j. frieman et al- dark energy

8/3/2019 J. Frieman et al- Dark Energy

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Dark Energy

J. Frieman: Overview 30

A. Kim: Supernovae 30

B. Jain: Weak Lensing 30

M. White: Baryon Acoustic Oscillations 30

P5, SLAC, Feb. 22, 2008


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Progress since last P5 ReportBEPAC recommends JDEM as highest-priority

for NASAs Beyond Einstein program: joint AO

expected 2008DES recommended for CD2/3a approval

LSST successful Conceptual Design Review

ESA Cosmic Visions Program: DUNE, SPACEConcept Advisory Team studying possible

merger


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3

What is causing cosmic acceleration?

Dark Energy:

Gravity:

Key Experimental Questions:

1. Is DE observationally distinguishable from a cosmologicalconstant, for which w =1?

2. Can we distinguish between gravity and dark energy?

Combine distance with structure-growth probes

3. Does dark energy evolve: w=w(z)?

G"= 8#G[T

"(matter)+ T

"(dark energy)]

DE equation of state : w = Tii /T0

0< $1/ 3

G"+ f(g

") = 8#GT

"(matter)


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4

Probe dark energy through the history of the expansion rate:

and the growth of large-scale structure:

Four Primary Probes (DETF):

Weak Lensingcosmic shear Distance r(z)+growth

Supernovae Distance

Baryon Acoustic Oscillations Distance+H(z)

Cluster counting Distance+growth

What is the nature of Dark Energy?

H2 (z)

H02

="m

(1+ z)3+"

DEexp 3 (1+ w(z))dln(1+ z)#[ ] + 1$"m $"DE( ) 1+ z( )

2

"# a( )#

r(z) = Fdz

H z( )"#

$%

&

'(

dV

dzd)=

r2(z)

H(z)


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5

Probe dark energy through the history of the expansion rate:

and the growth of large-scale structure:

Four Primary Probes (DETF):

Weak Lensingcosmic shear Distance r(z)+growth

Supernovae Distance

Baryon Acoustic Oscillations Distance+H(z)

Cluster counting Distance+growth

What is the nature of Dark Energy?

H2 (z)

H02

="m

(1+ z)3+"

DEexp 3 (1+ w(z))dln(1+ z)#[ ] + 1$"m $"DE( ) 1+ z( )

2

"# a( )#

r(z) = Fdz

H z( )"#

$%

&

'(

dV

dzd)=

r2(z)

H(z)


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6

Model Assumptions

Most current data analyses assume a simplified, two-

parameter class of models:

Future experiments aim to constrain (at least) 4-

parameter models:

Higher-dimensional EOS parametrizations possible

Other descriptions possible (e.g., kinematic)

"m,"

DE,w(z) # either : "

m,"

DE(w = $1)

or : "m, w (constant), flat : "

m+"

DE=1

"m,"

DE,w(a)= w

0+ w

a (1# a

)


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7

Current

Constraints onConstantDark

Energy Equation

of State

2-parameter model:

Data consistent with

w=10.1

Allen et al 07

w, "m


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Current

Constraints onConstantDark

Energy Equation

of State

2-parameter model:

Data consistent with

w=10.1

Allen et al 07

Kowalski et al 08

w, "m


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Curvature and Dark Energy

WMAP3+

SDSS+2dF+SN

w(z)=constant

3-parametermodel:

Spergel etal 07

w, "m

, "k


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Much weaker

current

constraints on

Time-varying

Dark Energy

3-parameter model

marginalized overm

Kowalski et al 08 Assumes flat Universe

w(z) = w0 + wa (1" a)+ ...


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Dark Energy Task Force Report (2006)

Defined Figure of Merit to compare expts andmethods:

Highlighted 4 probes: SN, WL, BAO, CL

Envisioned staged program of experiments:

Stage II: on-going or funded as of 2006Stage III: intermediate in scale + time

Stage IV: longer-term, larger scale

LSST, JDEM

FoM" 1

#(w0)#(wa )

"3

"10


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Much weaker

current

constraints on

Time-varying

Dark Energy

3-parameter model

marginalized overm

Kowalski et al 08

w(z) = w0 + wa (1" a)

``Stage III

``Stage IV

Theoretical

prejudice


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Growth of Large-

scale Structure

Robustness of the

paradigm recommends

its use as a Dark

Energy probe

Price:additional

cosmological and

structure formation

parameters

Bonus:additional

structure formation

parameters


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Expansion History vs. Perturbation Growth

Growth ofPerturbations

probesH(z)

and gravitymodifications

Linder


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Expansion History vs. Perturbation Growth

Growth ofPerturbations

probesH(z)

and gravitymodifications

Linder


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Probing Dark Energy

Primary Techniques identified by the

Dark Energy Task Force report:

Supernovae

Galaxy Clusters

Weak Lensing

Baryon Acoustic Oscillations

Multiple Techniques needed: complementary in systematics

and in science reach


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Caveat:

Representative list,

not guaranteed to be

complete or accurate


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Type Ia SN

Peak Brightness

as calibratedStandard Candle

Peak brightness

correlates with

decline rate

Variety of algorithms

for modeling these

correlations

After correction,~ 0.15 mag(~7% distance error)

Lumino

sity

Time


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2007

Wood-Vasey etal 07


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Large-scale Correlations of

SDSS Luminous Red Galaxies

Acoustic series in

P(k) becomes a

single peak in (r)

Pure CDM model

has no peak

Eisenstein, etal

05

Redshift-

space

Correlation

Function

Baryon

Acoustic

Oscillations

seen in

Large-scale

Structure

"(r) =

#(r

x)#(r

x+

r

r)


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Cold Dark

Matter Models

Power Spectrum

of the Mass

Density

" k( ) = d3# x $ eir

k$r

x"%x( )

%

" k1( )" k2( ) =

2#( )3

P k1( )"

3r

k1+

r

k2( )


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22Tegmark etal 06

SDSS


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Weak lensing: shear and mass

Jain


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Cosmic Shear Correlations

Shear

Amplitude

VIRMOS-Descart Survey

Signal

Noise+systematics

2x10-4

10-4

0

,()

0.6Mpc/h 6Mpc/h 30Mpc/h

CDM

55 sq deg

z= 0.8

Van

Waerbeke

etal 05


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Clusters and Dark Energy

MohrVolume Growth

(geometry)

Number of clusters above observable mass threshold

Dark Energy

equation of state

dN(z)

dzd"=

dV

dz d"n z( )

Requirements1.Understand formation of darkmatter halos

2.Cleanly select massive dark matterhalos (galaxy clusters) over a range

of redshifts3.Redshift estimates for each cluster

4.Observable proxy O that can beused as cluster mass estimate:

p(O|M,z)

Primary systematic:

Uncertainty in bias & scatter ofmass-observable relation


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Clusters form hierarchically

z = 7 z = 5 z = 3

z = 1 z = 0.5 z = 0

5 Mpc

dark matterdark matter

timetime

Kravtsov


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Theoretical Abundance of Dark Matter Halos

Warren et al 05

Warren etal

n(z) = (dn /dlnM)dlnMMmin

"

#


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Cluster Selection

4 Techniques for Cluster Selection:

Optical galaxy concentration

Weak Lensing

Sunyaev-Zeldovich effect (SZE)

X-ray

Cross-compare selection to controlsystematic errors


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Photometric Redshifts

Measure relative flux in

multiple filters:

track the 4000 A break

Precision is sufficient

for Dark Energy probes,

providederror distributions

well measured.

Need deep spectroscopic galaxy

samples to calibrate

Redshifted Elliptical galaxy spectrum


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Photometric Redshifts

Measure relative flux in

multiple filters:

track the 4000 A break

Precision is sufficient

for Dark Energy probes,

providederror distributions

well measured.

Need deep spectroscopic galaxy

samples to calibrate

Redshifted Elliptical galaxy spectrum


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Cluster Mass Estimates

4 Techniques for Cluster Mass Estimation:

Optical galaxy concentration

Weak Lensing

Sunyaev-Zeldovich effect (SZE)

X-ray

Cross-compare these techniques to

reduce systematic errors

Additional cross-checks:

shape of mass function; cluster

correlations


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Calibrating the Cluster Mass-

Observable Relation

Weak Lensing by

stacked SDSS Clusters

insensitive toprojection effects

Calibrate mass-

richness

Johnston, Sheldon, etal 07


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Current Constraints: X-ray clusters

Mantz, et al 2007


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Systematic Errors

Supernovae: uncertainties in dust and SN colors;

selection biases; ``hidden luminosity evolution;

limited low-z sample for training & anchoring

BAO: redshift distortions; galaxy bias; non-

linearities; selection biases

Weak Lensing: additive and multiplicative shear

errors; photo-z systematics; small-scale non-linearity

& baryonic efffects

Clusters: scatter & bias in mass-observable relation;

uncertainty in observable selection function; small-

scale non-linearity & baryonic effects


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Conclusions

Excellent prospects for increasing the precision on DarkEnergy parameters from a sequence of increasingly complex

and ambitious experiments over the next 5-15 years

Exploiting complementarity of multiple probes will be key:

we dont know what the ultimate systematic errorfloors for

each method will be. Combine geometric with structure-

growth probes to help distinguish modified gravity from dark

energy.

What parameter precision is needed to stimulate theoretical

progress? It depends in large part on what the answer is.

j. frieman et al- dark energy

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