Hadron mass spectrum and the shear viscosity to entropy density ratio of hot hadronic matter

Abstract

2012Hadron mass spectrum and the shear viscosity to entropy density ratio of hot hadronic matter PHYSICAL REVIEW C, COLLEGE PK, v. 86, pp. 751-766, AUG 27, 2012 Lattice calculations of the QCD trace anomaly at temperatures T < 160 MeV have been shown to match hadron resonance gas model calculations, which include an exponentially rising hadron mass spectrum. In this paper we perform a more detailed comparison of the model calculations to lattice data that confirms the need for an exponentially increasing density of hadronic states. Also, we find that the lattice data is compatible with a hadron density of states that goes as ρ(m) ∼ m −a exp(m/T H ) at large m with a > 5/2 (where T H ∼ 167 MeV). With this specific subleading contribution to the density of states, heavy resonances are most likely to undergo two-body decay (instead of multiparticle decay), which facilitates their inclusion into hadron transport codes. Moreover, estimates for the shear viscosity and the shear relaxation time coefficient of the hadron resonance model computed within the excluded volume approximation suggest that these transport coefficients are sensitive to the parameters that define the hadron mass spectrum.

Bulk and shear viscosities of hot and dense hadron gas

“…(10) gives good fit to lattice data up to 150M eV even at µ = 300M eV reasonably well. We have taken a higher T H value compared to [20] that was required to fit the lattice data [39]. This is because, in Ref.…”

“…Within the hadron resonance model, the attractive channels are effectively included by including the resonances and the repulsive channels can be modeled in a simple manner through and excluded volume correction [28][29][30]. The shear viscosity in a relativistic gas of multi component hard core spheres can be written as [17,20] …”

“…Such a description could describe the lattice data and indicated that the hadronic matter could become almost a perfect fluid where η s could approach the KKS bound. Later lattice data [6] which indicated a lower pseudocritical temperature about 160 MeV led to the assertion that the hot hadronic matter described through hadron resonance gas is far from being a perfect fluid [20]. All these studies have been done at zero baryon density.…”

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“…Information about four transport coe cients is required: the temperature-dependent shear and bulk viscosities, ⌘ and ⇣, and their respective relaxation time coe cients, ⌧ ⇡ and ⌧ ⇧ (other 2nd order transport coe cients [71] are not yet taken into account). For simplicity, e↵ects from the temperature dependence of ⌘/s in the hadronic [72][73][74] or in the QGP phase [75] are neglected here and, thus, we set ⌘/s to be a constant. Also, in this first study bulk viscosity [61,62,76] is set to zero.…”

Nonlinear waves in second order conformal hydrodynamics

“…In contrast, at low temperatures and nonzero baryon chemical potentials in the hadron gas phase, viscous effects may be considerably more pronounced [4][5][6][7][8]. Numerical studies of the hydrodynamical evolution of the QuarkGluon Plasma (QGP) show that viscosity produces some visible but not very large effects on global observables [9].…”