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Abstract: We study the evolution of non-periodic cosmic string loops containingY-junctions, such as may form during the evolution of a network of p,q cosmicsuperstrings. We set up and solve the Nambu-Goto equations of motion for a loopwith junctions, focusing attention on a specific static and planar initial loopconfiguration. After a given time, the junctions collide and the Nambu-Gotodescription breaks down. We also study the same loop configuration in aU1xU1 field theory model that allows composite vortices with correspondingY-junctions. We show that the field theory and Nambu-Goto evolution areremarkably similar until the collision time. However, in the field theoryevolution a new phenomenon occurs: the composite vortices can unzip, producingin the process new Y-junctions, whose separation may grow significantly,destabilizing the configuration. In particular, an initial loop with twoY-junctions may evolve to a configuration with six Y-junctions all distantfrom each other. Setting up this new configuration as an initial condition forNambu Goto strings, we solve for its evolution and establish conditions underwhich it is stable to the decay mode seen in the field theory case. Remarkably,the condition closely matches that seen in the field theory simulations, and isexpressed in terms of simple parameters of the Nambu-Goto system. This impliesthat there is an easy way to understand the instability in terms of whichregion of parameter space leads to stable or unstable unzippings.

Autor: Neil Bevis, Edmund J. Copeland, Pierre-Yves Martin, Gustavo Niz, Alkistis Pourtsidou, Paul M. Saffin, D. A. Steer

Fuente: https://arxiv.org/

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