Probing Cosmic Superstrings with Gravitational Waves
  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 $G\mu_F<3.2 \times 10^{-9}$ 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 $G\mu_F$. We show that the inclusion of heavier string types is required for
a more accurate characterization of the region of the $(g_s,G\mu_F)$ 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.
