  Elastic radial deformation of multiwall carbon nanotubes (MWNTs) under
hydrostatic pressure is investigated within the continuum elastic
approximation. The thin-shell theory, with accurate elastic constants and
interwall couplings, allows us to estimate the critical pressure $p_c$ above
which the original circular cross-section transforms into radially corrugated
ones. Emphasis is placed on the rigorous formulation of the van der Waals
interaction between adjacent walls, which we analyze using two different
approaches. Possible consequences of the radial corrugation in the physical
properties of pressurized MWNTs are also discussed.
