Evolution and stability of cosmic string loops with Y-junctions
Evolution and stability of cosmic string loops with Y-junctions
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具有 Y 形结的宇宙弦环的演化和稳定性
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
D. Steer
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作者：
Neil Bevis;E. Copeland;Pierre;G. Niz;A. Pourtsidou;P. Saffin;D. Steer
我们研究了非周期性宇宙弦环的演化，其中包含Y-结，例如可能在（p，q）宇宙超弦网络的演化过程中形成。我们建立并解决了Nambu-Goto方程的运动与路口的循环，专注于一个特定的静态和平面的初始循环配置。在给定的时间之后，交叉点发生碰撞，Nambu-Goto描述失效。我们还研究了U（1）× U（1）场论模型中相同的环结构，该模型允许具有相应Y结的复合涡。我们表明，场理论和南部后藤演化是非常相似的，直到碰撞时间。然而，在场论的发展中出现了一个新的现象：复合涡可以解压缩，在这个过程中产生新的Y形结，其分离可能会显着增长，使构型不稳定。特别地，具有两个Y接头的初始环可以演变为具有六个Y接头（彼此远离）的配置。设置这个新的配置为Nambu后藤字符串的初始条件，我们解决了它的演变，并建立条件下，它是稳定的衰减模式中看到的场论的情况下。值得注意的是，该条件与场论模拟中所见的条件非常匹配，并且以Nambu-Goto系统的简单参数表示。这意味着有一种简单的方法来理解不稳定性，即参数空间的哪个区域导致稳定或不稳定的解压缩。
We study the evolution of non-periodic cosmic string loops containing Y-junctions, such as may form during the evolution of a network of (p,q) cosmic superstrings. We set up and solve the Nambu-Goto equations of motion for a loop with junctions, focusing attention on a specific static and planar initial loop configuration. After a given time, the junctions collide and the Nambu-Goto description breaks down. We also study the same loop configuration in a U(1)xU(1) field theory model that allows composite vortices with corresponding Y-junctions. We show that the field theory and Nambu-Goto evolution are remarkably similar until the collision time. However, in the field theory evolution a new phenomenon occurs: the composite vortices can unzip, producing in the process new Y-junctions, whose separation may grow significantly, destabilizing the configuration. In particular, an initial loop with two Y-junctions may evolve to a configuration with six Y-junctions (all distant from each other). Setting up this new configuration as an initial condition for Nambu Goto strings, we solve for its evolution and establish conditions under which 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 is expressed in terms of simple parameters of the Nambu-Goto system. This implies that there is an easy way to understand the instability in terms of which region of parameter space leads to stable or unstable unzippings.