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Abstract:
We examine whether cubic nonlinearities, allowed by symmetry in the elastic energy of a contact line, may result in a different universality class at depinning. Standard linear elasticity predicts a roughness exponent ζ=1/3(one loop), ζ=0.388±0.002(numerics) while experiments give ζ 0.5. Within functional renormalization group methods we find that a nonlocal Kardar-Parisi-Zhang-type term is generated at depinning and grows under coarse graining. A fixed point with ζ 0.45(one loop) is identified, showing that large enough cubic terms increase the roughness. This fixed point is unstable, revealing a rough strong-coupling phase. Experimental study of contact angles θ near π/2, where cubic terms in the energy vanish, is suggested. © 2006 The American Physical Society.
