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Proceedings Paper

Lattice statistics studies of massless phases
Author(s): Ian G. Enting
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Paper Abstract

Many important concepts used in the study of complex systems have their origin in the lattice statistical mechanics of cooperative phase transitions. The classic order-disorder transitions of Potts/Ising models illustrate emergent phenomena such as spontaneous symmetry breaking, scale-free critical behaviour and power-law singularities. However, a class of lattice statistics models show that rather more complex behaviour can be obtained, under conditions which are suffciently general that they might also occur in less idealised models. A 5-state lattice statistics model is analysed to explore behaviour in and around a so-called "massless phase". The massless phase, characterised by power law decay of correlations, appears as an intermediate regime between high temperature disorder and low-temperature ordering. The critical exponents (and fractal spatial distributions) occur over a finite range of temperatures. The state of the massless phase is characterised by a topological ordering with analogues of spin-waves being the dominant perturbations. The transition from the ordered to massless phases is analysed using new exact series expansions obtained by the finite lattice method. The results are also compared to Monte Carlo simulations. The results are compared to other studies in the small number of cases where such series expansions exist for comparable models, including the 6-state "clock model". One of the properties that makes the massless phase dificult to study is the weak nature of the associated Kosterlitz-Thouless transition with exponentially-weak behaviour rather than power-law behaviour. As a further diffculty, the limiting behaviour is confined to a narrow regime, outside which one sees an apparent "cross-over" to power law behaviour. This suggests that behaviour analogous to the "massless phases" will be diffcult to characterise as one moves beyond idealised lattice systems.

Paper Details

Date Published: 5 January 2008
PDF: 10 pages
Proc. SPIE 6802, Complex Systems II, 68020L (5 January 2008);
Show Author Affiliations
Ian G. Enting, The Univ. of Melbourne (Australia)

Published in SPIE Proceedings Vol. 6802:
Complex Systems II
Derek Abbott; Tomaso Aste; Murray Batchelor; Robert Dewar; Tiziana Di Matteo; Tony Guttmann, Editor(s)

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