Cosmic topological defects from holography

This work investigates cosmic topological defects in gauge theories, focusing on models with an SU(N) gauge group coupled with a single flavor, explored through a holographic framework. At low energies, the effective theory is described by an axion-like particle resulting from the spontaneous breaking of the axial U(1)A flavor symmetry. As the Universe cools below a critical temperature, the chiral symmetry is broken, and non-trivial vacuum configurations form, resulting in the creation of cosmic strings and domain walls. We provide a UV description of these defects in a particular holographic theory, the Witten-Sakai-Sugimoto model, as probe D6-branes. We show the presence of a first-order phase transition separating string loop from domain wall solutions. String loops charged under the baryon symmetry and with angular momentum — vortons — can be understood as excitations of a topological phase of matter given by a Chern-Simons theory living on the D6-brane world volume. Finally, we provide an effective description of string loops and vortons in terms of degrees of freedom living on the flavor brane, i.e. mesonic modes.