Bulk viscosity effects in event-by-event relativistic hydrodynamics

Abstract

Bulk viscosity effects on the collective flow harmonics in heavy ion collisions are investigated, on an event by event basis, using a newly developed 2+1 Lagrangian hydrodynamic code named v-USPhydro which implements the Smoothed Particle Hydrodynamics (SPH) algorithm for viscous hydrodynamics. A new formula for the bulk viscous corrections present in the distribution function at freeze-out is derived starting from the Boltzmann equation for multi-hadron species. Bulk viscosity is shown to enhance the collective flow Fourier coefficients from v2(pT ) to v5(pT ) when pT ∼ 1 − 3 GeV even when the bulk viscosity to entropy density ratio, ζ/s, is significantly smaller than 1/(4π).

Event-by-EventHydrodynamics+JetEnergy Loss: A Solution to theRAA⊗vNoronha-Hostler1, Betz2, Noronha3 et al. 2016Phys. Rev. Lett.Self Cite11761573View full textAdd to dashboardCite

“…The soft sector is modeled via event-by-event hydrodynamic simulations performed using the v-USPhydro code [61][62][63][64] while the hard sector is described using the energy loss framework developed in [36,65,66]. We show that the positive contribution from low p T v 2 fluctuations overwhelms the small, negative contributions from event plane fluctuations, which in turn leads to an overall enhancement of high p T elliptic flow in comparison to previous calculations.…”

“…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. The initial time for all the hydrodynamic simulations was 0.6 fm and we used the lattice-based equation of state EOS S95n-v1 [77] and an isothermal Cooper-Frye [78] freezeout with freeze-out temperature T F = 120 MeV for MCKLN and T F = 130 for MCGlauber.…”

“…Hydrodynamic evolution. The expanding QGP is modeled through event-by-event simulations performed using the 2+1 (i.e., boost invariant) viscous relativistic hydrodynamics code called v-USPhydro [61][62][63][64]. vUSPhydro accurately [68] solves the energy-momentum conservation equations and the equations of motion for the dissipative currents using the Lagrangian formulation of hydrodynamics encoded in the Smoothed Particle Hydrodynamics (SPH) algorithm [69,70].…”

Temperature dependent transport coefficients in a dynamical holographic QCD model

“…The near phase transition enhancement of bulk viscosity corresponds to the peak of trace anomaly around T c , which shows the equation of state is highly nonconformal [36,37] around phase transition. Recent studies [38,39] show that bulk viscosity could also have important effects on hydrodynamic simulations of HIC: it would increase the flow harmonics(such as v 2 and v 3 ) while shear viscosity decreases them.…”

Nonlinear waves in second order conformal hydrodynamics

“…Effects from bulk viscosity (see, for instance, [41,42]) or from additional conserved charges are not taken into account here. Furthermore, even though the equation of motion for π µν derived from kinetic theory contains many more terms than the ones used here [43], in this paper we shall focus on the simplest set of equations that can still describe a causal (and stable) conformal dissipative fluid.…”