Gravitational Waves from Light Cosmic Strings: Backgrounds and Bursts with Large Loops

Abstract

The mean spectrum and burst statistics of gravitational waves produced by a cosmological population of cosmic string loops are estimated using analytic approximations, calibrated with earlier simulations. Formulas are derived showing the dependence of observables on the string tension, in the regime where newly-formed loops are relatively large, not very much smaller than the horizon. Large loops form earlier, are more abundant, and generate a more intense stochastic background and more frequent bursts than assumed in earlier background estimates, enabling experiments to probe lighter cosmic strings of interest to string theory. Predictions are compared with instrument noise from current and future experiments, and with confusion noise from known astrophysical gravitational wave sources such as stellar and massive black hole binaries. In these large-loop models, current data from millisecond pulsar timing already suggests that the tension is less than about $10^{-10}$, a typical value expected in strings from brane inflation. LISA will be sensitive to stochastic backgrounds created by strings as light as $G\mu \approx 10^{-15}$, at frequencies where it is limited by confusion noise of Galactic stellar populations; however, for those lightest detectable strings, bursts are rarely detectable.

22 pages, Latex, 1 figure, submitted to Phys Rev D; minor corrections and clarifications added

References in corpus (1)

• Gravitational wave bursts from cosmic (super)strings: Quantitative analysis and constraints

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• Periodic Gravitational Waves From Small Cosmic String Loops
• Clustering of Superstring Loops
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