# Presentation: 470560

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

**Seeing Darkness:**    **The New Cosmology**

## New Frontiers

**Beyond Einstein:**** What happens when gravity is no longer an attractive force?**

- Scientific American

**Discovery**** ****(****SCP,HiZ 1998****)****:**** ****70% of the universe acts this way! **
***Fundamentally new physics.****** Cosmology is the key.****** ***

## Cosmic Coincidence

**Matter**

**Dark energy**

**Today**

**Think of the energy in ******** as the level of the quantum “sea”.  At most times in history, matter is either drowned or dry.**** **

**Cosmic Coincidence**

**Is this mysterious dark energy the original ****cosmological constant ********, a quantum zeropoint sea?**** **

## On Beyond !

***We need to explore further frontiers***** in high energy physics, gravitation, and cosmology.**
** **
**New quantum physics?**** ****Does nothing weigh something?**** ****Einstein’s cosmological constant****,**** Quintessence****, ****M/String theory**** **
**New gravitational physics? ****Is nowhere somewhere?**** ****Quantum gravity, supergravity, extra dimensions?**** **
**We need new, highly precise data**

## Cosmic 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*****!)**

## Standard Candles

**Brightness tells us distance away (lookback time)**
**Redshift measured tells us expansion factor (average distance between galaxies)**

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

*Images*

*Spectra*

*Redshift & SN Properties*

**data**

**analysis**

**physics**

**Nature of**
**Dark Energy**

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

- What makes SN measurement special?** ****Control of systematic uncertainties**

## Astrophysical 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.**

## Beyond 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**

## Gravitational 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**** **

## Gravitational 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****.**

## Dark Energy – The Next Generation

**c****o****l****o****r****f****u****l**

- wide

**9000******** the Hubble Deep Field**
***plus***** 1/2 Million ******** HDF**

**deep**

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

**Both optical and infrared wavelengths to see thru dust.**

**SNAP: Supernova/Acceleration Probe**

## Exploring Dark Energy

**Exploring Dark Energy**

## Quintessence

**Scalar field ***********  *****with Lagrangian***** *****L*********** *****= (1/2)(******************)****2 ****- V(**********)**** **

**Energy density****  ****	************** = (1/2) *********** *****2**** + V(**********)**
**Pressure**** ****	****	****p********** = (1/2) *********** *****2**** - V(**********)**

**.**

**.**

**Einstein gravity says gravitating mass ********+3p****, so  acceleration if ****equation of state ratio****  w = p/******** < -1/3**
**w = (K-V) / (K+V)**
**Potential energy dominates (slow roll): ****V >> K ******** w = -1**
**Kinetic energy dominates (fast roll): ****K >> V ******** w = +1**
******(a) ~ e****3********dln a [1+w(a)] ****~ a****-3(1+w)**
**Dynamics important! Value and running: *****w*****, *****w************=w******a ******/2***** ****Equation of state model *****w(a) = w******0******+w******a******(1-a)***

## Equation of State

**Reconstruction from EOS:**** **
**	********(a) = *************** *********c**** exp{ 3 ********d*****ln***** a [1+****w(z)****] }**
***	***********(a) = ********d*****ln***** a H****-1**** sqrt{ ********(a) [1+****w(z)****] }**
**	****V(a) = (1/2) ********(a) [1-****w(z)****] **
**	****K(a) = (1/2)*****   *****2**** = (1/2) ********(a) [1+****w(z)****] **

**But,****    ~ ********[(1+w)********] ~ ********(1+w) HM****p**
**So if ****1+w << 1****,**** ****then ************** ~    /H << M****p****.  **
**It is very hard to directly reconstruct the potential. **

## Dynamics of Quintessence

**Equation of motion of scalar field**
** ****driven by steepness of potential**
** ****slowed by Hubble friction**
**Broad categorization -- which term dominates: **
** ****field rolls but decelerates as dominates energy **
** ****field starts frozen by Hubble drag and then rolls **
**	****	****Freezers vs. Thawers**

## Limits of Quintessence

**Distinct, narrow regions of ****w-w******
**Works for: ****linear, quadratic, quartic, PNGB,****	********-n****,**** ****SUGRA, exponential**

**Entire “thawing” region looks like ****w****constant****= -1±0.05****.  ****Need w******** experiments with ******** (w********) ≈ 2(1+w)****.**

**Caldwell & Linder 2005 PRL; astro-ph/0505494**

## Phantoms without Ghosts

**5 Ways to have w < -1 without “bad” physics:**

***What do you mean bad?******	******	******	******	******	******	****** Imagine all life as you know it stopping instantaneously and every molecule in your  body exploding at the speed of light.***** ****-- Ghostbusters**

** ****Vacuum metamorphosis ****Parker & Raval 1999: PRD 60, 063512**
** ****Coupling: w****eff****=w-********/(3H) ****Turner 1985, Linder 1988, Linder 2005**
** ****Curvature: ********total****>1 (k>0) + ******** ******** ****w****eff**** < -1 ****Linder 0508333**
** ****Climbing field (or k-essence) ****Csaki, Kaloper, Terning 0507148**
** ****Two components, e.g. brane+******** ****Lue & Starkman 2004, CKT 2005**

## Expansion History

**Suppose we admit our ignorance:**
**	****H****2**** = (8********/3) ********m**** + ********H****2****(a)**
**Effective equation of state:**
**w(a) = -1 - (1/3) d*****ln *****(********H****2****) / d*****ln***** a**
**Modifications of the expansion history are equivalent to time variation w(a).****  ****Period.**** **

**Observations that map out expansion history a(t), or w(a), tell us about the ****fundamental physics of dark energy.**
**Alterations to Friedmann framework ******** *****w(a)***

- gravitational extensions or high energy physics

## Expansion History

**For modifications ********H****2****, define an effective scalar field with**
**  ****V = (3M****P****2****/8********) ********H****2**** + (M****P****2****H****0****2****/16********) [ d ********H****2****/d *****ln *****a] **
**  ****K = - (M****P****2****H****0****2****/16********) [ d ********H****2****/d *****ln *****a] **
**Example:**** ********H****2**** = A(********m****)****n**** **
**	****w = -1+n**
**Example:**** ********H****2**** = (8********/3) [f(********m****) - ********m****]**
**	****w= -1 + (f********-1)/[ f/********m**** - 1 ]**

## Revealing Physics

** ****Time variation w****(z) is a critical clue to fundamental physics. **
** ****Modifications of the expansion history = w(z).**
** ****But need an underlying theory - ********? beyond Einstein gravity?**
**	****Growth history and expansion history work together. **

- Linder 2004, Phys. Rev. D 70, 023511* cf.* Lue, Scoccimarro, Starkman      Phys. Rev. D 69 (2004) 124015           for braneworld perturbations

## Physics of Growth

**Growth**** ****g(a)=(********/********)/a**** depends purely on the expansion history ****H(z)**** -- *****and***** ****gravity theory****.  **

**Expansion effects via w(z), but *****separate***** effects of gravity on growth. **

**g(a)**** = exp { ********0****a****d ln a [********m****(a)******** ****-1] }**

**Growth index**** ******** ****= 0.55+0.05[1+w(z=1)]**** ****	****Works to 0.05 – 0.2%!**

**Linder 2005 PRD; astro-ph/0507263**

## Growth and Expansion

**Keep expansion history as w(z), growth deviation from expansion by ********. **

**With ******** as free fit parameter, we can test framework, and the origin of dark energy. **

**New paradigm: ****	****	****To reveal the origin of dark energy, measure ****w****, ****w********, and ********.****  ****	****	****e.g. use SN+WL.**

## Going Nonlinear

**This gives a high accuracy approach to growth factor, i.e. ****linear**** mass power spectrum.  Can we get high accuracy for the ****nonlinear**** power spectrum?**

**New prescription: **
** ****Normalize ****g****today****, i.e. scale by ********8****. **
** ****Match different cosmologies’ (i.e. ****w****’s) growth at z=1.8; this determines ********M****. **
** ****Fix ****h**** by using invariant ********M****h****2****.**

**It works!**** ****Relative precision on**** ****P****k****full**** to <1.5%**** ****over z=0-3. **
**NB: ****fit functions were only good to ~10% -- for ********.**** **

**Linder & White, Phys. Rev. D Rapid; astro-ph/0508401**

## Going Nonlinear

**Efficient generation of grid of dark energy cosmologies [****w(z)****] **

**New discovery:****   ****growth ******** d****lss ****	****	****	****	****	****So our prescription automatically “includes” CMB priors!**** **

## Today’s Inflation

**Map the expansion history precisely and see the transition from acceleration to**** ****deceleration.**** **
**Test the ****cosmology framework**** – alternative gravitation, higher dimensions, etc.**

## The Next Physics

**The ****Standard Model gives us commanding knowledge about physics ****	****	****	****	****	**** -- 5% of the universe (or 50% of its age).**
**What is dark energy?**
**	****Will the universe expansion accelerate forever?**
**	****	****Does the vacuum decay? Phase transitions?**
**How many dimensions are there? **
**	****How are quantum physics and gravity unified? **
**	****	****What is the fate of the universe? **
**That 5% contains two fundamental forces and a zoo of elementary particles.**
**What will we learn from the dark sector?!**

**How can we *****not***** seek to find out?**