  Inflation generates gravitational waves, which may be observable in the low
multipoles of the cosmic microwave background (cmb) anisotropy but only if the
inflaton field variation is at least of order the Planck scale. Such a large
variation would imply that the model of inflation cannot be part of an ordinary
extension of the standard model, and combined with the detection of the waves
it would also suggest that the inflaton field cannot be one of the superstring
moduli. Another implication of observable gravitational waves would be a
potential $V^{1/4}=2$ to $4\times 10^{16}\GeV$, which is orders of magnitude
bigger than is expected on the basis of particle theory. It might emerge in a
hybrid inflation model where most of the energy density comes from the Higgs
sector of a GUT, but only if both the vacuum expectation values {\em and the
masses } of the Higgs fields are of this order.
