Probing cosmic superstrings with gravitational waves

Abstract

We compute the stochastic gravitational wave background generated by cosmic superstrings using a semi-analytical velocity-dependent model to describe their dynamics. We show that heavier string types may leave distinctive signatures on the stochastic gravitational wave background spectrum within the reach of present and upcoming gravitational wave detectors. We examine the physically motivated scenario in which the physical size of loops is determined by the gravitational backreaction scale and use NANOGRAV data to derive a conservative constraint of GµF < 3.2 × 10 −9 on the tension of fundamental strings. We demonstrate that approximating the gravitational wave spectrum generated by cosmic superstring networks using the spectrum generated by ordinary cosmic strings with reduced intercommuting probability (which is often done in the literature) leads, in general, to weaker observational constraints on GµF . We show that the inclusion of heavier string types is required for a more accurate characterization of the region of the (gs, GµF ) parameter space that may be probed using direct gravitational wave detectors. In particular, we consider the observational constraints that result from NANOGRAV data and show that heavier strings generate a secondary exclusion region of parameter space.

Probing the early Universe with axion physics and gravitational waves

“…where n ( , t) is the number density of loops of size i in the interval d , which receives contributions from all preexisting loops that have shrunk to the physical lengths (t ) at time t as [52,226,230,231] n ( , t) = ξ α a(t i ) a(t )…”

Energy-conservation constraints on cosmic string loop production and distribution functions

“…The maximum error they could have introduced is less than 1%. 6 Reference [15] defined scaling quantities in terms of the horizon distance and consequently the B found there was larger by factor (1 − ν) −3 . See the appendix.…”

“…Gravitational waves are the leading way to look for a cosmic string network [3][4][5][6][7][8][9][10][11][12]. The observable gravitational waves come mostly from the loop distribution, and therefore it is of great importance to understand this distribution.…”

Stochastic gravitational waves from cosmic string loops in scaling

“…[26,27]. However, most of the works having estimated the stochastic gravitational wave spectrum from loops have assumed utterly simplified loop distribution, or loop production function, usually postulated to be a Dirac function peaked at a length equal to some given fraction of the horizon size [28][29][30][31][32][33][34][35][36]. In the meanwhile, more recent Nambu-Goto simulations presented in Ref.…”