Axiverse Strings
  If the QCD axion solves the strong CP problem then light axion-like-particles
(ALPs) are expected to be ubiquitous in string theory - the string axiverse.
Such ALPs can be the QCD axion and constitute dark matter (DM) or radiation,
quintessence, and lead to new forces. String ALPs are also expected to give
rise to a multiplicity of cosmologically important global axion strings. We
study the properties of these axiverse cosmic strings including the vital
effects of moduli stabilization, and find that the string cores provide
`portals' to different decompactifications - to be precise, the cores explore
the large K\"ahler or complex structure boundary of moduli space. As usual for
global strings the tension $T_1\sim \Lambda^2 \log(L\Lambda)$ with inter-string
separation, $L$, while $\Lambda$ can be small $\ll M_{\rm pl}$. At long
distances from the string there are potential new signatures involving
variations in Standard Model (SM) parameters (Yukawa couplings, gauge
couplings, masses) and equivalence principle violations.
