Berlin 2008 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 14: Statistical physics II (general)

DY 14.2: Vortrag

Dienstag, 26. Februar 2008, 14:30–14:45, MA 004

Memory effects in the particles’ clustering in the Mean Field Hamiltonian model — •Angelo Facchini¹, Hiroko Koyama², and Stefano Ruffo³ — ¹Center for the Study of Complex Systems, University of Siena, Italy — ²Department of Physics, Nagoya University, Nagoya 464-8602, Japan — ³Dipartimento di Energetica ”S. Stecco”, University of Florence, INFN and CSDC, Italy

We investigate the memory effects in the dynamics of cluster in the Hamiltonian Mean Field model. In a preliminary paper, Koyama and Ruffo found that the life times, i.e. the time interval for which all the particles are trapped in the cluster, were distributed according to a power law. Here we extend this preliminar result investigating the power law distribution for energies ranging from U=0.3 to U=0.65 and particle number N=8,16,32,64,128,256,512. For a given N, we have computed the scaling index of the life-time distribution at different energies, showing that the phenomenon depends on both N and U. Furthermore, for a fixed N, Ruffo and Antoni [PRE,52,2361, 1995] showed that in the interval U=0−0.75, there is a specific value, U=0.3, for which the cluster begins to melt. Increasing U, the cluster continues to melt and the liquid phase disappears for U_c=0.75, the critical transition energy. By means of simulations in the microcanonical ensemble, we show that in the interval U=0.3−0.75, there is an energy range 0.3−U_pl for which the power law exists.

We show that this is a non thermodynamic effect, retraceble in the dynamics of the long range interaction between a small number of particles.