Weakly nonlinear theory of pattern-forming systems with spontaneously broken isotropy

Quasi-two-dimensional pattern-forming systems with spontaneously broken isotropy represent a novel symmetry class, that is, experimentally accessible in electroconvection of homeotropically aligned liquid crystals. We present a weakly nonlinear analysis leading to amplitude equations which couple the short-wavelength patterning mode with the Goldstone mode resulting from the broken isotropy. The new coefficients in these equations are calculated from the hydrodynamics. Simulations exhibit a new type of spatiotemporal chaos at onset. The results are compared with experiments.