Advances and Opportunities in Cosmology
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Advances and Opportunities in Cosmology. a t KASI. Eric Linder 23 September 2013. Berkeley Center for Cosmological Physics. Role of Observations. 빨강모자 소녀. But  , what big teeth you have! . Before we jump into bed with  , we should be sure it is not something more beastly. .

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Eric Linder 23 September 2013

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Eric linder 23 september 2013

Advances and Opportunities in Cosmology


Eric Linder

23 September 2013

Berkeley Center for Cosmological Physics

Role of observations

Role of Observations

빨강모자 소녀

But , what big teeth you have!

Before we jump into bed with , we should be sure it is not something more beastly.

Role of theory

Role of Theory

  • Cosmic acceleration and dark energy are fundamental mysteries in understanding our universe.

  • Copernican Principle / Cosmic Modesty:

  • Our galaxy is not the center of the universe.

  • Our particles are not the matter/energy of the universe.

  • Is our vacuum the vacuum of the universe?

  • Is our gravity the gravity of the universe?

Are we done

Are We Done?





There is a long way to go still to say we have measured dark energy!

Nature of dark energy

Nature of Dark Energy

Dark energy is very much notthe search for one number, “w”.

Dynamics: Theories other than  give time variation w(z). [SN+CMB/BAO]

Degrees of freedom: Quintessence has sound speed cs2=1. But generally w(z), cs2(z). Is DE cold (cs2<<1), enhance perturbations? [CMB lensing, WL]

Persistence: Is there early DE (at z>>1)? (zCMB)~10-9but observations allow 10-2. [CMB, CMB x Galaxies]

Test Gravity: Expansion vs growth [SN/BAO + CMBlens/WL/Gal]

1 dynamics

1. Dynamics

de Putter & Linder 2008

This is from physics (Linder 2003). It has nothing to do with a Taylor expansion.


Models have a diversity of behavior, within thawing and freezing.

But we can calibrate w by “stretching” it: ww(a)/ a. Calibrated parametersw0, wa.

thawing 


Caldwell & Linder 2005

The two parameters w0, wa achieve 10-3 level accuracy on observables d(z), H(z).

2 persistence

2. Persistence

We have 7 orders of magnitude of unexplored DE(zrec)=10-[2-9]Was there early acceleration (solve coincidence)? Was there early dark energy?

Effect of 0.1 e-fold of acceleration

Post-recombination, peaks left and adds ISW. Pre-recombination, peaks right and adds SW.

Current acceleration unique within last factor 100,000 of cosmic expansion!

Linder & Smith 2010

Early expansion

Early Expansion

Fit real Planck data (+WP) to any deviation from CDM in bins of log a = [-5,-4], [-4,-3.6], [-3.6,-3.2], [-3.2,-2.8], [-2.8,0].

Basically testing standard radiation/matter domination in a model independent way.

Hojjati, Linder, Samsing 2013

Slight hint of extra radiation energy, i.e. Neff=3.35.

3 perturbations microphysics

3. Perturbations / Microphysics

DE internal degrees of freedom can give rise to DE perturbations (inhomogeneity).

Only significant when 1+w is not small. Since <w(z<1)> ~ -1, this implies need early dark energy.

Perturbations only grow outside the sound horizon ~ cs/H so we need the sound speed cs<<1.

Thus persistence early dark energy.

Degrees of freedom cold early dark energy.

(These go together in many classes of DE theories, e.g. Dirac-Born-Infeld or string dilaton)

Cmb lensing

CMB Lensing

CMB as a source pattern for weak lensing. Probes z~1-5 effects, e.g. neutrino masses and early dark energy.

Planck gets ~25σfor  from CMB lensing.

Cmb lensing and cold ede

CMB Lensing and Cold EDE

DE perturbations affect matter power spectrum and so CMB lensing. cs≠1? cvis≠0? Hu 1998






Calabrese+ 1010.5612

4 test gravity

4. Test Gravity

Test gravity in model independent way.

Gravity and growth: Gravity and acceleration:

Areandthe same?(yes, in GR)

Tie to observations via modified Poisson equations:

Glight tests how light responds to gravity: central to lensing and integrated Sachs-Wolfe.

Gmatter tests how matter responds to gravity: central to growth and velocities ( is closely related).

cfBertschinger & Zukin 2008, Song+ 2011

Extending gravity

Extending Gravity

Interesting recent theories extending gravity for cosmic acceleration often have shift symmetries (ϕ ϕ+c) and higher order kinetic terms (ϕμϕμ, related to higher dimensions or massive gravity).

From Horndeski general scalar-tensor theory, Charmousis+ 2011 found “Fab 4” unique self tuning terms. Appleby, De Felice, Linder 2012 promote to nonlinear, mixed function.


Fab 5 accelerates, has tracker, dS attractor, no extra dof! – and self tuning.

It makes  invisible!


also see Padilla & Sivanesan 2013

Chasing down cosmic acceleration

Chasing Down Cosmic Acceleration

  • How can we measure dark energy in detail?

  • A strong program of techniques is in place, but new, complementary probes offer exciting prospects.

  • Measuring distance to 1%

  • with strong lensing time delays

  • Measuring growth and gravity

  • to %-level with redshift space

  • distortions

Strong lensing time delays

Strong Lensing Time Delays

Strong gravitational lensing creates multiple images (light paths) of a source.

When the source is variable (quasar / AGN), we can measure the time delays between the images. This probes the geometric path difference (cosmology) and the lensing potential (dark matter).

Key parameter is a distance ratio, the time delay distance

Time delays supernovae

Time Delays + Supernovae

Lensing time delays give superb complementarity with SN distances plus CMB.

T to 1% for zl=0.1, 0.2,… 0.6

SN to 0.02(1+z)mag for z=0.05, 0.15... 0.95


Factor 4.8 in areaΩm to 0.0044 h to 0.7% w0 to 0.077 wa to 0.26 immunizes vs curvature

Linder 2011

Strong lensing distance surveys

Strong Lensing Distance Surveys

Best current distances at 5% accuracy (16 systems known, 2-5 at 5%). 5 year aim: 25 systems, 5% accuracy = 150 orbits HST. Long term: 1% distances.

Need 1) high resolution imaging for lens mapping / modeling, 2) high cadence imaging, 3) spectroscopy for redshift, lens velocity dispersion, 4) wide field of view for survey.

Synergy: HST/GMT+ LSST/Euclid.Only low redshift z<0.6 needed for lenses.

EACOA partner ASIAA has lens modeling expertise

KASI Opportunity –

- Time domain monitoring (1-2m telescope, CosmoGrail)- AGN flux and time variation expertise -GMT (AO): highest resolution ground telescope - Cosmology expertise on joint probe analysis

Measuring time delays

Measuring Time Delays

One of the challenges is measuring time delays between images in the presence of 1) noise, 2) gaps, 3) variability, 4) microlensing.

We use Gaussian Process statistics to find a family of light curves fitting the data, with correlations. See Holsclaw+ 2010a,b,2011; Kim, Linder, Shafieloo 2012,2013 for applications to cosmology.

Lsst data challenge

LSST Data Challenge

Hojjati, Kim, Linder 2013

Blind fits:


Real data: accurate and more precise than literature.

Precision: ~2x improvement (1-2%)

Accuracy: within 0.35σ(blind challenge)

LSST Data Challenge: “Ladder of Evil” LSST will be a lens finding factory, ~8000 lensed AGN.

Strong lensing probes dark energy and dark matter.

Eric linder 23 september 2013

Higher Dimensional Data

Cosmological Revolution:

From 2D to 3D – CMB anisotropies to tomographic surveys of density/velocity field.

Data, Data, Data – CMB maps l2~10M modes; BOSS maps k3V~0.4M modes; DESI 15M modes

Redshift space distortions

Redshift Space Distortions

Redshift space distortions (RSD) map velocity field along line of sight. Gets at growth rate f, one less integral than growth factor (like H vs d).


Linder 2005

gravitational growth index 

Hume Feldman

Beyond linear

Beyond Linear

Kaiser formula inaccurate

Even monopole (average over RSD) is poor.

Anisotropic redshift distortion hopeless – without better theory.

k (h/Mpc)

Major approaches are high order perturbation theory, computational simulations – or a new combination of the two.

High order perturbation theory

High Order Perturbation Theory

Putting a rigorous formalism into place:

High order perturbation theory1

High Order Perturbation Theory

Applying perturbation theory to simulation and data:

Density growth

Velocity growth



Song, Okumura, Taruya 2013


Hubble parameter

Simulations analytics

Simulations + Analytics

Simulations allow calibration of RSD into nonlinear regime, where most of the information is.

Perturbation theory informs analytic form for linear  nonlinear transformation.

Ptrue(k,)=F(k) Plin(k,)

Kwan, Lewis, Linder 2012

Use simulations to calibrate A, B, C(k,z).


Simulations to fit rsd

Simulations to Fit RSD

First results: KLL analytic reconstruction form is accurate to 2-5% out to k=0.5 h/Mpcforz=0-2.


Vallinotto & Linder 2013

Dark energy spectroscopic instrument

Dark Energy Spectroscopic Instrument

DESI on the Mayall Telescope, Kitt Peak

3D maps of z=0-3.5 20M galaxies, quasars

KASI Opportunity –

-Spectrocopic survey in optical/NIR - Fiber optic engineering and testing - Cosmology expertise on BAO, RSD (growth/gravity) - High performance computing (KISTI partner?)

Dark energy spectroscopic instrument1

Dark Energy Spectroscopic Instrument


2.5M QSO



100% dark time

DOE granted “mission need” 2012

$2.1M Moore grant 2013

CDR milestone Jan 2014

Survey start 2018

KASI Opportunity –

-Spectrocopic survey in optical/NIR - Fiber optic engineering and testing - Cosmology expertise on BAO, RSD (growth/gravity) - High performance computing (KISTI partner?)

Testing gravity

Testing Gravity

Model independent tests of gravity: two functions, at high/low z, high/low k (8 tests). Simultaneous fit for gravity, expansion (w0, wa), galaxy bias (27 bins).


Fit all Fix to Fix to b~1/D

Daniel & Linder 2013



  • Dark energy is not the search for one number “w”. Explore dynamics, degrees of freedom, persistence. Measuring the growth history, testing growth vs expansion, probes dark energy, gravity, dark matter.

  • Strong program in place + new probes

  • Strong lensing time delays [HST/GMT; LSST]

  • Redshift space distortions [DESI]

  • Cosmology at KASI well positioned to use its existing strengths and develop new ones.

  • Science overlap with several groups: GMT, AGN, IR, spectroscopy, fibers. Partnering: ASIAA, KISTI.

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