Strong fluctuations in the relaxation of a 2D granular fluid

Horacio Castillo, Department of Physics and Astronomy, Ohio University

Glass transitions are associated with a rapid increase of the

relaxation time in a system as a function of an external parameter,

usually temperature or volume fraction. In the regime near the glass

transition, materials exhibit “dynamical heterogeneity”, i.e., the

presence of correlated fluctuations in the dynamical behavior of small

regions of the system, whose origin is still poorly understood. I will

discuss the results of large-scale numerical simulations of a two

dimensional granular fluid, for different strengths of the dissipation

in the system (described by the restitution coefficient ε), including

the case of no dissipation (ε=1). I will focus on the behavior of the

system for packing fractions near structural arrest. In that regime,

the correlation length achieves values that widely exceed those

previously observed for 3D hard sphere fluids, the correlation

functions exhibit a very good scaling when the wavevector is rescaled

by the correlation length, and this scaling is remarkably independent

of ε. I will discuss two alternative descriptions of the geometry of

the correlated regions. One is based on studying the scaling of the

dynamic susceptibility, which provides a rough measure of the volume

of the correlated regions, with the correlation length. The other is

based on studying the statistics of clusters of slow and fast

particles, their volumes, and their radius of gyration. Taken

together, the results suggest that, even though the strength of the

fluctuations depends strongly on the intensity of the dissipation in

the system, the qualitative properties of the glass transition are

essentially independent of it.

Host: Philip Taylor