Cosmic F- and D-strings

TL;DR

This work analyzes the stability of cosmic strings within string-theory constructions, showing that metastable macroscopic F- and D-strings can persist in warped compactifications and that (p,q) bound states provide a rich observational arena. By deriving stability criteria against breakage and axion-domain-wall confinement and applying them to the KKLT/KKLMMT inflation framework, it identifies scenarios with no strings, D-string–only strings, or $(p,q)$ string networks with p-bounds set by throat fluxes. It then extends the discussion to large-dimension models and outlines the distinctive observational signatures, especially in gravitational waves, CMB constraints, and string-network dynamics, highlighting a potentially deep observational window into string theory. The findings underscore that the existence and properties of cosmic strings are highly model-dependent but could furnish a direct probe of fundamental string physics if metastable strings survive after inflation.

Abstract

Macroscopic fundamental and Dirichlet strings have several potential instabilities: breakage, tachyon decays, and confinement by axion domain walls. We investigate the conditions under which metastable strings can exist, and we find that such strings are present in many models. There are various possibilities, the most notable being a network of (p,q) strings. Cosmic strings give a potentially large window into string physics.