WEAKLY NONLINEAR-THEORY OF PATTERN-FORMING SYSTEMS WITH SPONTANEOUSLYBROKEN ISOTROPY

Quasi-two-dimensional pattern-forming systems with spontaneously broke n isotropy represent a novel symmetry class, that is, experimentally a ccessible in electroconvection of homeotropically aligned liquid cryst als. We present a weakly nonlinear analysis leading to amplitude equat ions which couple the short-wavelength patterning mode with the Goldst one mode resulting from the broken isotropy. The new coefficients in t hese equations are calculated from the hydrodynamics. Simulations exhi bit a new type of spatiotemporal chaos at onset. The results are compa red with experiments.