SU（N）规范理论中的闭k弦：2+1维
Closed k-strings in SU(N) gauge theories : 2+1 dimensions
摘要：
在（2+1）维SU（N）规范理论中，计算了N= 4，5，6，8和k= 2，3，4时闭k弦的基态能量.从基态能量对弦长度的依赖性，我们推断这样的k弦是由一个有效的弦论描述的，它与基本弦属于同一个玻色子普适类（南武-后藤）。当我们比较连续k弦张力和相应的基本弦张力时，我们发现它们的比值接近于某些理论方法所支持的卡西米尔标度值，但通常比卡西米尔标度值高出1- 2%。以一种与模型无关的方式拟合N-依赖性有利于1/N的扩展（如在卡西米尔标度中），而不是朴素的颜色计数所建议的1/N^2。我们还观察到k弦态的低位谱落入属于SU（N）的特定不可约表示的扇区，这表明弦束缚的动力学知道完整的规范群，而不仅仅是它的中心。
英文摘要：
We calculate the ground state energies of closed k-strings in (2+1)-dimensional SU(N) gauge theories, for N=4,5,6,8 and k=2,3,4. From the dependence of the ground state energy on the string length, we infer that such k-strings are described by an effective string theory that is in the same bosonic universality class (Nambu-Goto) as the fundamental string. When we compare the continuum k-string tensions to the corresponding fundamental string tensions, we find that the ratios are close to, but typically 1-2 percent above, the Casimir scaling values favoured by some theoretical approaches. Fitting the N-dependence in a model-independent way favours an expansion in 1/N (as in Casimir scaling) rather than the 1/N^2 that is suggested by naive colour counting. We also observe that the low-lying spectrum of k-string states falls into sectors that belong to particular irreducible representations of SU(N), demonstrating that the dynamics of string binding knows about the full gauge group and not just about its centre.
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