Constraints on the fundamental string coupling from B-mode experiments
  We study signatures of cosmic superstring networks containing strings of
multiple tensions and Y-junctions, on the cosmic microwave background (CMB)
temperature and polarisation spectra. Focusing on the crucial role of the
string coupling constant $g_s$, we show that the number density and energy
density of the scaling network are dominated by different types of string in
the $g_s \sim 1$ and $g_s \ll 1$ limits. This can lead to an observable shift
in the position of the B-mode peak --- a distinct signal leading to a direct
constraint on $g_s$. We forecast the joint bounds on $g_s$ and the fundamental
string tension $\mu_F$ from upcoming and future CMB polarisation experiments,
as well as the signal to noise in detecting the difference between B-mode
signals in the limiting cases of large and small $g_s$. We show that such a
detectable shift is within reach of planned experiments.
