• simulation numerical techniques cosmic strings sim

The thesis treats theoretically and through numerical simulations some features of cosmic strings. These are topological defects which may form during phase transition in cosmological epochs. These structures can be compatible with experimental observations such us CMB. This characteristic differentiate them with respect to monopoles and domain walls.
Neglecting interactions curvature effects an appropriate description of cosmic strings’ dynamics is furnished by Nambu action. We deal with a (1, 3)-dimensional space-time and this allows us to treat these objects as relativistic strings.
We derive equations describing motion of cosmic strings in the Minkowski and FRW space-time and we reason on the possibility that a scaling solution manifests. The search for this particular in- stance is motivated by some features of the action used to describe cosmic strings. Nambu action indeed hints the possibility for this system to lodge a single scale.
Some typical feature of the non Abelian case are presented. Par- ticularly we point out the possibility of forming complex structures which may not occur in the Abelian scenario. This property at least theoretically may void some results derived assuming Abelianity.
In literature some pathological aspects of scaling solution has been highlighted. Two articles try to furnish numerical predictions on non Abelian cosmic strings networks. Their results are not in complete agreement and this motivates our interest in a new detailed discussion regarding the topic. The goal of our speculations is to provide a modeling for a network of non Abelian cosmic strings.
We critically examined the results proposed in one of this articles trying to perceive what may cause effects which could affect numerical simulation. We repeated the simulation, measuring some new observables in order to clarify statistical properties of the network.
We also examined a different which poses emphasis on the dynamics of the strings. In a non Abelian theory the interconnection of two strings can produce configurations containing vertices where three strings are connected. This problem is treated with a theoretical approach. We attempted to define the most natural action to describe these objects and then we derived the equations of motion describing the evolution of these structures.