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Inflation predicts a primordial gravitational wave spectrum that is slightly``red,'' i.e., nearly scale-invariant with slowly increasing power at longerwavelengths. In this paper, we compute both the amplitude and spectral form ofthe primordial tensor spectrum predicted by cyclic/ekpyrotic models. Thespectrum is blue and exponentially suppressed compared to inflation on longwavelengths. The strongest observational constraint emerges from therequirement that the energy density in gravitational waves should not exceedaround 10 per cent of the energy density at the time of nucleosynthesis.Comment: 4 pages, 3 figuer

Cosmic gravitational-wave background in a cyclic universe