1. Accelerators in the Universe March 2008 Rocky Kolb University of Chicago Accelerators in the Universe March 2008 Rocky Kolb University of Chicago

2. Cold Dark Matter: (CDM) 25% Dark Energy (  ): 70% Stars: 0.8% H & He: gas 4% Chemical Elements: (other than H & He)  0.025% Neutrinos: 0.17% Radiation: 0.005%  CDM  inflationary perturbations  baryo/lepto genesis

3. Evidence for Dark Energy Measuring the expansion history of the Universe

4. Friedmann equation ( G   GT  ) : Expansion rate H ( z ) Equation of state parameter: w  p   w  for  if w  w ( a ): Hubble constant curvature matter radiation dark energy CMB LSS CMB H ( z ) Evolution of H(z) Is a Key Quantity

5. Age of the universe Evolution of H(z) Is a Key Quantity Many observables based on H ( z ) through coordinate distance r(z) Luminosity distance Flux = (Luminosity /  d L  ) Angular diameter distance   Physical size / d A Volume (number counts) N / V  ( z ) Robertson–Walker metric

6. Astier et al. (2006)* SNLS Einstein-de Sitter: spatially flat matter-dominated model (maximum theoretical bliss)  CDM confusing astronomical notation related to supernova brightness  brighter fainter  supernova redshift z Evidence for Dark Energy High-redshift supernova are about a half-magnitude fainter than expected in the Einstein-de Sitter model. Statements such as there is dark energy, or that the Universe is accelerating are interpretations of the observations. * Similar data from Essence collaboration.

7. MM 1. Find standard candle (SNe Ia) 2. Observe magnitude & redshift 3. Assume a cosmological model 4. Compare observations & model 5. Fit needs cosmoillogical constant or vacuum energy density Astier et al. (2006) SNLS Einstein–de Sitter model Evidence For Dark Energy Evidence For Dark Energy Assumes w  (i.e.,  ) Assumes priors on H , spatial flatness, etc. 2.0 1.5 1.0 0.5 0 0 0.5 1.0 

8. (The Unbearable Lightness of Nothing)  V  10 –30 g cm  !!!!!  V   G  V length scale   cm   cm mass scale   eV   eV Cosmoillogical Constant

9. All fields: harmonic oscillators with zero-point energy Cosmoillogical Constant

10.  The quantum vacuum has a Higgs potential  Higgs potential gives mass to quanta like quarks and electrons e,W, Z, quarks … photon Higgs potential:     eV Cosmoillogical Constant   

11. The Higgs Bison at Fermilab

12.  high- temperature low- temperature VV Cosmoillogical Constant  V 

13. Cosmoillogical Constant Extra Dimensions

14. Illogical timing (cosmic coincidence): Cosmoillogical Constant We are here

15. Astier et al. (2006)* SNLS Einstein-de Sitter: spatially flat matter-dominated model (maximum theoretical bliss)  CDM confusing astronomical notation related to supernova brightness supernova redshift z Evidence for Dark Energy 3) Baryon acoustic oscillations 4) Weak lensing 1) Hubble diagram (SNe) 2) Cosmic Subtraction The case for  : 5) Galaxy clusters 6) Age of the universe 7) Structure formation * Similar data from Essence collaboration.

16. cmb dynamicsx-ray gaslensing simulations power spectrum  TOTAL    M    B  CMB many methods CMB/BBN    Evidence for Dark Energy

17. How We “Know” There’s Dark Energy Assume model cosmology: – General relativity – Homogeneity & isotropy (FLRW) – Energy (and pressure) content:    M   R    +  – Input or integrate over cosmological parameters: H ,  , etc. Calculate observables d L (z), d A (z), H(z),  Compare to observations Model cosmology fits with  , but not without   All evidence for dark energy is indirect : observed H(z) is not described by H ( z ) calculated from the Einstein-de Sitter model [spatially flat (from CMB) ; matter dominated (  M )] G  = 8  G T 00 H 2   G  /  k/a 2

18. Taking Sides! Can’t hide from the data –  CDM too good to ignore – SNe – Subtraction:  – Baryon acoustic oscillations – Galaxy clusters – Weak lensing – … H(z) not given by Einstein–de Sitter G  (FLRW)    G T  (matter) Modify left-hand side of Einstein equations (  G  ) 1. Beyond Einstein (non - GR: f (R), branes, etc.) 2. (Just) Einstein (back reaction of inhomogeneities) Modify right-hand side of Einstein equations (  T  ) 1. Constant (“just” a cosmoillogical constant  ) 2. Not constant (dynamics driven by scalar field: M   eV )

19. Anthropic/LandscapeAnthropic/Landscape Many sources of vacuum energy String theory has many (    ?) vacua Some of them correspond to cancellations that yield a small  Although exponentially uncommon, they are preferred because … More common values of  results in an inhospitable universe The Cosmological Constant and String Theory are made for each other… Cosmological constant (  ): A result in search of a theory String theory (or M -theory): A theory in search of a result

20. QuintessenceQuintessence Many possible contributions. Why then is total so small? Perhaps unknown dynamics sets global vacuum energy equal to zero……but we’re not there yet! V()V()  0  Requires m      eV

21. QuintessenceQuintessence Not every scalar potential works – scaling, tracking, stalking potentials Couplings to matter (dark or otherwise) – mavens (mass varying neutrinos) – chameleon (dark energy is sensitive to environment) – changing fundamental constants ( , etc.) k -essence – phantom, ghost condensate, Born-Infeld, …, Chaplygin gas Episodic dark energy (acceleration happens)

22. Punctuated Vacuum Domination Dodelson, Kaplinghat, Stewart dark energy  cosmic destiny

23. Modifying the Left-Hand Side Braneworld modifies Friedmann equation Gravitational force law modified at large distance Tired gravitons Gravity repulsive at distance R  Gpc n = 1 KK graviton mode very light, m  ( Gpc )  Einstein & Hilbert got it wrong f ( R ) Backreaction of inhomogeneities Five-dimensional at cosmic distances Deffayet, Dvali & Gabadadze Gravitons metastable - leak into bulk Gregory, Rubakov & Sibiryakov; Dvali, Gabadadze & Porrati Kogan, Mouslopoulos, Papazoglou, Ross & Santiago Csaki, Erlich, Hollowood & Terning Räsänen; Kolb, Matarrese, Notari & Riotto; Notari; Kolb, Matarrese & Riotto Binetruy, Deffayet, Langlois Carroll, Duvvuri, Turner, Trodden

24. Acceleration from Inhomogeneities Homogeneous modelInhomogeneous model We think not! (Buchert & Ellis)

25. Acceleration from Inhomogeneities No dark energy No acceleration in the normal sense (no individual fluid element accelerates)

26. Dark Energy Many theoretical approaches (none compelling i.m.o.!) Perhaps nothing more can be done by theorists …

27. "Nothing more can be done by the theorists. In this matter it is only you, the astronomers, who can perform a simply invaluable service to theoretical physics." Einstein in August 1913 to Berlin astronomer Erwin Freundlich encouraging him to mount an expedition to measure the deflection of light by the sun. Dark Energy

28. Many theoretical approaches (none compelling i.m.o.!) Perhaps nothing more can be done by theorists … Observables: d L ( z ), d A ( z ), distances, … … which (in FRW at least) all depend on H ( z ) Might as well assume FRW and measure(?) H ( z ) (Measure what you can as well as you can) Dark energy enters through   ( z ), parameterized by w ( z ) Can’t measure a function; parameterize w ( z )

29. Dark Energy  : w   ; w a  Quintessence:   w    /  ; w a  model dependent Modified gravity: w  can be less than  ; w a unconstrained Back reactions:?????

30. DETF* Experimental Strategy: Determine as well as possible whether the accelerating expansion is consistent with being due to a cosmological constant. (Is w  ?) If the acceleration is not due to a cosmological constant, probe the underlying dynamics by measuring as well as possible the time evolution of the dark energy. (Determine w ( a ).) Search for a possible failure of general relativity through comparison of the effect of dark energy on cosmic expansion with the effect of dark energy on the growth of cosmological structures like galaxies or galaxy clusters. (Hard to quantify.) * Dark Energy Task Force

31. Observational Program source? strong lensing

32. Astier et al. (2006) SNLS Einstein-de Sitter: spatially flat matter-dominated model (maximum theoretical bliss)  CDM confusing astronomical notation related to supernova brightness supernova redshift z Evidence for Dark Energy 3) Baryon acoustic oscillations 4) Weak lensing 1) Hubble diagram (SNe) 2) Cosmic Subtraction The case for  : 5) Galaxy clusters 6) Age of the universe 7) Structure formation

33. Supernova Type Ia Measure redshift and intensity as function of time (light curve) Systematics (dust, evolution, intrinsic luminosity dispersion, etc.) A lot of information per supernova Well developed and practiced Present procedure: – Discover SNe by wide-area survey on 4m-class telescopes – Follow up spectroscopy (lots of time on 8m-class telescopes) The future: – Better systematics (space-based?) – Huge statistics (say with LSST) with photometric redshifts

34. Each overdense region is an overpressure that launches a spherical sound wave Wave travels outward at c /  3 Photons decouple, travel to us and observable as CMB acoustic peaks Sound speed plummets, wave stalls Total distance traveled 150 Mpc imprinted on power spectrum WMAP SDSS Baryon Acoustic Oscillations

35.  Mpc  d A   Mpc  H   z Baryon Acoustic Oscillations Acoustic oscillation scale depends on  M h  and  B h   (set by CMB acoustic oscillations) It is a small effect (  B h  ¿  M h  ) Dark energy enters through d A and H

36. Virtues – Pure geometry. – Systematic effects should be small. Problems: – Amplitude small, require large scales, huge volumes – Photometric redshifts? – Nonlinear effects at small z, cleaner at large z  Dark energy not expected to be important at large z Baryon Acoustic Oscillations

37. Weak Lensing dark energy affects growth rate of M dark energy affects geometric distance factors observe deflection angle D OS D LS  b

38. Weak Lensing Dominant source is PSF of atmosphere and telescope Errors in photometric redshifts Space vs. Ground: Space: no atmosphere PSF Space: Near IR for photo- z ’s Ground: larger aperture Ground: less expensive The signal from any single galaxy is very small, but there are a lot of galaxies! Require photo- z ’s? Current projects – 100’s of sq. degs. deep multicolor data – 1000’s of sq. degs. shallow 2-color data DES (2010) – 1000’s of sq. degs. deep multicolor data LSST (2013) – full hemisphere, very deep 6 colors Systematic errors:The Landscape:

39. Galaxy Clusters Cluster redshift surveys measure cluster mass, redshift, and spatial clustering Sensitivity to dark energy volume-redshift relation angular-diameter distance–redshift relation growth rate of structure amplitude of clustering Problems: cluster selection must be well understood proxy for mass? need photo- z ’s

40. CMBWMAP 2/3WMAP 5 yr PlanckPlanck 4yr ClustersAMI SZA APEX AMIBA SPT ACT DES SNe Pan-STARRS DESLSST JDEMSDSS CFHTLS CSP ATLAS SKAFMOSWFMOS SDSS LensingCFHTLS ATLASKIDS DES, VISTA JDEM LSSTSKA Pan-STARRS SUBARU 2020 2008 ESSENCE XCS DUNE 2010 BAOLSST SDSSDLS LAMOST Hyper suprime DES, VISTA,VIRUS Pan-STARRS Hyper suprime JDEM What’s Ahead 2015 Roger Davies

41. Conclusions: Two Sides to the Story 1.Right-Hand Side: Dark energy “constant” vacuum energy, i.e.,  time varying vacuum energy, i.e., quintessence 2.Left-Hand Side Modification of GR Standard cosmological model (FLRW) not applicable The expansion history of the universe is not described by the Einstein-de Sitter model. Explanations: 1.Well established: Supernova Ia 2.Circumstantial: subtraction, age, structure formation, … 3.Emergent techniques: baryon acoustic oscillations, clusters, weak lensing Phenomenology: 1.Measure evolution of expansion rate: is w  ? 2.Order of magnitude improvement feasible

42. Accelerators in the Universe March 2008 Rocky Kolb University of Chicago Accelerators in the Universe March 2008 Rocky Kolb University of Chicago