title: Hydrodynamic correlation functions of a driven granular fluid in steady state.
abstract: We study a homogeneously driven granular fluid of hard spheres at intermediate volume fractions and focus on time-delayed correlation functions in the stationary state. Inelastic collisions are modeled by incomplete normal restitution, allowing for efficient simulations with an event-driven algorithm. The incoherent scattering function F(incoh)(q,t) is seen to follow time-density superposition with a relaxation time that increases significantly as the volume fraction increases. The statistics of particle displacements is approximately Gaussian. For the coherent scattering function S(q,ω), we compare our results to the predictions of generalized fluctuating hydrodynamics, which takes into account that temperature fluctuations decay either diffusively or with a finite relaxation rate, depending on wave number and inelasticity. For sufficiently small wave number q we observe sound waves in the coherent scattering function S(q,ω) and the longitudinal current correlation function C(l)(q,ω). We determine the speed of sound and the transport coefficients and compare them to the results of kinetic theory.
authors.affiliation: Department of Physics and Astronomy, Bucknell University, Lewisburg, Pennsylvania 17837, USA. kvollmay@bucknell.edu
authors.forename: Katharina
authors.initials: K
authors.lastname: Vollmayr-Lee
authors.forename: Timo
authors.initials: T
authors.lastname: Aspelmeier
authors.forename: Annette
authors.initials: A
authors.lastname: Zippelius