# Presentation: 682343

**Eric Linder **
**University of California, Berkeley**
**Lawrence Berkeley National Lab**

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

**JDEM constraints**

## Outline

**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!**

## Describing Our Universe

- STScI

**95% of the universe is unknown!**

***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**

## Mapping History

**Mapping History**

## Acceleration

**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**

## Windows 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)****. **

## 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 years**

## Cosmic Archaeology

**CMB: direct probe of quantum fluctuations**
**Time: 0.003% of the present age of the universe. **

## BREAK

**CMB**

## 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. **

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

## CMB 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 *****c******s******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**

## Mapping 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

## Type 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”

## Type Ia Supernovae

**Redshift tells us the expansion factor *****a***

- Time after explosion

- Brightness

**Brightness tells us distance away (lookback time *****t*****)**

## Standardized Candles

**Supernova Legacy Survey (SNLS)**

**Conley et al 2006**

## Understanding Supernovae

**Understanding Supernovae**

- 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**

## Current Data: World

**Union SN Set**
** ****Complete reanalysis, refitting of 13 SN data sets**
** ****396 SNe Ia (58+249) - new low z SN**
** ****Fit ********M****i**** 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]**

## 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]**

## Current Data: SNLS

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

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

## Imminent 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, SkyMapper**
**Decelerating and Dustfree with HST: 15 SN z>1 ****	****	****(each SN****ell**** worth 9x SN****ext**** statistically)**

***Preliminary***

**Frieman, Jha, Kessler et al 2008**

## Gravitational Weak Lensing

**Gravitational potentials deflect light, creating convergence (*****magnification*****) and shear (*****shape distortion*****).**
**This depends on the focal length (*****geometric kernel***** of ****d****l****d****ls****/d****s****) 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. **

## Weak Lensing

**Subaru deep field 17 deg****2**** ****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 deg****2 ****space WL**
**Full tomographic analysis**

**Kitching, Massey, et al. 2008**
**Massey et al. 2007**

## Baryon 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. **

**Galaxy cluster size**

**M. White**

## Baryon Acoustic Oscillations

**BAO need millions of galaxy positions spread over >1 Gpc****3**** 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**

## 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**

## Distance Complementarity

**Distances relative to ****low****	****	****and ****high**** redshift**

**have different degeneracies, hence complementarity**

## Redshift 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? **

## END  Lecture 1

**For more dark energy resources, see**** **
- _[http://supernova.lbl.gov/~evlinder/scires.html](http://supernova.lbl.gov/~evlinder/scires.html)_** ****	**
***Resource Letter on Dark Energy***** **_[http:](http://arxiv.org/abs/0705.4102)__[//arxiv](http://arxiv.org/abs/0705.4102)__[.org/abs/0705.4102](http://arxiv.org/abs/0705.4102)_** **
***Mapping the Cosmological Expansion***** **_[http://arxiv.org/abs/0801.2968](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!**