1. Phenomenology from AdS/CFT pre-equilibrium flow in pA and AA
Paul Romatschke, CU Boulder & CTQM & JET Collaboration

2. This makes HIC phenomenology more predictive and more realistic
Motivation
I argue that we want hydro initial conditions from a dynamic model that incorporates equilibration because
Reduces the number of parameters (e.g. τhydro) w.r.t non-thermalizing models
Naturally includes pre-equilibrium flow
This makes HIC phenomenology more predictive and more realistic

3. Motivation
In principle, any model describing dynamic equilibration in HIC will do
In practice, the choices we have are:
N=4 SYM at strong coupling via AdS/CFT; Problems: not QCD; validity at g~1?
PQCD (e.g. parton cascade); Problem: validity at g~1?
CGC/Plasma Inst.: via CYM/Boltzmann simulations; Problems: groups disagree on equilibration/validity at g~1?

4. Motivation
In principle, any model describing dynamic equilibration in HIC will do
In practice, the choices we have are:
N=4 SYM at strong coupling via AdS/CFT; Problems: not QCD; validity at g~1?
PQCD (e.g. parton cascade); Problem: validity at g~1?
CGC/Plasma Inst.: via CYM/Boltzmann simulations; Problems: groups disagree on equilibration/validity at g~1?

5. AdS and CGC can be friends ;-)
I’ll talk about AdS/CFT as pre-eq model… ..but I really would like to see controlled pQCD/CGC results on <pT>, dN/dY and flow (even interesting for g<<1!) Reason: maybe by interpolating between controlled results at g2N->0 and g2N->∞ we could actually ‘bracket’ QCD at g2N~1.

6. AdS/CFT Strong Coupling Equilibrates naturally
Large Nc limit probably harmless as approximation to QCD
Conformal EoS: probably harmless as approximation to QCD for T>300 MeV
Conceptually clean model system
Numerically hard: real time 5d strong field gravity

7. AdS/CFT for HIC equilibration
Classical setup: treat HIC as shock-wave collision problem in 5d asymptotic Einstein GR
Many groups have worked on this, I will selfishly mostly report about our group’s effort (apologies)
One highlight: early-time energy density and flow from analytic calculation for central AA:
(also results for central pA in PR&Hogg 2013)
[Grumiller&PR 2008; PR & Hogg 2013]

8. Shock Wave Collisions in AdS5
Analytic solutions uncontrolled at finite time, would need to resum [Minwalla et al. , JHEP09]
Our solution: use analytic post-collision line element as initial conditions for full numerical GR solver
We are able to follow complete dynamics, including equilibration
After equilibration, Tab data can be fed into viscous hydro (AdS+hydro+cascade, “SONIC”)

9. Numerical BH equilibration in AdS5
[van der Schee, PR & Pratt, PRL111 (2013)]

10. AdS+hydro+cascade
[van der Schee, PR & Pratt, 2013]

11. AdS+hydro+cascade
[van der Schee, PR & Pratt, 2013]

12. AdS+hydro+cascade
AdS/CFT+hydro results are independent of choice of switching time
You get what you get. No ‘tuning’

13. Strong vs. Weak Coupling
[van der Schee, PR & Pratt, 2013]
[Epelbaum, Gelis, 2013]
How about making more comparisons like these???

14. Phenomenology from AdS/CFT
There is pre-equilibrium flow generated in early-time dynamics
We would like to calculate flow and more generally hydro initial conditions for lumpy AA and pA
Right now we can only do smooth, central AA (except , ask me if interested)
We’re going to model AdS/CFT pre-flow (but eventually will calculate it)

15. Pre-equilibrium flow (smooth AA)
[van der Schee, PR & Pratt, 2013]

16. SONIC (AA)
Idea: pre-equilibrium flow for smooth, central collisions is simple
Based on [PR & Hogg, 2013], parametrize as
and use for different collision systems (Pb+Pb, Au+Au, Cu+Cu, Al+Al, C+C, p+p)
Compare:
[Scott & Vredevoogd, PRC ]

17. [Habich, Nagle and PR, ]

18. SONIC: AdS+Hydro (eta/s=0.08)+Hadron Cascade
[Habich, Nagle and PR, ]

19. SONIC: AdS+Hydro (eta/s=0.08)+Hadron Cascade
[Habich, Nagle and PR, ]

20. SONIC: AdS+Hydro (eta/s=0.08)+Hadron Cascade
[Habich, Nagle and PR, ]

21. SONIC: AdS+Hydro (eta/s=0.08)+Hadron Cascade
[Habich, Nagle and PR, ]

22. SONIC: AdS+Hydro (eta/s=0.08)+Hadron Cascade
[Habich, Nagle and PR, ]

23. SONIC: AdS+Hydro (eta/s=0.08)+Hadron Cascade
[Habich, Nagle and PR, ]

24. Without tuning, SONIC offers good overall description of data in central AA
Full evolution info of T and v in central AA publicly available; you may use it for jet quenching, photons, heavy-quarks, …

25. More modelling: lumpy SONIC
Pocket formula
can be generalized to non-symmetric (lumpy) initial conditions; no more guidance from numerical GR, this is a pure model (for now)!

26. More modelling: lumpy SONIC
Pocket formula
can be generalized to non-symmetric (lumpy) initial conditions; no more guidance from numerical GR, this is a pure model (for now)!

27. More modelling: super!SONIC
Pocket formula
can be generalized to non-symmetric (lumpy) initial conditions; no more guidance from numerical GR, this is a pure model (for now)!

28. RHIC
[w/o preflow: Nagle et al, PRL 113 ( )]

29. RHIC
[w/o preflow: Nagle et al, PRL 113 ( )]

30. RHIC
[w/o preflow: Nagle et al, PRL 113 ( )]

31. RHIC
[w/o preflow: Nagle et al, PRL 113 ( )]

32. RHIC
[w/o preflow: Nagle et al, PRL 113 ( )]

33. Message: pre-equilibrium flow important for small system vn’s
RHIC
Originally, we predicted v3(2 GeV)~0.03 (no pre-equilibrium flow)
WITH preflow: v3(2GeV)~0.06
Message: pre-equilibrium flow important for small system vn’s

34. He3Au theory predictions vs data
Glauber+hydro+cascade
IP-Glasma+Music
(Glauber+AdS+hydro+cascade)
Glauber predictions (even w/o preflow) pretty good; don’t need IP-Glasma to describe He3-Au

35. How to make progress Is Saturation seen at RHIC/LHC?
Is Saturation NECESSARY to describe RHIC/LHC data?
My suggestion: let’s do a better job of describing ALL experimental data using Glauber (Glauber+super!SONIC)
If there are clear, unambiguous examples of data that cannot be described by Glauber (but by IP-Glasma) then we have ‘evidence’

36. Conclusions
More realistic and predictive HIC models need to include fully dynamical equilibration
I’ve presented work at strong coupling (AdS)
Dear weak coupling/CGC friends: let’s compare τhydro, <pT>! Let’s ‘bracket’ QCD!
Fully dynamical model SONIC (AdS+hydro+cascade): data/model comparison for spectra HBT in AA look pretty good
He3Au: I believe we originally underpredicted v3 by 50%; now (w/ preflow) v3(2 GeV)~0.06

37. Thank you for your attention!
Special thanks to my collaborators: A. Adare, H. Bantilan, S. Beckman, J. Carlson, M. Habich, T. Koblesky, J. Oruela Koop, J. Lynn, M. McCumber, D. McGlinchey, J. Nagle, S. Pratt, W. van der Schee

38. Bonus Material

40. Metric, separation D=0.7

41. [Bantilan and PR, ]

42. Glauber+hydro+cascade: dAu

43. Glauber+hydro+cascade: pPb