RELIC GRAVITATIONAL-WAVES FROM COSMIC STRINGS - UPDATED CONSTRAINTS AND OPPORTUNITIES FOR DETECTION

We examine the spectrum of gravitational radiation emitted by a networ k of cosmic strings, with emphasis on the observational constraints an d the opportunities for detection. The analysis improves over past wor k, as we use a phenomenological model for the radiation spectrum emitt ed by a cosmic string loop. This model attempts to include the effect of the gravitational back reaction on the radiation emission by an ind ividual loop with a high frequency cutoff in the spectrum. Comparison of the total spectrum due to a network of strings with the recently im proved bound on the amplitude of a stochastic gravitational wave backg round, due to measurements of noise in pulsar signal arrival times, al lows us to exclude a range of values of mu, the cosmic string linear m ass density, for certain values of cosmic string and cosmological para meters. We find the conservative bound G mu/c(2)<5.4(+/-1.1)X10(-6) wh ich is consistent with all other limits. We consider variations of the standard cosmological scenario, finding that an underdense, Omega(0)< 1 universe has little effect on the spectrum, whereas the portion of t he spectrum probed by gravitational wave detectors is strongly sensiti ve to the thermal history of the cosmological fluid. We discuss the op portunity for the observation of this stochastic background by resonan t mass and laser interferometer gravitational wave detectors.