1. Particle Theory in the 21 st Century Andreas Karch

2. The ultimate quest What are the rules that govern the world at the smallest scales? Why does the universe look the way it looks like at the largest scales? Everything else is details; and its messy and complicated (like life). The Theory of Everything

3. The Theory of Everything: The standard model Lagrangian (as of July 3 rd, 2012).

4. The Theory of Everything: Prediction: Probability to interact two Ws with TeV scale energy > 1 ??????? Solution: Higgs! Is it there?

5. The Higgs! It’s real! (or at least something pretty close to it.)

6. The Theory of Everything: Problem: Hard to calculate! Solution: Lattice (no real time, no finite density). String Theory via holography

7. The Theory of Everything: Problem: That’s it? Aren’t we missing something?!?

8. Particle Physics in the 21 st century: Open Problems within the standard model: QCD difficult to calculate. Non- perturbative. Lattice works (sometimes). Sometimes perturbation theory. Problems beyond SM: We know there is BSM (beyond the standard model) physics: Neutrino masses, Dark Matter, Dark Energy, GRAVITY.

9. BSM Physics What physics could be hiding “around the corner”? What novel experimental signatures would we be looking for? Beware the nightmare scenario: “Just the Higgs” Fortunately hints of non-Higgsness. Are they real?

10. QCD Physics What happens when baryons melt? Strongly coupled soup of quarks and gluons. What are its properties? We can realize it experimentally (heavy-ion collisions). But can we cacluate? This is the stuff the early universe was made from!

11. Applied String Theory “Holography” (and a little applied field theory)

12. Holography = Solvable Toy Model Solvable models of strong coupling dynamics. Study Transport, real time Study Finite Density Explore paradigms “beyond Landau” (Challenging in real QCD, experimentally relevant) 12 (Non-Fermi Liquids? Phase Transitions? High Tc superconductors? Topological Insulators?) Gives us qualitative guidance/intuition. Not QCD! Expect errors of order 100% better than extrapolating perturbation theory to α s ~ 1

13. Challenge for Computers: 13 e.g. Lattice QCD We do have methods for strong coupling: But: typically relies on importance sampling. Monte-Carlo techniques. weighting in Euclidean path integral. FAILS FOR DYNAMIC PROCESSES OR AT FINITE DENSITY (sign problem)

14. Holographic Toy models. 14 Can we at least get a qualitative understanding of how dynamics look like at strong coupling?

15. Holographic Toy models. 15 Can we at least get a qualitative understanding of how dynamics looks like at strong coupling?

16. Holographic Theories: 16 “Large N”: Holographic toy models have two key properties: theory is essentially classical “Large λ”: large separation of scales in the spectrum m spin-2-meson m spin-1-meson ~ λ 1/4 QCD:775 MeV1275 MeV

17. Successes and recent developments Viscosity and Hydrodynamics Energy Loss Thermalization 17

18. Viscosity of Quarks and Gluons 18

19. Shear Viscosity 19 Viscosity = Diffusion constant for momentum v Viscosity = [(force/area)] per unit velocity gradient

20. Viscosity in Heavy Ions. Au How does the almond shaped fluid expand? high pressure low pressure

21. (Shear) Viscosity η 21 (1 cp = 10 −2 p = 10 −3 Pa·s) Force per unit area per velocity gradient

22. Measuring Viscosity - an example 22 (2.3 10 11 cp)

23. Measuring Viscosity - an example 23 Recall: Viscosity of pitch: ~ 2.3 10 11 cp

24. Measuring Viscosity - an example 24 Recall: Viscosity of pitch: ~ 2.3 10 11 cp RHIC’s measurement of hot QCD (= quark gluon plasma) (from colliding high energy gold nuclei)

25. Measuring Viscosity - an example 25 Recall: Viscosity of pitch: ~ 2.3 10 11 cp RHIC’s measurement of hot QCD (= quark gluon plasma) (from colliding high energy gold nuclei)

26. Viscosity in Holography: 26 (KSS; Kovtun - UW grad student; Son – UW faculty, Starinets – UW postdoc) pinpoints correct observable gives ball-park figure large at weak coupling – extrapolation from weak coupling is order of magnitude off!

27. η/s Viscosity to entropy ratio: close to 1/(4 π) in quark gluon plasma produced at RHIC --- strongly coupled! fluid, not plasma! 2-3 times that in cold atomic gases at least factor of 10 times 1/(4 π) in all other substances known to mankind (including superfluid helium, water, …) 11 orders of magnitude larger that 1/(4 π) in pitch.

28. Energy Loss 28

29. Jet quenching. See one of two back-to- back created particles. The other one got “stuck” in the fireball Jet quenching is a direct indication of large drag forces on quarks.. Sometimes HARD COLLISIONS produce non-thermal particles inside the fire ball = probe of the plasma.

30. Jet Quenching at the LHC (Atlas)

31. Stopping Distance: Quantify Energy loss in terms of Stopping Distance: How far does quark of energy E travel before it gets thermalized into the plasma? Perturbative QCD or QED: L ~ E 1/2

32. Energy Loss: Heavy quarks v Constant E - field (Herzog, Karch, Kozcaz, Kovtun, Yaffe) (all UW: postdoc, faculty, student 2,faculty)

33. Energy Loss: Heavy quarks v Constant E - field (Herzog, Karch, Kozcaz, Kovtun, Yaffe) (all UW: postdoc, faculty, student 2,faculty) SOLVE CLASSICAL EQUATIONS OF MOTION!

34. Energy Loss, Light Quarks (Chesler, Jensen, Karch, Yaffe – again all UW)

35. Stopping Distance: Perturbative QCD: L ~ E 1/2 Holography: Maximal Stopping Distance: L ~ E 1/3 others found: Typical Stopping Distance: L ~ E 1/4 Experiment: 1/3 preferred over 1/2 ???

36. ThermalizationThermalization Why does the QCD fireball thermalize so rapidly? 36

37. ThermalizationThermalization Why does the QCD fireball thermalize so rapidly? too hard! 37

38. ThermalizationThermalization How quickly does the holographic fireball thermalize? 38

39. Shockwave-collision to black hole 39 (Chesler, Yaffe) Energy/area in shock ~ μ 3

40. Shockwave-collision to black hole 40 (Chesler, Yaffe)

41. Shockwave-collision to black hole 41 (Chesler, Yaffe) μ ~ 2.3 GeV “RHIC”: Hydro valid ~ 0.35 fm/c << 1 fm/c But: there is so much more info in this plot! Lots to explore! Strong coupling, non-equilibrium.

42. Hydrolization vs Thermalization 42 (Chesler, Teaney) Note: Hydro works when transverse and longitudinal pressure differ by a factor of 2. Hydrolization before Thermalization! Hydro works. No well defined temperature.

43. Hydrolization vs Thermalization (Chesler, Teaney) t=0 initial perturbation UV IR

44. Hydrolization vs Thermalization (Chesler, Teaney) shock follows lightlike geodesic UV IR Asymptotic metric settles to final state plus small peturbations. Hydrolization

45. Hydrolization vs Thermalization (Chesler, Teaney) shock reaches near horizon region UV IR Fluctuation Spectrum thermal.. Thermalization

46. Applications to Condensed Matter Physics. 46

47. Strong Coupling in CM. 47 The theory of everything: How hard can it be?

48. Strong Coupling in CM 48 Already Helium too difficult to solve analytically. electron/electron Coulomb repulsion not weak! if it is negligible, we have good theory control: Band structure! Insulators and conductors. but what to do when it is not?

49. Landau’s paradigms: 49 Identify physical candidates for low energy degrees of freedom. Write down most general allowed interactions See how interactions scale in low energy limit dominate transport many interactions “irrelevant” = scale to zero

50. What could they be? 50 1) weakly coupled fermions. Landau Fermi Liquid Fermi Surface Low energy excitations near Fermi Surface Only Cooper Pair Instability survives at low energies, all other interactions scale to zero universal! at low temperatures resistivity grows as T 2

51. What could they be? 51 1) weakly coupled bosons. Landau’s Theory of Phase Transitions free energy order parameter = scalar field. Scalar mass relevant; dominates at low energies. Can be tuned to zero close to a phase transition.

52. Is this all? 52 Degrees of freedom in high Tc superconductors are neither! Non-Fermi Liquid at low temperatures resistivity grows as T Strange Metal

53. What else could it be? 53 This is the perfect question to ask a solvable toy model: Studying matter in holographic toy models, what are the possible low energy behaviors? Matter=finite density of some conserved charge.

54. MIT/Leiden Fermions. 54 Holographic Realization of a large class of non-Fermi Liquids. Fermions in a charged black hole background. (Lee) (Liu, McGreevy, Vegh) (Cubrovic, Zaanen, Schalm)

55. MIT/Leiden Fermions. 55 Characteristic Features: Fermi surface (singularity in wavevector dependence of correlation functions). No well defined particle excitation. (not a Fermi-liquid). Low temperature resistivity grows as T 2Δ-1 (Δ free parameter in model).

56. Interactions don’t scale away? 56 Fermi-surface, but interactions not irrelevant? Low energy physics = fermions coupled to other light degrees of freedom! Local Quantum Criticality. 0+1 dimensional theories close to a Landau-like phase transition. = AdS 2

57. The big question: 57 Is any of this realized (to some approximation) in real systems? Holography provides controlled examples of novel quantum matter.

58. Summary. 58 Solvable models of strong coupling dynamics. Holography =

59. A graduate career in theoretical physics?

60. Particle Theory Number of students >> Number of jobs Think twice! Do you like theory so much that it is worth while job insecurity for the next 10 years, taking postdocs at random, far away places?

61. Particle Theory about 5 students for 5 faculty historically paid our students 10 hour RA for 3 years; students TA at least 10 hours throughout year 1: take the graduate classes, do reading, attend particle theory journal club on Fridays to get to know us. Maybe research in the summer year 2: take QFT, advanced SM, nuclear physics, particle physics. Do trial research with one of us. year 3: we typically start supporting students we decide to take on by the beginning of their 3 rd year.