On the number of cosmic strings

The number of cosmic strings in the observable Universe is relevant in determining the probability of detecting such cosmic defects through their gravitational signatures. In particular, we refer to the observation of gravitational lensing events and anisotropy in the cosmic microwave background (CMB) radiation induced by cosmic strings. In this article, a simple method is adopted to obtain an approximate estimate of the number of segments of cosmic strings crossing the particle horizon that fall inside the observed part of the Universe. We show that there is an appreciable difference in the expected number of segments that differentiates cosmic strings arising in Abelian Higgs and Nambu–Goto models and that a different choice of setting for the cosmological model can lead to significant differences in the expected number of cosmic string segments. Of this number, the fraction that are realistically detectable may be considerably smaller