Gravitational wave bursts from cusps and kinks on cosmic strings - art. no. 064008

The strong beams of high-frequency gravitational waves (GW's) emitted by cu sps and kinks of cosmic strings are studied in detail. As a consequence of these beams, the stochastic ensemble of GW's generated by a cosmological ne twork of oscillating loops is strongly non-Gaussian, and includes occasiona l sharp bursts that stand above the "confusion" GW noise made of many small er overlapping bursts. Even if only 10% of all string loops have cusps thes e bursts might be detectable by the planned GW detectors Laser Interferomet ric Gravitation Observatory (LIGO)-VIRGO and Laser Interference Space Anten na (LISA) for string tensions as small as G mu similar to 10(-13). In the i mplausible case where the average cusp number per loop oscillation is extre mely small, the smaller bursts emitted by the ubiquitous kinks will be dete ctable by LISA for string tensions as small as G mu similar to 10(-12). We show that the strongly non-Gaussian nature of the stochastic GWs generated by strings modifies the usual derivation of constraints on G mu from pulsar timing experiments. In particular the Usually considered "rms GW backgroun d" is, when G mu less than or similar to 10(-7), an overestimate of the mor e relevant confusion GW noise because it includes rare, intense bursts. The consideration of the confusion GW noise suggests that a grand unified theo ry value G mu similar to 10(-6) is compatible with existing pulsar data, an d that a modest improvement in pulsar timing accuracy could detect the conf usion noise coming from a network of cuspy string loops down to G mu simila r to 10(-11). The GW bursts discussed here might be accompanied by gamma ra y bursts.