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Dark Energy: Dark Energy:

Illuminating the DarkIlluminating the Dark

Eric Linder University of California, BerkeleyLawrence Berkeley National Lab

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Discovery! AccelerationDiscovery! Acceleration

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Exploring Dark EnergyExploring Dark Energy

New quantum physics? Does nothing weigh something?

New gravitational physics? Is nowhere somewhere?

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Today’s InflationToday’s Inflation

Map the expansion history precisely and see the transition from acceleration to

deceleration.

Test the cosmology framework – alternative gravitation, higher dimensions, etc.

SNAP constraints

supe

r ac

cele

ratio

n

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Present Day InflationPresent Day Inflation

Map the expansion history precisely and see the transition from acceleration to

deceleration.

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Density History of the UniverseDensity History of the Universe

Map the density history precisely, back to the matter dominated epoch.

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Mapping Our HistoryMapping Our History

The subtle slowing down and speeding up of the expansion, of distances with time: a(t), maps out cosmic history like tree rings map out the Earth’s climate history.

STScI

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Cosmic ArchaeologyCosmic Archaeology

CMB: direct probe of quantum fluctuations

Time: 0.003% of the present age of the universe.

(When you were 0.003% of your present age, you were 2 cells big!)

Supernovae: direct probe of cosmic expansion

Time: 30-100% of present age of universe

(When you were 12-40 years old)

Cosmic matter structures: less direct probes of expansion

Pattern of ripples, clumping in space, growing in time.

3D survey of galaxies and clusters - Lensing.

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The Universe: Early and LateThe Universe: Early and Late

Relic imprints of quantum particle creation in inflation - epoch of acceleration at 10-35 s and energies near the Planck scale (a trillion times higher than in any particle acclerator).

These ripples in energy density also occur in matter, as denser and less dense regions.

Denser regions get a “head start” and eventually form into galaxies and clusters of galaxies. How quickly they grow depends on the expansion rate of the universe.

It’s all connected!

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COBE WMAP

Planck

What do we see in the CMB?What do we see in the CMB?

A view of the universe 99.997% of the way back toward the Big Bang - and much more.

POLARBEAR has 2.5x the resolution and 1/5x the noise

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Geometry of SpaceGeometry of Space

WMAP/NASA/Tegmark

CMB tells us about the geometry of space - flat? curved?

But not much about evolution (snapshot) or dark energy (too early).

Escher

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Type Ia SupernovaeType Ia Supernovae

• Exploding star, briefly as bright as an entire galaxy• Characterized by no Hydrogen, but with Silicon• Gains mass from companion until undergoes thermonuclear runaway

Standard explosion from nuclear physics

Insensitive to initial conditions: “Stellar amnesia”Höflich, Gerardy, Linder, & Marion 2003

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Standardized CandleStandardized Candle

Redshift tells us the expansion factor a

Time after explosion

Bri

ghtn

ess

Brightness tells us distance away (lookback time t)

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Standard CandlesStandard Candles

Brightness tells us distance away (lookback time)

Redshift measured tells us expansion factor (average distance between galaxies)

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Discovering SupernovaeDiscovering Supernovae

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Nearby Supernova Factory

Understanding SupernovaeUnderstanding Supernovae

High z: “Decelerating and Dustfree” HST Cycle 14, 219 orbits

Supernova Properties Astrophysics

G. Aldering (LBL)

Cleanly understood astrophysics leads to cosmology

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Images

Spectra

Redshift & SN Properties

data analysis physics

Nature ofDark Energy

Each supernova is “sending” us a rich stream of information about itself.

What makes SN measurement special?What makes SN measurement special? Control of systematic uncertaintiesControl of systematic uncertainties

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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Current Data: SNLSCurrent Data: SNLS

Supernova Legacy Survey:

Rolling search on CFHT 2003-08; spectra First year results (71 SN), Astier et al. 2006 Expect total of 500-700 SN at z<0.95

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Current Data: SNLSCurrent Data: SNLS

Cosmological Constraints: consistent with CDM

But current data has no leverage on the dynamics, i.e. w. Analyses assume constant w.

Astier et al. 2006 Spergel et al. 2006

2020

Looking Back 10 Billion YearsLooking Back 10 Billion Years

To see the most distant supernovae, we must observe from space.

A Hubble Deep Field has scanned 1/25 millionth of the sky.

This is like meeting 12 people and trying to understand the complexity of the entire US!

STScI

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Looking Back 10 Billion YearsLooking Back 10 Billion Years

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

STScI

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Dark Energy – The Next GenerationDark Energy – The Next Generation

SNAP: Supernova/Acceleration Probe

Dedicated dark energy probe

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Design a Space MissionDesign a Space Mission

colorful

wide

GOODS

HDF

~104 Hubble Deep Field [SN]

plus ~106 HDF [WL]

deepdeep• Redshifts z=0-1.7 • Exploring the last . 10 billion years • 70% of the age of . the universe

Both optical and near infrared wavelengths to see thru dust.

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New TechnologyNew Technology

Half billion pixel array

36 optical CCDs

36 near infrared detectors

New technology LBNL CCDs

Guider

Spectrographport

Visible

NIR

Focus starprojectors

Calibration projectors

JWST Field of View

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Astrophysical UncertaintiesAstrophysical Uncertainties

Systematic Control

Host-galaxy dust extinction

Wavelength-dependent absorption identified with high S/N multi-band photometry.

Supernova evolution Supernova subclassified with high S/N light curves and peak-brightness spectrum.

Flux calibration error Program to construct a set of 1% error flux standard stars.

Malmquist bias Supernova discovered early with high S/N multi-band photometry.

K-correction Construction of a library of supernova spectra.

Gravitational lensing Measure the average flux for a large number of supernovae in each redshift bin.

Non-Type Ia contamination

Classification of each event with a peak-brightness spectrum.

For accurate and precision cosmology, need to identify and control systematic uncertainties.

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Beyond GaussianBeyond Gaussian

Gravitational lensing:

Few hi z SN poor PDF sampling

Flux vs. magnitude bias

Holz & Linder 2004

Extinction bias:

One sided prior biases results

Dust correction crucial; need NIR

Linder & Miquel 2004

No extinction (perfect) Extinction correction

W With AV bias With AV+RV bias

Current data quality

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Controlling SystematicsControlling Systematics

Same SN, Different z Cosmology Same z, Different SN Systematics Control

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Baryon Acoustic OscillationsBaryon Acoustic Oscillations

The same primordial imprints in the photon field show up in matter density fluctuations.

Baryon acoustic oscillations = patterned distribution of galaxies on very large scales (~150 Mpc).

In the beginning... (well, 10-350,000 years after)

It was hot. Normal matter was p+,e- – charged – interacting fervently with photons.

This tightly coupled them, photon mfp << ct, and so they acted like a fluid.

Density perturbations in one would cause perturbations in the other, but gravity was offset by pressure, so they couldn’t grow - merely oscillated.

On the largest scales, set by the sound horizon, the perturbations were preserved.

(CMB)

Galaxy cluster

size

M. White

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- Standard ruler: we know the sound horizon by measuring the CMB; we measure the “wiggle” scale distance

- Like CMB is simple, linear physics – but require large, deep, galaxy redshift surveys (millions of galaxies, thousand(s) of deg2)

- Possibly WFMOS spectral or SNAP photometric survey

- Complementary with SN if dark energy dynamic

Baryon Acoustic OscillationsBaryon Acoustic Oscillations

But...

Observations give nonlinear, galaxy power spectrum in redshift space

Theory predicts linear, matter power spectrum in real space

(Plus selection effects of galaxy markers)

Large scale power: mode coupling Bias

Small scale power: velocity distortions

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SN

factory

SNLS

Baryon Osc.

SNAP

HST

Cluster

SN

Perlmutter

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Growth History of StructureGrowth History of Structure

While dark energy itself does not cluster much, it affects the growth of matter structure.

Fractional density contrast = m/m evolves as

+ 2H = 4Gm

Sourced by gravitational instability of density contrast, suppressed by Hubble drag.

Matter domination case:

~ a-3 ~ t-2, H ~ (2/3t). Try ~ tn.

Characteristic equation n(n-1)+(4/3)n-(3/2)(4/9)=0. Growing mode n=+2/3, i.e.

~ a

.. .

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Gravitational PotentialGravitational Potential

Poisson equation

2(a)=4Ga2 m= 4Gm(0) g(a)

Growth rate of density fluctuations g(a) = (m/m)/a

In matter dominated (hence decelerating) universe, m/m ~ a so g=const and =const.

By measuring the breakdown of matter domination we see the influence of dark energy.

• Direct count of growth - number of clusters vs. z [tough]

• Decay of potentials thru CMB ISW effect [cosmic variance]

• Effect of potentials on light rays - gravitational lensing

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Gravitational LensingGravitational Lensing

Gravity bends light… - we can detect dark matter through its gravity, - objects are magnified and distorted, - we can view “CAT scans” of growth of structure

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Gravitational LensingGravitational Lensing

“Galaxy wallpaper” Lensing by (dark) matter along the line of sight

N. Kaiser

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Gravitational LensingGravitational Lensing

Lensing measures the mass of clusters of galaxies.

By looking at lensing of sources at different distances (times), we measure the growth of mass.

Clusters grow by swallowing more and more galaxies, more mass.

Acceleration - stretching space - shuts off growth, by keeping galaxies apart.

So by measuring the growth history, lensing can detect the level of acceleration, the amount of dark energy.

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Cluster Cluster AbundancesAbundances

Optical: light mass Xray: hot gas gravitational potential mass

Sunyaev-Zel’dovich: hot e- scatter CMB mass

Weak Lensing: gravity distorts images of background galaxies

TraditionalDifficult for z>1Detects light, not massMass of what?

Clean detectionsDifficult for z>1Need optical survey for redshiftDetects flux, not massOnly cluster centerAssumes simple: ~ne

2

Clean detectionsIndepedent of redshiftNeed optical survey for redshiftDetects flux, not massAssumes ~simple: ~neTe

Detect mass directlyCan go to z>1Line of sight contaminationEfficiency reduced

Clusters -- largest bound objects. DE + astrophysics. Uncertainty in mass of 0.1 dex gives wconst~0.1 [M. White], w~?

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Cosmic ToolkitCosmic Toolkit

The Founder: Supernovae Ia distance-redshift The Players on the Field: SN Ia, Weak Lensing

The main challenge will be control of systematics -- clean astrophysics to learn new physics

Geometric Methods – “lightbulb”: a standard; don’t care how filament works (test it) SN Ia, SN II, Weak Lensing[CCC], Baryon Oscillations

Geometry+Mass – “flashlight”: need to know about lens and battery [nonlinear mass distribution] Weak Lensing[structure], Strong Lensing

Geometry+Mass+Gas – “torch”: need to know about the wood, flame, wind [hydrodynamics] SZ Effect, Cluster Counts