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Eric Linder University of California, BerkeleyLawrence Berkeley National Lab

Course on Dark EnergyCourse on Dark Energy Cosmology at the Beach 2009Cosmology at the Beach 2009

JDEM constraints

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OutlineOutline

Lecture 1: Dark Energy in Space

The panoply of observations

Lecture 2: Dark Energy in Theory

The garden of models

Lecture 3: Dark Energy in your Computer

The array of tools – Don’t try this at home!

33

Describing Our UniverseDescribing Our Universe

STScI

95% of the universe is unknown!

New Stuff Old New

Stuff

Us

Us

Had I been present at the creation of the world, I should have recommended something simpler. - Alfonso X ‘The Wise’, King of Castile and Leon

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Mapping HistoryMapping History

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AccelerationAcceleration

Acceleration has:

- Direct (kinematic) effect on spacetime through a(t)

- Dynamic effects on objects within spacetime, e.g. growth, ISW

What appears in the metric is the cosmic scale factor a(t).

The metric can be spatially flat (k=0) but the spacetime is curved if

This is exactly the Equivalence Principle: Gravity = Curvature = Acceleration

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Windows on Dark EnergyWindows on Dark Energy

Light signals travel on null geodesics (ds=0) and measure dt/a = dz/H. Distances are directly affected by acceleration.

Growth, ISW, abundances measure competition between acceleration and gravitational attraction. ISW (decaying potentials) is direct measure of violation of matter domination, not acceleration.

Stretching space suppresses growth. Recall Jeans instability gives exponential growth – expanding space reduces this to power law. Friction term ~ (3-q).

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Dark Energy – the Easy Way?Dark Energy – the Easy Way?

Direct detection? (Dark energy in solar system = 3 hours of sunlight).

Co-dependence? Variations of fundamental constants; lab/accelerator/universe

Direct acceleration? Redshift drift (Sandage 1962; McVittie 1962; Linder 1991,1997)

dz=10-8 over 100 yearsRedshifts are changes in scale/position (“velocities”):

z=[a(t0)-a(te)]/a(te) H0 (t0-te)

Redshift shifts are changes in changes (“acceleration”):

dz/dt0 = [a0-ae]/ae = H0(1+z)-H(z) -zq0H0 t. .

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Cosmic ArchaeologyCosmic Archaeology

CMB: direct probe of quantum fluctuations

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

Supernovae: direct probe of cosmic expansion

Time: 30-100% of present age of universe

3D surveys of galaxies and clusters: probes of expansion + growth

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

BAO, Lensing, Matter power spectrum.

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BREAKBREAK

CMB

1010

COBE WMAP

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.

Planck“GroundPol” has 2.5x the resolution and 1/5x the noise

1111

CMB and Dark EnergyCMB and Dark Energy

CMB provides a lever to break degeneracies

CMB provides a key window on microphysics of dark energy - spatial fluctuations and sound speed cs

2

CMB Polarization (B-mode) is dominated at small angles by high redshift lensing - hence high z structure formation.

Polarization lensing “focuses” on the universe at z=1-4, giving a window on early dark energy, and neutrinos.

See poster by Roland de Putter and 0901.0916

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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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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 physicsInsensitive to initial conditions: “Stellar amnesia”

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Type Ia SupernovaeType Ia Supernovae

Redshift tells us the expansion factor a

Time after explosion

Brig

htne

ss

Brightness tells us distance away (lookback time t)

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Standardized CandlesStandardized Candles

Supernova Legacy Survey (SNLS)

Conley et al 2006

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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Nearby Supernova Factory

Understanding SupernovaeUnderstanding Supernovae

Supernova Properties Astrophysics

G. Aldering (LBL)

Cleanly understood astrophysics leads to cosmology (and astrophysics!)

400 SN Ia with spectra, z=0.03-0.08 >3000 spectra of SN Ia

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Current Data: WorldCurrent Data: World

Union SN Set• Complete reanalysis, refitting of 13 SN data sets

• 396 SNe Ia (58+249) - new low z SN

• Fit Mi between sets and between low-high z

• Study of set by set deviations (residuals, color)

• Blind cosmology analysis!

• Systematic errors ≈ statistical errors

Kowalski et al., ApJ 2008 [arXiv:0804.4142]

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Tests for Systematics and Evolution

No significant deviations from mean of Hubble diagram, or (mostly) in residual slope.

Also no evolution seen in redshift or population tests.

Kowalski et al. 2008, ApJ 2008 [arXiv:0804.4142]

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Current Data: SNLSCurrent Data: SNLS

~310 confirmed SN Ia, 50-60 to be processed

Preliminary ~240 SNSullivan et al 2008

On track for ~500 total 3y data paper ~ early ’09

2020

Imminent ResultsImminent Results

SDSS SN: z=0.1-0.4, 99 SN for Y1 release [498]

Essence: z=0.2-0.7, Y6 release 156 SN

CSP: followup 21 [100+100], I-band Hubble diagram

Local SN studies: KAIT, CfA, PTF, SkyMapperDecelerating and Dustfree with HST: 15 SN z>1 (each SNell worth 9x SNext statistically)

Preliminary

Frieman, Jha, Kessler et al 2008

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Gravitational Weak LensingGravitational Weak Lensing

Gravitational potentials deflect light, creating convergence (magnification) and shear (shape distortion).

This depends on the focal length (geometric kernel of dldls/ds) and potential power spectrum (density growth).

Acceleration affects both distances and growth.

Convergence is very difficult to measure (no absolute size) and shear needs to be measured statistically (averaging over intrinsic ellipticities).

Need surveys with millions of well-resolved galaxies. Need good source redshift information to un-blur focal lengths.

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Weak LensingWeak Lensing

Subaru deep field 17 deg2 Miyazaki et al. 2007

CFHT Legacy Survey - Wide + Deep Semboloni et al. 2006, Hoekstra et al. 2006, Benjamin et al. 2007, Fu et al. 2008, Dore et al. 2008

For dark energy not yet precision, “pre-Boomerang”

COSMOS (HST)

2 deg2 space WL

Full tomographic analysis

Kitching, Massey, et al. 2008

Massey et al. 2007

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Baryon Acoustic OscillationsBaryon Acoustic Oscillations

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

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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Baryon Acoustic OscillationsBaryon Acoustic Oscillations

BAO need millions of galaxy positions spread over >1 Gpc3 volume, ideally spectroscopic z. Issues of nonlinearity, bias, z-space, selection effects.

Does any model agree with the data?

Galaxy selection and scale-dependent bias?

A peak? Multi-peaks?

Eisenstein et al. 2005

Sanchez & Cole 2008

Martinez et al. 0812.2154

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Precision Cosmology for Dark Energy?Precision Cosmology for Dark Energy?

Reality check - what do we really know now:

Supernovae see acceleration

Weak lensing sees dark matter

BAO sees baryons

Clusters see dark matter

Vikhlinin et al. 0812.2720

accdec

1.5 cl

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Distance ComplementarityDistance Complementarity

Distances relative to low and high redshift

have different degeneracies, hence complementarity

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Redshift RangeRedshift Range

Deep enough that is less than 10% energy density? Not next-to-dominant?

Deep enough that have accounted for >2/3 of the acceleration?

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END Lecture 1END Lecture 1

For more dark energy resources, see

http://supernova.lbl.gov/~evlinder/scires.html

Resource Letter on Dark Energy http://arxiv.org/abs/0705.4102

Mapping the Cosmological Expansion http://arxiv.org/abs/0801.2968

and the references cited therein.

Lecture 1: Dark Energy in Space

The panoply of observations

Lecture 2: Dark Energy in Theory

The garden of models

Lecture 3: Dark Energy in your Computer

The array of tools – Don’t try this at home!