Detection of Low Tension Cosmic Superstrings

Abstract

Cosmic superstrings of string theory differ from conventional cosmic strings of field theory. We review how the physical and cosmological properties of the macroscopic string loops influence experimental searches for these relics from the epoch of inflation. The universe's average density of cosmic superstrings can easily exceed that of conventional cosmic strings having the same tension by two or more orders of magnitude. The cosmological behavior of the remnant superstring loops is qualitatively distinct because the string tension is exponentially smaller than the string scale in flux compactifications in string theory. Low tension superstring loops live longer, experience less recoil (rocket effect from the emission of gravitational radiation) and tend to cluster like dark matter in galaxies. Clustering enhances the string loop density with respect to the cosmological average in collapsed structures in the universe. The enhancement at the Sun's position is $\sim 10^5$. We develop a model encapsulating the leading order string theory effects, the current understanding of the string network loop production and the influence of cosmological structure formation suitable for forecasting the detection of superstring loops via optical microlensing, gravitational wave bursts and fast radio bursts. We evaluate the detection rate of bursts from cusps and kinks by LIGO- and LISA-like experiments. Clustering dominates rates for $G μ< 10^{-11.9}$ (LIGO cusp), $G μ<10^{-11.2}$ (LISA cusp), $G μ< 10^{-10.6}$ (LISA kink); we forecast experimentally accessible gravitational wave bursts for $G μ>10^{-14.2}$ (LIGO cusp), $G μ>10^{-15}$ (LISA cusp) and $G μ>10^{- 14.1}$ (LISA kink).