Grand unification, gravitational waves, and the cosmic microwave background anisotropy

We reexamine the stochastic gravitational wave background resulting from inflation and its effect on the cosmic microwave background radiation (CMBR). Measurement by the Cosmic Background Explorer satellite of a CMBR quadrupole anisotropy places an upper limit on the vacuum energy during inflation of ≊5×${10}^{16}$ GeV. Gravitational waves from inflation could produce the entire observed signal if the vacuum energy during inflation was as small as 1.5×${10}^{16}$ GeV at the 95% confidence level. This coincides with recent estimates of grand unification scales inferred from renormalization-group arguments, for Supersymmetric grand unified theories. Further tests of this possibility are examined, based on analyzing the energy density associated with gravitational waves from inflation.