Constraints on Cosmic Strings from the LIGO-Virgo Gravitational Wave Detectors

Cosmic strings can give rise to a large variety of interesting astrophysical phenomena. Among them, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observational signature. In this Letter we present a search for GWs from cosmic string cusps in data collected by the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days of live time. We find no evidence of GW signals from cosmic strings. From this result, we derive new constraints on cosmic string parameters, which complement and improve existing limits from previous searches for a stochastic background of GWs from cosmic microwave background measurements and pulsar timing data. In particular, if the size of loops is given by the gravitational backreaction scale, we place upper limits on the string tension Gµ below 10 −8 in some regions of the cosmic string parameter space. Introduction. A cosmic network of strings may form as a result of phase transitions in the early Universe [1]. When a U(1) symmetry is broken in multiple causally disconnected spacetime regions, one-dimensional topo-logical defects, i.e., strings, are expected to form [2]. For a long time, cosmic strings were considered candidate sources for structure formation in the early Universe [3]. Cosmic microwave background (CMB) experiments , however, have shown that cosmic strings can only contribute up to a few percent of the overall anisotropies observed [4–8]. More recently it was realized that strings can also be produced within the framework of string theory inspired cosmological models and grow to cosmic scales [9–13]. Cosmic strings produced in string theory motivated models (dubbed " cosmic superstrings ") have received much attention since they could provide observational signatures of string theory [14, 15].