1. * The collection of powerful ideas formerly known as String Theory Dark Energy: 2020 Vision DPF SNOWMISS SLAC Cosmic Frontier Workshop 6 to 8 March 2013 Michael S. Turner Kavli Institute for Cosmological Physics

2. Remarkable time in cosmology (Golden Age??) driven by powerful ideas and powerful instruments, revealing deep connections between quarks and the cosmos

3. Michael S Turner The pillars of cosmology are rooted in particle physics Inflation: brief period of rapid (accelerated) expansion accounts for smoothness, flatness; heat of the big bang; and seed inhomogeneities Particle dark matter: bulk of the dark matter that holds the Universe together resides in a sea of elementary particles left over from the big bang Dark energy: cause of accelerated expansion and 73% of the Universe

4. Consensus Cosmology Consensus Cosmology based upon precision measurements From quark soup to nuclei and atoms to galaxies and large-scale structure Flat, accelerating Universe Atoms, exotic dark matter & dark energy Consistent with inflation Precision cosmological parameters –Ω 0 = 1.005 ± 0.006 (uncurved) –Ω M = 0.273 ± 0.014 –Ω B = 0.046 ± 0.0016 –Ω DE = 0.73 ± 0.015 –H 0 = 70.4 ± 1.3 km/s/Mpc –t 0 = 13.75 ± 0.11 Gyr –N ν = 3.86 ± 0.42 Consistent with all data, laboratory and cosmological!

5. Michael S Turner The Universe circa 380,000 yrs WMAP ±0.001% Fluctuations

6. Michael S Turner Curve = concordance cosmology

7. Michael S Turner Consensus Cosmology DARK MATTERDARK ENERGY INFLATION Rests upon three mysterious pillars All implicate new physics!

8. Best Direct Evidence for New Physics Dark Matter Inflation Dark Energy Michael S Turner

9. The Discovery Data Perlmutter et al, 1999 Riess et al, 1998

10. … and Dr. Sandage, H 0 is now measured and q 0 is negative!

11. Carl Sagan: Extraordinary Claims Require Extraordinary Evidence

12. More SNe data, more methods (BAO, CL, ISW, growth of structure) – stronger signal

13. Michael S Turner Ω Λ = 0.727 ± 0.015 Certified by Sweden!

14. So, it’s Lambda??!## Michael S Turner Λ

15. Why isn’t lambda good enough? Short answer: no good theory for it!

16. The theory menu Vacuum energy Landscape Rolling scalar field (quintessence) Very elastic topological defects Modified gravity Dark energy/dark matter models Hole in the Universe ?? All have profound implications for both cosmology and particle physics

17. Two Big Dark Questions “break the null hypothesis: Λ + GR” Does Dark Energy change with time? (i.e., is dark energy vacuum energy) Does Cosmic Acceleration require going beyond General Relativity? No, at the 10% level Not well tested

18. Michael S Turner w = -1.07 ± 0.08 Sullivan et al 2011 Constant w dark energy

19. Michael S Turner Sullivan et al 2011 w a = -0.98 ± 1.1 w 0 = -0.91 ± 0.2 w = w 0 + w a (1 – a)

20. Strategy Circa 2006 Four methods: WL, BAO, SNe, Clusters Strategy: Narrow down to two major projects from diversity of stage I and II efforts Stage III –South Pole Telescope (CL) –Dark Energy Survey (WL, BAO, SNe, CL) –BOsS (BAO) –… Stage IV –LSST: WL, BAO, (SNe) –JDEM: WL, BAO, SNe

21. Michael S Turner Four “Stage IV” Futures

22. 1. w = -1 & theory breakthrough Percent level measurements of w and w a and LSS consistent with ΛCDM + Theoretical understanding of small vacuum energy  Problem Solved for Cosmologists and Particle Physicists

23. 2. “w = -1” & theory breakthrough Percent level measurements of w and w a and LSS consistent with ΛCDM + New compelling theoretical prediction for time variation of w and/or w a – just beyond the reach of Stage IV  Problem Solved for Cosmologists, Particle Physicists think about Stage V

24. 3. “w ≠ -1” or w a ≠ 0 Detection of signature that DE is not vacuum energy  Potential implications for both particle physics and cosmology With or without theoretical breakthrough both Cosmologists, Particle Physicists think about what to measure in Stage V

25. 4. w = -1 & no theory breakthrough Percent level measurements of w and w a and LSS consistent with ΛCDM + No theoretical understanding of small vacuum energy  Problem solved for cosmologists, but not for particle physicists “Time out”: take a break and think hard about what to do next

26. That was then, this is now

27. Now DES: WL, CL, SNe, BAO (also SPT, CL) BOsS: BAO Ahead LSST (2020?): WL, BAO, (SNe) Euclid (2020?): WL, BAO, RSD – New! MS-DESI N/S(pre-2020?): BAO, RSD e Rosita (201?): CL Also ahead (less certain, some just ideas) WFIRST (202?): SNe, WL, BAO BAO-21 cm (post 2020): BAO z = 0.5 to 1.5

28. My Observations First, recall complementarity (cosmic/practical) WL (most powerful, fewest results), RSD (very powerful, untested), BAO (powerful, results), SNe (powerful, proven), CL (don’t forget!) Underinvested (given proven value): SNe Overinvested?: WL, BAO, RSD What about new ideas? Another falsification of Λ: clustering Missing: “regular order” Strategic narrowing/staging of efforts Natural pause between Stage IV and V

29. Path Forward Make sure current projects are as successful as possible (may provide clues) Emphasize synergy/complementarity in planning Re-think high-z SNe (e.g., WFIRST) New ideas/tests welcome/needed for beyond 2020 (e.g., clustering) Decision point for diminishing returns (where/when)

31. Youbetcha Katie, I believe in Dark Energy – we can see it from Alaska!

32. Cosmic Complementarity Supernovae: simple geometric probe; fine grained BAO: geometric + simple physics; course grained WL: geometric + dynamical, most powerful Clusters: dynamical + geometric CMB: important cosmological priors (esp. for BAO, Ω M h 2 ) LSS: dynamical tests

33. “Worldly” Complementarity Supernovae –Assumption: SNeIa are standard candles –Mature: only method that has detected acceleration by itself; warts uncovered –Narrow field –z 0.8 (space) BAO –Assumption: standard ruler + simple gravitational physics –Immature: 2 detections; systematics? –Wide field –Space and ground WL –Assumption: CDM, multi-parameter PS –Immature: technical challenges, unknown systematics, σ 8 /Ω M knowledge needed –Potentially most powerful probe –Wide field –Space and ground Clusters: –Assumption: CDM + Gaussian perturbations –Immature: first results; systematics still need to be understood –Wide field –Ground and space (x-ray)