
AA & Skordis 1999
![Page 34: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/34.jpg)
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Specific ideas: ii) A scalar field (“Quintessence”)
• Illustration: Exponential with prefactor (EwP) models:
All parameters O(1) in Planck units,
motivations/protections from extra dimensions & quantum gravity
2
0( ) exp /V V B A
AA & Skordis 1999
Burgess & collaborators
(e.g. ) 34B .005A 8 0 1V
V
AA & Skordis 1999
See also R. Bean
![Page 35: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/35.jpg)
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Specific ideas: ii) A scalar field (“Quintessence”)
• Illustration: Exponential with prefactor (EwP) models:
AA & Skordis 199910
-2010
0-1.5
-1
-0.5
0
0.5
1
a
,
w
r
m
D
w
![Page 36: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/36.jpg)
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Specific ideas: iii) A mass varying neutrinos (“MaVaNs”)
• Exploit
• Issues Origin of “acceleron” (varies neutrino mass, accelerates the universe)
gravitational collapse
1/ 4 310DEm eV
Faradon, Nelson & Weiner
Afshordi et al 2005
Spitzer 2006
![Page 37: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/37.jpg)
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Specific ideas: iii) A mass varying neutrinos (“MaVaNs”)
• Exploit
• Issues Origin of “acceleron” (varies neutrino mass, accelerates the universe)
gravitational collapse
1/ 4 310DEm eV
Faradon, Nelson & Weiner
Afshordi et al 2005
Spitzer 2006
“ ”
![Page 38: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/38.jpg)
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Specific ideas: iv) Modify Gravity
• Not something to be done lightly, but given our confusion about cosmic acceleration, well worth considering.
• Many deep technical issues
See e.g. Bean et al
e.g. DGP (Dvali, Gabadadze and Porrati)
Charmousis et alGhosts
![Page 39: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/39.jpg)
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This talk
Part 1:
A few attempts to explain dark energy
- Motivations, Problems and other comments
Theme: We may not know where this revolution is taking us, but it is already underway:
(see e.g. Copeland et al 2006 review)
Part 2
Planning new experiments
(see e.g. DETF report and AA & Bernstein 2006)
![Page 40: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/40.jpg)
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This talk
Part 1:
A few attempts to explain dark energy
- Motivations, Problems and other comments
Theme: We may not know where this revolution is taking us, but it is already underway:
(see e.g. Copeland et al 2006 review)
Part 2
Planning new experiments
(see e.g. DETF report and AA & Bernstein 2006)
![Page 41: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/41.jpg)
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Astronomy Primer for Dark EnergyAstronomy Primer for Dark EnergyAstronomy Primer for Dark EnergyAstronomy Primer for Dark EnergySolve GR for the scale factor a of the Universe (a=1 today):
Positive acceleration clearly requires unlike any knownconstituent of the Universe, or a non-zero cosmological constant - or an alteration to General Relativity.
2
2
8
3 3NGa k
a a
The second basic equation is
Today we have2
2 00
8
3 3NGa
H ka
/ 1/ 3w p
From DETF
![Page 42: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/42.jpg)
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Hubble ParameterHubble Parameter
18GN0
3H02
3H0
2 k
H02 k
We can rewrite this as
To get the generalization that applies not just now (a=1), we needto distinguish between non-relativistic matter and relativistic matter.We also generalize to dark energy with a constant w, not necessarily equal to -1:
Dark Energy
curvature
rel. matter
non-rel. matter
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What are the observable quantities?What are the observable quantities?Expansion factor a is directly observed by redshifting of emitted photons: a=1/(1+z), z is “redshift.”
Time is not a direct observable (for present discussion). A measure of elapsed time is the distance traversed by an emitted photon:
This distance-redshift relation is one of the diagnostics of dark energy. Given a value for curvature, there is 1-1 map between D(z) and w(a).
Distance is manifested by changes in flux, subtended angle, and sky densities of objects at fixed luminosity, proper size, and space density.
These are one class of observable quantities for dark-energy study.
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Another observable quantity:Another observable quantity:The progress of gravitational collapse is damped by expansion of the Universe. Density fluctuations arising from inflation-era quantum fluctuations increase their amplitude with time. Quantify this by the growth factor g of density fluctuations in linear perturbation theory. GR gives:
This growth-redshift relation is the second diagnostic of dark energy. If GR is correct, there is 1-1 map between D(z) and g(z).
If GR is incorrect, observed quantities may fail to obey this relation.
Growth factor is determined by measuring the density fluctuations in nearby dark matter (!), comparing to those seen at z=1088 by WMAP.
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What are the observable quantities?What are the observable quantities?
Future dark-energy experiments will require percent-level precision onthe primary observables D(z) and g(z).
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Dark Energy with Type Ia SupernovaeDark Energy with Type Ia Supernovae
• Exploding white dwarf stars: mass exceeds Chandrasekhar limit.
• If luminosity is fixed, received flux gives relative distance via Qf=L/4D2.
• SNIa are not homogeneous events. Are all luminosity-affecting variables manifested in observed properties of the explosion (light curves, spectra)? Supernovae Detected in HST
GOODS Survey (Riess et al)
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Dark Energy with Type Ia SupernovaeDark Energy with Type Ia Supernovae
Example of SN data: HST GOODS Survey (Riess et
al)
Clear evidence of acceleration!
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Riess et al astro-ph/0611572
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Dark Energy with Baryon Acoustic OscillationsDark Energy with Baryon Acoustic Oscillations
•Acoustic waves propagate in the baryon-photon plasma starting at end of inflation.
•When plasma combines to neutral hydrogen, sound propagation ends.
•Cosmic expansion sets up a predictable standing wave pattern on scales of the Hubble length. The Hubble length (~sound horizon rs) ~140 Mpc is imprinted on the matter density pattern.
•Identify the angular scale subtending rs then use s=rs/D(z)
•WMAP/Planck determine rs and the distance to z=1088.
•Survey of galaxies (as signposts for dark matter) recover D(z), H(z) at 0<z<5.
•Galaxy survey can be visible/NIR or 21-cm emission
BAO seen in CMB(WMAP)
BAO seen in SDSSGalaxy correlations
(Eisenstein et al)
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Dark Energy with Galaxy ClustersDark Energy with Galaxy Clusters•Galaxy clusters are the largest structures in Universe to undergo gravitational collapse.
•Markers for locations with density contrast above a critical value.
•Theory predicts the mass function dN/dMdV. We observe dN/dzd.
•Dark energy sensitivity:
•Mass function is very sensitive to M; very sensitive to g(z).
•Also very sensitive to mis-estimation of mass, which is not directly observed.
Optical View(Lupton/SDSS)
Cluster method probes both D(z) and g(z)
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Dark Energy with Galaxy ClustersDark Energy with Galaxy Clusters
30 GHz View(Carlstrom et al)
Sunyaev-Zeldovich effect
X-ray View(Chandra)
Optical View(Lupton/SDSS)
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Galaxy Clusters from ROSAT X-ray surveysGalaxy Clusters from ROSAT X-ray surveys
ROSAT cluster surveys yielded ~few 100 clusters in controlled samples.
Future X-ray, SZ, lensing surveys project few x 10,000 detections.
From Rosati et al, 1999:
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Dark Energy with Weak Gravitational LensingDark Energy with Weak Gravitational Lensing
•Mass concentrations in the Universe deflect photons from distant sources.
•Displacement of background images is unobservable, but their distortion (shear) is measurable.
•Extent of distortion depends upon size of mass concentrations and relative distances.
•Depth information from redshifts. Obtaining 108 redshifts from optical spectroscopy is infeasible. “photometric” redshifts instead.
Lensing method probes both D(z) and g(z)
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Dark Energy with Weak Gravitational LensingDark Energy with Weak Gravitational Lensing
In weak lensing, shapes of galaxies are measured. Dominant noise source is the (random) intrinsic shape of galaxies. Large-N statistics extract lensing influence from intrinsic noise.
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Choose your background photon source:Choose your background photon source:
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Faint background galaxies:
Use visible/NIR imaging to determine shapes.
Photometric redshifts.
Photons from the CMB:
Use mm-wave high-resolution imaging of CMB.
All sources at z=1088.
21-cm photons:
Use the proposed Square Kilometer Array (SKA).
Sources are neutral H in regular galaxies at z<2, or the neutral Universe at z>6.
(lensing not yet detected)
(lensing not yet detected)
Hoekstra et al 2006:
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Q: Given that we know so little about the cosmic acceleration, how do we represent source of this acceleration when we forecast the impact of future experiments?
Consensus Answer: (DETF, Joint Dark Energy Mission
Science Definition Team JDEM STD)
• Model dark energy as homogeneous fluid all information contained in
• Model possible breakdown of GR by inconsistent determination of w(a) by different methods.
/w a p a a
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Q: Given that we know so little about the cosmic acceleration, how do we represent source of this acceleration when we forecast the impact of future experiments?
Consensus Answer: (DETF, Joint Dark Energy Mission
Science Definition Team JDEM STD)
• Model dark energy as homogeneous fluid all information contained in
• Model possible breakdown of GR by inconsistent determination of w(a) by different methods.
/w a p a a
Also: Std cosmological parameters including curvature
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59w
wa
w(a) = w0 + wa(1-a)w(a) = w0 + wa(1-a)
DETF figure of merit:Area
95% CL contour
(DETF parameterization… Linder)
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The DETF stages (data models constructed for each one)
Stage 2: Underway
Stage 3: Medium size/term projects
Stage 4: Large longer term projects (ie JDEM, LST)
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Combination
Technique #2
Technique #1
A technical point: The role of correlations
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DETF Projections
Stage 3
Fig
ure
of m
erit
Impr
ovem
ent
over
S
tage
2
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DETF Projections
Ground
Fig
ure
of m
erit
Impr
ovem
ent
over
S
tage
2
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DETF Projections
Space
Fig
ure
of m
erit
Impr
ovem
ent
over
S
tage
2
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DETF Projections
Ground + Space
Fig
ure
of m
erit
Impr
ovem
ent
over
S
tage
2
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Combination
Technique #2
Technique #1
A technical point: The role of correlations
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From the DETF Executive Summary
One of our main findings is that no single technique can answer the outstanding questions about dark energy: combinations of at least two of these techniques must be used to fully realize the promise of future observations.
Already there are proposals for major, long-term (Stage IV) projects incorporating these techniques that have the promise of increasing our figure of merit by a factor of ten beyond the level it will reach with the conclusion of current experiments. What is urgently needed is a commitment to fund a program comprised of a selection of these projects. The selection should be made on the basis of critical evaluations of their costs, benefits, and risks.
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From the Executive Summary
Success in reaching our ultimate goal will depend on the development of dark-energy science. This is in its infancy. Smaller, faster programs (Stage III) are needed to provide the experience on which the long-term projects can build. These projects can reduce systematic uncertainties that could otherwise impede the larger projects, and at the same time make important advances in our knowledge of dark energy.
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0 0.5 1 1.5 2 2.5-4
-2
0
wSample w(z) curves in w
0-w
a space
0 0.5 1 1.5 2
-1
0
1
w
Sample w(z) curves for the PNGB models
0 0.5 1 1.5 2
-1
0
1
z
w
Sample w(z) curves for the EwP models
w0-wa can only do these
DE models can do this (and much more)
w
z
0( ) 1aw a w w a
How good is the w(a) ansatz?
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0 0.5 1 1.5 2 2.5-4
-2
0
wSample w(z) curves in w
0-w
a space
0 0.5 1 1.5 2
-1
0
1
w
Sample w(z) curves for the PNGB models
0 0.5 1 1.5 2
-1
0
1
z
w
Sample w(z) curves for the EwP models
w0-wa can only do these
DE models can do this (and much more)
w
z
0( ) 1aw a w w a
How good is the w(a) ansatz?
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0 0.5 1 1.5 2 2.5-4
-2
0
wSample w(z) curves in w
0-w
a space
0 0.5 1 1.5 2
-1
0
1
w
Sample w(z) curves for the PNGB models
0 0.5 1 1.5 2
-1
0
1
z
w
Sample w(z) curves for the EwP models
w0-wa can only do these
DE models can do this (and much more)
w
z
How good is the w(a) ansatz?
NB: Better than
0( ) 1aw a w w a
0( )w a w
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10-2
10-1
100
101
-1
0
1
z
Try 9D stepwise constant w(a)
w a
AA & G Bernstein 2006 (astro-ph/0608269 ). More detailed info can be found at http://www.physics.ucdavis.edu/Cosmology/albrecht/MoreInfo0608269/
9 parameters are coefficients of the “top hat functions”
9
11
( ) 1 1 ,i i ii
w a w a wT a a
1,i iT a a
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10-2
10-1
100
101
-1
0
1
z
Try 9D stepwise constant w(a)
w a
AA & G Bernstein 2006
9 parameters are coefficients of the “top hat functions”
9
11
( ) 1 1 ,i i ii
w a w a wT a a
1,i iT a a
Allows greater variety of w(a) behavior
Allows each experiment to “put its best foot forward”
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10-2
10-1
100
101
-1
0
1
z
Try 9D stepwise constant w(a)
w a
AA & G Bernstein 2006
9 parameters are coefficients of the “top hat functions”
9
11
( ) 1 1 ,i i ii
w a w a wT a a
1,i iT a a
Allows greater variety of w(a) behavior
Allows each experiment to “put its best foot forward”
“Convergence”
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Q: How do you describe error ellipsis in 9D space?
A: In terms of 9 principle axes and corresponding 9 errors :
2D illustration:
1
2
Axis 1
Axis 2
if
i
1f
2f
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Q: How do you describe error ellipsis in 9D space?
A: In terms of 9 principle axes and corresponding 9 errors :
2D illustration:
1
2
Axis 1
Axis 2
if
i
1f
2f Assuming Gaussian
distributions for this discussion
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Q: How do you describe error ellipsis in 9D space?
A: In terms of 9 principle axes and corresponding 9 errors :
2D illustration:
1
2
Axis 1
Axis 2
if
i
1f
2f
NB: in general the s form a complete basis:
i ii
w f
if
The are independently measured qualities with errors
i
i
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1 2 3 4 5 6 7 8 90
1
2
Stage 2 ; lin-a NGrid
= 9, zmax
= 4, Tag = 044301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
4
5
6
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
7
8
9
i
Prin
cipl
e A
xes
if i
a
Characterizing 9D ellipses by principle axes and corresponding errorsDETF stage 2
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1 2 3 4 5 6 7 8 90
1
2
Stage 4 Space WL Opt; lin-a NGrid
= 9, zmax
= 4, Tag = 044301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9
i
Prin
cipl
e A
xes
if i
a
Characterizing 9D ellipses by principle axes and corresponding errorsWL Stage 4 Opt
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0 2 4 6 8 10 12 14 16 180
1
2
Stage 4 Space WL Opt; lin-a NGrid
= 16, zmax
= 4, Tag = 054301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9
i
Prin
cipl
e A
xes
if i
a
Characterizing 9D ellipses by principle axes and corresponding errorsWL Stage 4 Opt
“Convergence”
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DETF Figure of Merit:
DETF1 2
1
F
9D Figure of Merit:
9D 9
1
1
ii
F If we set 1i 1i
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BAOp BAOs SNp SNs WLp ALLp1
10
100
1e3
1e4
Stage 3
Bska Blst Slst Wska Wlst Aska Alst1
10
100
1e3
1e4
Stage 4 Ground
BAO SN WL S+W S+W+B1
10
100
1e3
1e4
Stage 4 Space
Grid Linear in a zmax = 4 scale: 0
1
10
100
1e3
1e4
Stage 4 Ground+Space
[SSBlstW lst] [BSSlstW lst] Alllst [SSWSBIIIs] SsW lst
DETF(-CL)
9D (-CL)
DETF/9DF
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BAOp BAOs SNp SNs WLp ALLp1
10
100
1e3
1e4
Stage 3
Bska Blst Slst Wska Wlst Aska Alst1
10
100
1e3
1e4
Stage 4 Ground
BAO SN WL S+W S+W+B1
10
100
1e3
1e4
Stage 4 Space
Grid Linear in a zmax = 4 scale: 0
1
10
100
1e3
1e4
Stage 4 Ground+Space
[SSBlstW lst] [BSSlstW lst] Alllst [SSWSBIIIs] SsW lst
DETF(-CL)
9D (-CL)
DETF/9DF
Stage 2 Stage 4 = 3 orders of magnitude (vs 1 for DETF)
Stage 2 Stage 3 = 1 order of magnitude (vs 0.5 for DETF)
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Define the “scale to 2D” function
2/2D
eDS F F
The idea: Construct an effective 2D FoM by assuming two dimensions with “average” errors (~geometric mean of 9D errors)
Purpose: Separate out the impact of higher dimensions on comparisons with DETF, vs other information from the D9 space (such relative comparisons of data model).
2D 2
1
aveS F
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Bp Bs Sp Ss Wp ALLp
1
23
5 10 20
Stage 3
1
23
5 10 20
Stage 4 Ground
Bska
BLST
Slst
Wska
Wlst
Aska
Alst
B S W SW SWB
1
23
5 10 20
Stage 4 Space
1
23
5 10 20
Stage 4 Ground+Space
[SSB
lstW
lst] [B
SS
lstW
lst] All
lst [S
SW
SB
IIIs] S
sW
lst
DETF(-CL)
9D (-CL)-Scaled to 2D
De= 4 for Stage 4 Pes, ; De= 4.5 for Stage 4 Opt,
De=3 for Stage 3De=2.5 for Stage 2
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Discussion of cost/benefit analysis should take place in higher dimensions (vs current standards)
“form” Frieman’s talk
1
2
Axis 1
Axis 2
1f
2f
DETF
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An example of the power of the principle component analysis:
Q: I’ve heard the claim that the DETF FoM is unfair to BAO, because w0-wa does not describe the high-z behavior which to which BAO is particularly sensitive. Why does this not show up in the 9D analysis?
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BAOp BAOs SNp SNs WLp ALLp1
10
100
1e3
1e4
Stage 3
Bska Blst Slst Wska Wlst Aska Alst1
10
100
1e3
1e4
Stage 4 Ground
BAO SN WL S+W S+W+B1
10
100
1e3
1e4
Stage 4 Space
Grid Linear in a zmax = 4 scale: 0
1
10
100
1e3
1e4
Stage 4 Ground+Space
[SSBlstW lst] [BSSlstW lst] Alllst [SSWSBIIIs] SsW lst
DETF(-CL)
9D (-CL)
DETF/9DF
Specific Case:
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89
1 2 3 4 5 6 7 8 90
1
2
Stage 4 Space BAO Opt; lin-a NGrid
= 9, zmax
= 4, Tag = 044301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9
BAO
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90
1 2 3 4 5 6 7 8 90
1
2
Stage 4 Space SN Opt; lin-a NGrid
= 9, zmax
= 4, Tag = 044301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9
SN
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91
1 2 3 4 5 6 7 8 90
1
2
Stage 4 Space BAO Opt; lin-a NGrid
= 9, zmax
= 4, Tag = 044301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9
BAODETF 1 2,
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92
SN
1 2 3 4 5 6 7 8 90
1
2
Stage 4 Space SN Opt; lin-a NGrid
= 9, zmax
= 4, Tag = 044301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9
1 2,
![Page 93: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/93.jpg)
93
1 2 3 4 5 6 7 8 90
1
2
Stage 4 Space SN Opt; lin-a NGrid
= 9, zmax
= 4, Tag = 044301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9
SNw0-wa analysis shows two parameters measured on average as well as 3.5 of these
2/9
1 21
3.5eD
i
DETF
9D
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94
Upshot of 9D FoM:
1) DETF underestimates impact of expts
2) DETF underestimates relative value of Stage 4 vs Stage 3
3) The above can be understood approximately in terms of a simple rescaling
4) DETF FoM is fine for most purposes (ranking, value of combinations etc).
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95
Dark energy appears to be the dominant component of the physical
Universe, yet there is no persuasive theoretical explanation. The
acceleration of the Universe is, along with dark matter, the observed
phenomenon which most directly demonstrates that our
fundamental theories of particles and gravity are either incorrect or
incomplete. Most experts believe that nothing short of a revolution
in our understanding of fundamental physics will be required to
achieve a full understanding of the cosmic acceleration. For these
reasons, the nature of dark energy ranks among the very most
compelling of all outstanding problems in physical science. These
circumstances demand an ambitious observational program to
determine the dark energy properties as well as possible.
From the Dark Energy Task Force report (2006)www.nsf.gov/mps/ast/detf.jsp
& to appear on the arXiv.
![Page 96: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/96.jpg)
96
Dark energy appears to be the dominant component of the physical
Universe, yet there is no persuasive theoretical explanation. The
acceleration of the Universe is, along with dark matter, the observed
phenomenon which most directly demonstrates that our
fundamental theories of particles and gravity are either incorrect or
incomplete. Most experts believe that nothing short of a revolution
in our understanding of fundamental physics will be required to
achieve a full understanding of the cosmic acceleration. For these
reasons, the nature of dark energy ranks among the very most
compelling of all outstanding problems in physical science. These
circumstances demand an ambitious observational program to
determine the dark energy properties as well as possible.
From the Dark Energy Task Force report (2006)www.nsf.gov/mps/ast/detf.jsp
& to appear on the arXiv.
![Page 97: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/97.jpg)
97
Dark energy appears to be the dominant component of the physical
Universe, yet there is no persuasive theoretical explanation. The
acceleration of the Universe is, along with dark matter, the observed
phenomenon which most directly demonstrates that our
fundamental theories of particles and gravity are either incorrect or
incomplete. Most experts believe that nothing short of a revolution
in our understanding of fundamental physics will be required to
achieve a full understanding of the cosmic acceleration. For these
reasons, the nature of dark energy ranks among the very most
compelling of all outstanding problems in physical science. These
circumstances demand an ambitious observational program to
determine the dark energy properties as well as possible.
From the Dark Energy Task Force report (2006)www.nsf.gov/mps/ast/detf.jsp
& to appear on the arXiv.
![Page 98: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/98.jpg)
98
END
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99
Extra material
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1000 100 200 300 400 500 600
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
sigMax = 4 sigMin = 0 OneModel = 0 OneVersionP1 = 0 OneRun = 0 EigenSR14 AllSolsV22
mode 1
mode 2
Markers label different scalar field models
Coordinates are first three
in
![Page 101: 1 Dark Energy Current theoretical issues and progress toward future experiments Andreas Albrecht (UC Davis) LEPP Journal Club Seminar, Cornell University](https://reader035.vdocument.in/reader035/viewer/2022081519/56649d575503460f94a36bf4/html5/thumbnails/101.jpg)
1010 100 200 300 400 500 600
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
sigMax = 4 sigMin = 0 OneModel = 0 OneVersionP1 = 0 OneRun = 0 EigenSR14 AllSolsV22
mode 1
mode 2
Markers label different scalar field models
Coordinates are first three
in
Implication: New experiments will have very significant discriminating power among actual scalar field models. (See Augusta Abrahamse, Michael Barnard, Brandon Bozek & AA, to appear soon)
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102
1 2 3 4 5 6 7 8 90
1
2
Stage 4 Space WL Opt; lin-a NGrid
= 9, zmax
= 4, Tag = 044301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9
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103
0 2 4 6 8 10 12 14 16 180
1
2
Stage 4 Space WL Opt; lin-a NGrid
= 16, zmax
= 4, Tag = 054301
i
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
0
1
f's
a
1
2
3
4
5
6
7
8
9