Shear viscosity of a hadron gas and influence of resonance lifetimes on relaxation time

We address a discrepancy between different computations of η/s (shear viscosity over entropy density) of hadronic matter. Substantial deviations of this coefficient are found between transport approaches mainly based on resonance propagation with finite lifetime and other (semianalytical) approaches with energy-dependent cross sections, where interactions do not introduce a timescale. We provide an independent extraction of this coefficient by using the newly developed SMASH (Simulating Many Accelerated Strongly interacting Hadrons) transport code, which is an example of a mainly resonance-based approach. We compare the results from SMASH with numerical solutions of the Boltzmann equation for simple systems using the Chapman-Enskog expansion, as well as previous results in the literature. Our conclusion is that the hadron interaction via resonance formation/decay strongly affects the transport properties of the system, resulting in significant differences in η/s with respect to other approaches where binary collisions dominate. We argue that the relaxation time of the system—which characterizes the shear viscosity—is determined by the interplay between the mean free time and the lifetime of resonances. We show how an artificial shortening of the resonance lifetimes, or the addition of a background elastic cross section nicely interpolate between the two discrepant results.

Note:

15 pages, 16 figures

resonance: lifetime
hadron: gas
cross section: energy dependence
matter: hadronic
viscosity: density
entropy: density
density: ratio
potential: chemical
resonance: decay
Boltzmann equation

References(68)

Figures(25)

[1]

Course of Theoretical Physics Vol.10: Physical Kinetics

E.M. Lifschitz
,
L.P. Pitaevskii

[2]

Relativistic Kinetic Theory: Principles and Applications

S.R. De Groot
,
W.A. van Leeuwen
,
C.G. van Weert

[3]

Anisotropic transverse flow and the quark hadron phase transition

Peter F. Kolb
(
- CERN and
- Regensburg U.
)
,
Josef Sollfrank
(
- Regensburg U.
)
,
Ulrich W. Heinz
(
- CERN
)

- Phys.Rev.C 62 (2000) 054909
•
e-Print:
- hep-ph/0006129
•
DOI:
- 10.1103/PhysRevC.62.054909

[4]

Radial and elliptic flow at RHIC: Further predictions

P. Huovinen
(
- LBL, Berkeley
)
,
P.F. Kolb
(
- Ohio State U. and
- Regensburg U.
)
,
Ulrich W. Heinz
(
- Ohio State U.
)
,
P.V. Ruuskanen
(
- Jyvaskyla U.
)
,
S.A. Voloshin
(
- Wayne State U.
)

- Phys.Lett.B 503 (2001) 58-64
•
e-Print:
- hep-ph/0101136
•
DOI:
- 10.1016/S0370-2693(01)00219-2

[5]

Holography and hydrodynamics: Diffusion on stretched horizons

- JHEP 10 (2003) 064
•
e-Print:
- hep-th/0309213
•
DOI:
- 10.1088/1126-6708/2003/10/064

[6]

Viscosity in strongly interacting quantum field theories from black hole physics

- Phys.Rev.Lett. 94 (2005) 111601
•
e-Print:
- hep-th/0405231
•
DOI:
- 10.1103/PhysRevLett.94.111601

[7]

Viscosity Information from Relativistic Nuclear Collisions: How Perfect is the Fluid Observed at RHIC?

- Phys.Rev.Lett. 99 (2007) 172301
•
e-Print:
- 0706.1522
•
DOI:
- 10.1103/PhysRevLett.99.172301

[8]

Simulating elliptic flow with viscous hydrodynamics

K. Dusling
(
- SUNY, Stony Brook
)
,
D. Teaney
(
- SUNY, Stony Brook
)

- Phys.Rev.C 77 (2008) 034905
•
e-Print:
- 0710.5932
•
DOI:
- 10.1103/PhysRevC.77.034905

[9]

Dissipative Phenomena in Quark Gluon Plasmas

P. Danielewicz
(
- LBL, Berkeley
)
,
M. Gyulassy
(
- LBL, Berkeley
)

- Phys.Rev.D 31 (1985) 53-62,
- Lawrence Berkeley Lab. - LBL-17278 (84,REC.JUN.) 34p,
- Phys. Rev. D31 ( 1985) 53-62 and Lawrence Berkeley Lab. - LBL-17278 (84,REC.JUN.) 34p
•
DOI:
- 10.1103/PhysRevD.31.53