Scaling from gauge and scalar radiation in Abelian Higgs string networks
Scaling from gauge and scalar radiation in Abelian Higgs string networks
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阿贝尔希格斯弦网络中规范辐射和标量辐射的缩放
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发表时间：
2017
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通讯作者：
M. Kunz
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作者：
M. Hindmarsh;J. Lizarraga;J. Urrestilla;David Daverio;M. Kunz
我们研究了阿贝尔希格斯模型中的宇宙弦网络，使用了在高达$4096^3$网格点的格子上进行的大规模数值模拟活动的数据。我们观察了网络在大尺度范围内的尺度或自相似性，并估计了平均弦在视界长度单位$dot{xi}$和平均弦平方速度$ar v^2$在连续体和大时间限制下的渐近值。尺度化的发生是因为弦在阿贝尔希格斯模型的标量场和规范场的经典辐射中损失了能量。我们用一个无量纲的辐射效率参数量化了能量损失，并表明它不随晶格间距或弦分离而显著变化。这意味着标度行为背后的辐射能量损失不是晶格伪像，并证明了将测量到的网络特性外推到宇宙扰动计算的大时间是合理的。我们还表明，核生长方法随着时间的推移增加缺陷核宽度以扩大模拟的动态范围，不会引入明显的系统误差。我们将$dot{xi}$和$ar v^2$与使用nambo - goto近似的模拟测量值进行比较，发现后者低估了平均字符串间隔约25%，而高估了$ar v^2$约10%。弦分离的尺度表明，在场论模拟中，弦环在哈勃时间内因大量辐射的发射而衰减，与忽略这种能量损失机制的Nambu-Goto情景形成对比。与南布-后藤情景相比，仅存活一个哈勃时间的弦环发出的引力辐射要少得多，因此它们的张力受到的引力波约束要弱得多。
We investigate cosmic string networks in the Abelian Higgs model using data from a campaign of large-scale numerical simulations on lattices of up to $4096^3$ grid points. We observe scaling or self-similarity of the networks over a wide range of scales, and estimate the asymptotic values of the mean string separation in horizon length units $dot{xi}$ and of the mean square string velocity $ar v^2$ in the continuum and large time limits. The scaling occurs because the strings lose energy into classical radiation of the scalar and gauge fields of the Abelian Higgs model. We quantify the energy loss with a dimensionless radiative efficiency parameter, and show that it does not vary significantly with lattice spacing or string separation. This implies that the radiative energy loss underlying the scaling behaviour is not a lattice artefact, and justifies the extrapolation of measured network properties to large times for computations of cosmological perturbations. We also show that the core growth method, which increases the defect core width with time to extend the dynamic range of simulations, does not introduce significant systematic error. We compare $dot{xi}$ and $ar v^2$ to values measured in simulations using the Nambu-Goto approximation, finding that the latter underestimate the mean string separation by about 25%, and overestimate $ar v^2$ by about 10%. The scaling of the string separation implies that string loops decay by the emission of massive radiation within a Hubble time in field theory simulations, in contrast to the Nambu-Goto scenario which neglects this energy loss mechanism. String loops surviving for only one Hubble time emit much less gravitational radiation than in the Nambu-Goto scenario, and are consequently subject to much weaker gravitational wave constraints on their tension.