Gravitational instabilities in helicity-1 waves propagating through matterin equilibrium

It is shown that the interaction of helicity-1 waves of gravity and matter in a thin slab configuration produces new types of instabilities. Indeed, a spin-2 helicity-1 mode interacts strongly with the shear motion of matter. This mode is unstable above a critical wavelength, lambda(c) = root pi c(2 )/2G rho This should be compared with Jeans wavelength, lambda(J) = root pi c(s)(2)/G rho where c(s) is the sound speed. The two instabilities are of course different. For the case analysed, a plane parallel configuration, Je ans instability appears through a density wave perturbation, the material c ollapsing into a set of plane-parallel slabs. On the other hand, the helici ty-1 wave instability induces a transverse motion in the fluid that tends t o shear in the material along the node of the perturbation.