Gravitational radiation dominated cosmologies

Robertson-Walker cosmologies with matter, radiation, and nonzero cosmological constant are examined to determine how much high-frequency gravitational radiation may be present at the current epoch without violating observations. Evolutionary limits due to a maximum redshift requirement, minimum age requirement, and magnitude-redshift relation are used to rule out most M2 models and to restrict singular models to those satisfying an acceleration parameter limit of -4.4-5.6, a matter density limit of less than 4.7, and a radiation density limit of less than 3.4. These limits are compared to direct limits from various experimental searches for a cosmic gravitational radiation background; it is found that several experiments are very close to a significant sensitivity.