Jet Quenching and Holographic Thermalization

Transcription

1 Jet Quenching and Holographic Thermalization Di-Lun Yang (Duke University) with Berndt Muller

2 Outline Energy loss in the holographic picture Thermalization and gravitational collapse : The falling mass shell in AdS-Vaidya spacetime Stopping diatance : Null geodesic of a massless particle moving in AdS-Vaidya spacetime Approximating jet quenching parameter : The moving string in AdS-Vaidya spacetime Summary

3 Energy loss of a heavy quark in N=4 SYM Trailing string : drag force and diffusion Lightcone Wilson loop : multiple scattering and momentum broadening The string profile can be obtained by extremized the Nambu- Goto action in AdS-Schwarzschild spacetime. By using Langevin equation, the drag coefficient can be derived. x 3 ( t, z) vt ( z) Gubser, Herzog et.al. Liu et.al. d() z v z 4 dz 1 ( z / zh) zh z z z / :causally disconnected v dp dt 2 3 YM c 2 p3 h g 2 N T m 2 dressed field radiation

4 Falling string and gluon energy loss The string with two ends attached to the branes below horizon may describe a gluon traveling in the medium. tip : null geodesic (trajectory of a massless particle) lower part: trailing string The string will eventually fall to the horizon longitudinal displacement : maximum stopping distance 1 1 p1/ p0 x zh dy y UV 1 (1 y ) p / p BDMPS formalism: 1 E C qˆ( x ) 4 s R 1 2 Gubser et.al. JHEP0810:052,2008

5 Gravitational collapse and the thermalization The stationary black hole can only describe the physics after the thermalization. Gravitation collapse : the formation of black hole corresponds to the thermalization of medium. Anisotropic and time-dependent metric on the boundary: radiation to the bulk and the formation of horizon. P. Chesler and L. Yaffe Different approach : Black hole formation as a shrinking shell?

6 Falling mass shell and AdS-Vaidya spacetime A light-like falling mass shell (shock wave) finally forms a black hole. V. Balasubramanian et.al. Phys.Rev.D84:026010,2011 Outside : AdS-Schwarzschild (thermalized medium) Inside : quasi-ads (vacuum) AdS-Vaidya spacetime: 1 ds (1 m( v) z ) dv 2dvdz dx z Thin shell limit: M v mv ( ) 1tanh 2 v 0 v dt dz 4 1 Mz dv c( z0) dt dz red shift v 0( z z ) if 0 if v 0( z z ) 0 Mz (2 Mz ) cz ( ) exp[ ] (1 Mz0 ) B. Muller QM2011

7 Derivation of the red shift factor Original metric: m( v) m( t, r) Generalization in AdS spacetime: ( R 1) where z=1/r m' m Finding and for the specific shell.

8 Derivation of the red shift factor Specific function of the sell: We derive Spacetime metric requires In the thin shell limit, by taking the expansion of zero of v Red shift factor

9 The Position of Shell Spacetimes in two regions: f 1 ( z / z h ) 4 The position of shell can be found by using The position of shell is a function of t. The shell coincides with the horizon at large t. Linear approximation leads to t0 1/ ( T ) t0 0.2 fm (e.g. T=300 MeV, ) inside outside horizon boundary mass shell zh ( T) z () t 0 z 1 t

10 Null geodesic in AdS-Vaidya spacetime A massless particle traveling in AdS-Vaidya spacetime follows the null geodesic, Ejecting a particle with 4-momentum 0,1, 2,3 Outside the shell(ads-schwarzschild spacetime): 1 dz ds f z dt dx z f () z () 2 P. Arnold and D. Vaman, JHEP 1104:027,2011 q Inside the shell(quasi-ads spacetime): 1 ds c( z ) dt dz dx z

11 Matching condition The energy defined in two spacetimes match at the collision point dt d dt d z z c c z f ( z ) z 2 1 c c 2 c when the collision point is not too close to the future horizon.

12 Longitudinal velocity of the almost onshell particle In AdSSS In qadss AdSSS qadss q 0.99 q 0.99 The particle ceases moving in both AdSSS and qadss, which leads to the maximum stopping distances.

13 Transverse velocities in the vicinity of shell What happen at the collision point? Comparing the transverse velocities dz/dt: z c q 0.6 q 0.99

14 Trajectory of the particle Assuming no interaction 1 st collision: outpaced by the shell 2 nd collision: accrete to the shell shell pt in qads pt in AdSSS For the particle ejected near the boundary, the result will be the same as that in pure AdSSS. q q 0.99 m z m z 0.6

15 Maximum stopping distance The maximum stopping distance : the longitudinal displacement from the starting point to the accretion point. In qadss: In pure AdSSS: x ( z z ) ( EL) x 3 1/2 s qads c m ( EL) 3 1/4 s AdSSS z 0.4 z 0.6 m q 0.99 q L & P. Arnold and D. Vaman, JHEP 1104:027,2011 m pt in AdS-Vaidya pt in AdSSS

16 Comparing stopping distances The particle will travel further in AdS-Vaidya than in AdSSS. When the starting point is close to the boundary, two results coincide. When the starting point is close to the future horizon, the particle will travel all the way in qadss. 3 x s AdS-Vaidya AdSSS shell pt in qads pt in AdSSS z q 0.99 q q zm x s t z m z

17 Falling String in AdS-Vaidya spacetime All pieces of the straight string may move parallely along the null geodesic in qadss. When the string penetrates the shell, the tip of the string may still move along the null geodesic. The rest part outside the shell will be trailed, while the part inside the shell will remain straight.

18 Set up the initial condition of string 3 The string move with a constant velocity along x in qadss. Setting x 3 ( t, z) vt Momentum density: All pieces move along the null geodesic: For an observer at the boundary, the energy varies with time. Same results can be obtained by taking the trailing string profile and setting and substituting with. zh t t Compared with trailing string profile in AdSSS: Gubser et.al. JHEP0810:052,2008

19 Computing the jet quenching parameter BDMPS formalism: ˆq in AdS-Vaidya and in pure AdSSS coincide at the UV limit. Obvious scheme:, Alternative scheme:, (S. Gubser, Phys.Rev.D76:126003,2007) q 0.99, v 0.99 AdSSS AdS-Vaidya RHIC data: 2 qˆ 2 10( GeV / fm) at T=400 MeV S. A. Bass et.al. Phys.Rev.C 79: (2009)

20 Summary We have written down the Vaidya metric in the thin shell limit and approximated the thermal equilibration time. A massless particle moving along the null geodesics results in larger stopping distance in AdS-Vaidya spacetime. We found a distinct scenario of a falling string in the thermalization process. By applying BDMPS formalism, we obtained smaller. Caveats : N=4 SYM is distinct from QCD. The correspondence of non-local objects and physics in gauge theory side may be obscure. However, we are probably in the ballpark! ˆq

21 Thank you!

22 Dangling string and wave velocity Nambu-Goto action in qadss: Taking and finding the EOM of L v 0.99 v 0.1 v shell v wave