CGC

1. Theory Summary* QM 2006 Shanghai, China * Not comprehensive Art due to Tetsuo Hatsuda and Steffen Bass (with some artistic interpretation) CGC Initial Singularity Glasma sQGP Hadron Gas

2. Strong correspondence with cosmology. How can ideas be tested? What are the new physics opportunities?

3. The Initial Wavefunction for High Energy Baryon: 3 quarks 3 quarks 1 gluon ….. 3 quarks and lots of gluons

4. Density of Gluons Grows becomes weak Color Glass Condensate Successes: Geometric scaling in DIS Diffractive DIS Shadowing in dA Multiplicity in AA Limiting fragmentation Long range correlations Total cross section Pomeron, reggeon, odderon Break down of factorization of pp to ep? Saturated hot spots?

5. The Initial Singularity and the Glasma The hadrons pass through one another: Topological charge density is maximal: Anomalous mass generation In cosmology: Anomalous Baryogenesis Before the collision only transverse E and B CGC fields Color electric and magnetic monopoles Almost instantaneous phase change to longitudinal E and B Production of gluons and quarks from melting colored glass

6. The Initial Singularity and the Glasma Before collision, stability After collisions, unstable Quantum fluctuations can become as big as the classical field Quantum fluctuations analogous to Hawking Radiation Growth of instability generates turbulence => Kolmogorov spectrum Analogous to Zeldovich spectrum of density fluctuations in cosmology Topological mass generation Interactions of evaporated gluons with classical field is g x 1/g ~ 1 is strong Thermalization?

7. Fluctuations in The Initial Singularity During inflation: Fluctuations on scale larger than even horizon are made Late times: Become smaller than even horizon => Seeds for galaxy formation Fluctuations over many units in rapidity in initial wavefunction

8. Instabilities driven by momentum anisotropy

9. The sQGP Good agreement of “well thought out” hydro computations with radial and elliptic flow data Energy density is high enough: Very large energy loss of jets The evidence is strong that one has made a system of quarks and gluons which is to a good to fair approximation explained by a Quark Gluon Plasma

10. More evidence: Is its lower bound ? Conclusion depends on initial conditions? Coalesence models reproduce v2 at intermediate pt. Do they work too well? Energy conservation? Water Do we really need huge cross sections in transport to reproduce flow data? Has led some to suggest that we live in the best of all possible worlds!

11. Hydro plus CGC Initial Conditions Good description of multiplicity and pT distributions

12. Hydro +CGC + Jet quenching: good description of jets (except for heavy quarks!)

13. Good description of v_2 when dissipative effects in hadronic matter are included CGC Initial conditions without viscosity in QGP do less well Can and will do better: Next generation of hydro, e. g. Spherio: Fully 3-d with viscosity Need more than just running codes and fitting data! We do not yet properly treat: Thermalization. Initial conditions. Viscosity in QGP not yet treated in fully consistent way Hadronization and coalesence not fully self consistent

14. How Perfect is the sQGP? CGC Initial Conditions allow for higher hydro limit. LHC?

15. CGC Initial Conditions? Large parton cross sections not required for flow. Thermalization through mutligluon interactions? Plasma Instabilities? Viscosity effects are unknown, computation is theoretical challenge. Viscous Hydrodynamics: Becoming practical

16. Jet Correlations: Mach cones one of earliest proposals for heavy ion collisions: Greiner, Stocker and Frankfurt group Cherenkov radiation and Mach cones possible, but devil in the details Possible explanation as Sudakov form factor for jet emission by Salgado et. al? Deflected jets al a Vitev?

17. Au+Au central 0-12% ZDC Δ2 Δ1 Mach Cone: Radiation and scattering: No cone Cerenkov: Wide angles

18. Heavy Quark Energy Loss: Charm to bottom ratio consistent with expectation. QCD total cross sections off from data by factor of 2-5 What is the basic energy loss mechanism: Radiation? Elastic scattering? First principles computations are hard: Results depend on low density region Jet quenching computations not strictly perturbative.

19. String Theory and the sQGP. Bad Side: Results are for N=4 SUSY Yang Mills No running coupling constant No particle masses Strict infinite coupling limit May or may not have any qualitative relationship to QCD No limit where theory is QCD Good Side: Many proponents are shamelessly enthusiastic Can generate new ways of thinking about old problems Was derived from string but has simple interpretation: Mean free path must be bigger than De Broglie wavelength Brian Greene: “data now emerging from the Relativistic Heavy Ion Collider at BNL appear to be more accurately described using string theory methods than with more traditional approaches” <<< Is it true?

20. String vs Conventional Computation of Energy Density and Pressure Perturbation Theory: 25% off from ideal gas value Naïve perturbation theory not good Conventional method is Lattice Gauge Theory: Errors of order several % String Theory: About 10% off for energy density (scaled by number of degrees of freedom) But………

21. AdSCFT Result > Perturbative computations can be fixed. Good agreement for relatively weak coupling above Tc Difference between strongly interacting and strong coupling. String computations require coupling limit.

22. Is the coupling large? .81 2.3 .90 1.8 1.02 .7 1.5 .4 2.0 .3 Lattice Monte Carlo Intermediate to weakly coupled, but strongly interacting. AdsCFT MUST be accountable to the same scientific standards as are other computations, or else it is not science.

23. Theoretical Issues: Many problems of deep significance. Conceptual and computational. Issues must be scientific: Controlled approximation A result must be falsifiable. “Theoretical physics must be done with passion and enthusiasm”