1 1 Eric Linder University of California, Berkeley Lawrence Berkeley National Lab Seeing Darkness: The New Cosmology

2 2 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.

3 3 Matter Dark energy Today Size=2 Size=4 Size=1/2Size=1/4 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?

4 4 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

5 5 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!) Supernovae: direct probe of cosmic expansion Time: % of present age of universe (When you were 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.

6 6 Standard Candles Brightness tells us distance away (lookback time) Redshift measured tells us expansion factor (average distance between galaxies)

7 7 Images Spectra Redshift & SN Properties dataanalysisphysics 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

8 8 Astrophysical Uncertainties SystematicControl Host-galaxy dust extinction Wavelength-dependent absorption identified with high S/N multi-band photometry. Supernova evolutionSupernova subclassified with high S/N light curves and peak- brightness spectrum. Flux calibration errorProgram to construct a set of 1% error flux standard stars. Malmquist biasSupernova discovered early with high S/N multi-band photometry. K-correctionConstruction of a library of supernova spectra. Gravitational lensingMeasure 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.

9 9 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 Linder & Miquel 2004 No extinction (perfect) Extinction correction W With AV bias With AV+RV bias Current data quality

10 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

11 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.

12 Dark Energy – The Next Generation colorfulcolorful wide GOODS HDF 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

13 Exploring Dark Energy

14 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)

15 Equation of State Reconstruction from EOS:  (a) =    c exp{ 3  dln a [1+w(z)] }  (a) =  dln 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. . . .

16 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  + 3H  = -dV(  )/d  ¨˙

17 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/

18 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, Coupling: w eff =w-  /(3H) Turner 1985, Linder 1988, Linder 2005 Curvature:  total >1 (k>0) +   w eff < -1 Linder Climbing field (or k-essence) Csaki, Kaloper, Terning Two components, e.g. brane+  Lue & Starkman 2004, CKT 2005

19 Expansion History Suppose we admit our ignorance: H 2 = (8  /3)  m +  H 2 (a) Effective equation of state: w(a) = -1 - (1/3) dln (  H 2 ) / dln 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

20 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 ]

21 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, cf. Lue, Scoccimarro, Starkman Phys. Rev. D 69 (2004) for braneworld perturbations

22 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  = [1+w(z=1)] Works to 0.05 – 0.2%! Linder 2005 PRD; astro-ph/

23 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.

24 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/

25 Going Nonlinear Efficient generation of grid of dark energy cosmologies [w(z)] New discovery: growth  d lss So our prescription automatically “includes” CMB priors!

26 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. SNAP constraints superacceleration R = (1-q)/2

27 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?