On the spontaneous symmetry breaking in the mesophases of achiral banana-shaped molecules

We propose that the natural tendency of banana-shaped mesogen molecules to induce a local bend of the nematic director can result in pathological elas ticity, with negative bend elastic constant. Under this hypothesis, a simpl e Landau-like phenomenological model predicts a symmetry-breaking transitio n inside the nematic phase, from uniform textures toward spontaneous period ic distortion, either oscillating splay-bend or conical twist-bend helix. T he predicted lower symmetry nematic phases are expected to show interesting polar properties, similar to those already reported for banana-shaped smec togens.