Cosmic Superstrings Revisited

TL;DR

This work revisits cosmic strings in string theory, arguing that warped compactifications and brane inflation can yield cosmic superstrings with tensions $G\mu$ spanning $10^{-12}$ to $10^{-6}$, while remaining observationally viable. It analyzes production mechanisms (brane–antibrane annihilation yielding F- and D-strings), stability (warping, throat localization, and discrete charges), and observational prospects across CMB, pulsars, lensing, and gravitational waves. A key contribution is identifying distinguishing features such as reconnection probability $P \sim g_s^2$ and a $(p,q)$ bound-state tension spectrum $\mu = \mu_0\sqrt{p^2 + q^2/g_s^2}$, with potential non-scaling networks that could reveal string theory in the sky. The paper emphasizes that, despite model dependence, fully developed inflationary scenarios predict testable signatures for current and future detectors like LIGO and LISA, offering a tangible link between cosmology and string theory.

Abstract

It is possible that superstrings, as well as other one-dimensional branes, could have been produced in the early universe and then expanded to cosmic size today. I discuss the conditions under which this will occur, and the signatures of these strings. Such cosmic superstrings could be the brightest objects visible in gravitational wave astronomy, and might be distinguishable from gauge theory cosmic strings by their network properties.

Figures (3)

• Figure 1: When two strings of the same type collide, they either reconnect, with probability $P$, or pass through each other, with probability $1-P$. For classical solitons the process is deterministic, and $P=1$ for the velocities relevant to the string network.
• Figure 2: Instabilities of macroscopic strings: a) Confinement by a domain wall. b) Breakage.
• Figure 3: Gravitational wave cusp signals, taken from Damour and Vilenkin Damour:2001bk. The horizontal axis is $\log_{10} \alpha$ where $\alpha = 50G\mu$. Thus the brane inflation range $10^{-12} \stackrel{<}{{_\sim}} G\mu \stackrel{<}{{_\sim}} 10^{-6}$ becomes $-10.3 < \log_{10} \alpha < -4.3$. The vertical axis is $\log_{10} h$ where $h$ is the gravitational strain in the LIGO frequency band. The upper and lower dashed horizontals are the sensitivities of LIGO I and Advanced LIGO at one event per year. The upper two curves are the cusp signal under optimistic and pessimistic network assumptions. The lowest solid curve is the signal from kinks, which form whenever strings reconnect. The dashed curve is the stochastic signal.