Abstract
We analyse by field theoretical methods the large scale behavior of a stack of tethered or polymerized membranes. We show that, in the decoupled phase where there is no resistance to the shear between successive membranes, anharmonic terms dictated by rotational symmetry in the bulk have to be taken into account. They renormalize the elastic coefficients and lead to a large distance anomalous elasticity, as in the case of a single tethered membrane