Scaling configurations of cosmic superstring networks and their cosmological implications

Abstract

We study the cosmic microwave background temperature and polarization spectra sourced by multitension cosmic-superstring networks. First, we obtain solutions for the characteristic length scales and velocities associated with the evolution of a network of F-D strings, allowing for the formation of junctions between strings of different tensions. We find two distinct regimes describing the resulting scaling distributions for the relative densities of the different types of strings, depending on the magnitude of the fundamental string coupling ${g}_{s}$. In one of them, corresponding to the value of the coupling being of order unity, the network's stress-energy power spectrum is dominated by populous light F and D strings, while the other regime, at smaller values of ${g}_{s}$, has the spectrum dominated by rare heavy D strings. These regimes are seen in the cosmic microwave background (CMB) anisotropies associated with the network. We focus on the dependence of the shape of the B-mode polarization spectrum on ${g}_{s}$ and show that measuring the peak position of the B-mode spectrum can point to a particular value of the string coupling. Finally, we assess how this result, along with pulsar bounds on the production of gravitational waves from strings, can be used to constrain a combination of ${g}_{s}$ and the fundamental string tension ${\ensuremath{\mu}}_{F}$. Since CMB and pulsar bounds constrain different combinations of the string tensions and densities, they result in distinct shapes of bounding contours in the $({\ensuremath{\mu}}_{F},{g}_{s})$ parameter plane, thus providing complementary constraints on the properties of cosmic superstrings.