### Conveners

#### From Cosmic Strings to Superstrings: Block 1

- Carlos Martins (CAUP)
- Ivan Rybak (Instituto de Astrofísica e Ciências do Espaço (IA), Porto)

### Description

Cosmic strings arise naturally in many proposed theories of new physics beyond the standard model, including superstring inspired inflation models. In the latter case, fundamental superstrings may have stretched to macroscopic scales, known as cosmic superstrings. If observed, these objects provide a unique window into the early universe. Recent observational progress highlights how some of these scenarios could be constrained, but they also show a bottleneck in the lack of accurate high-resolution network simulations that can be used as templates for robust statistical analysis. Additionally, most numerical simulations and analytic modeling so far are for the simplest cosmic strings, while realistic ones might have nontrivial internal structure, implying that current constraints are unreliable for these scenarios. This session will discuss recent progress in numerical simulations and analytic modeling, with a view to obtaining a more reliable assessment of the cosmological roles of these networks.

The canonical velocity-dependent one-scale (VOS) model for cosmic string evolution contains a number of free parameters which cannot be obtained ab initio. Therefore it must be calibrated using high resolution numerical simulations. We exploit our state of the art graphically accelerated implementation of the evolution of local Abelian-Higgs string networks to provide a...

The evolution of cosmic strings, in particular cosmic string loops, has been an open question for a number of years. The dynamics observed by field theory lattice simulations and by the Nambu-goto approximation do not agree, giving big differences in the lifetimes of loops, which for example affects their gravitational wave production.

In this talk we will discuss the results obtained from...

There has been significant progress in recent years on modelling the evolution of cosmic string and cosmic superstring networks. As we are targeting gravitational wave signals from strings, attention is shifting to the closed string (loop) component of those networks. The predicted signal depends on a number of parameters, some of which are assumed/argued to be of order unity. I will focus on...

Cosmic strings may have formed in the early universe due to the Kibble mechanism. While string networks are usually modeled as being of Nambu-Goto type, this description is understood to be a convenient approximation, which neglects the typically expected presence of additional degrees of freedom on the string worldsheet. Previous simulations of cosmic strings in expanding universes have...

We study the axion strings with the electroweak gauge flux in the DFSZ axion model and show that these strings, called the electroweak axion strings, can exhibit superconductivity without fermionic zero modes. We construct three types of electroweak axion string solutions. Among them, the string with W-flux can be lightest in some parameter space, which leads to a stable superconducting cosmic...

In the QCD axion dark matter scenario with post-inflationary Peccei-Quinn symmetry breaking, the number density of axions, and hence the dark matter density, depends on the length of string per unit volume at cosmic time $t$, by convention written $\zeta/t^2$. The expectation has been that the dimensionless parameter $\zeta$ tends to a constant $\zeta_0$, a feature of a string network known as...

We present results from adaptive mesh refinement (AMR) simulations of global cosmic strings. Using the public code, GRChombo, we perform a quantitative investigation of the dynamics of single sinusoidally displaced string configurations. We study a wide range of string energy densities $\mu \propto \ln{\lambda}$, defined by the string width parameter $\lambda$ over two orders of magnitude. We...