无质量粒子理论的超真空与超选择结构
On Infravacua and the Superselection Structure of Theories with Massless Particles
摘要：
在无质量粒子的量子场论中，与真空相比，携带非平凡超选择电荷的态可能具有非常差的局域化性质。在这种情况下，用合适的“亚真空”状态代替真空可以改善电荷的局域性，使得超选择扇区的多普利歇-哈格-罗伯茨（DHR）理论适用。作为这种现象的一个明确的例子，我们考虑了自由无质量标量场的某一类扇区。这些扇区带有电荷，相应的亚真空背景可以解释为红外辐射云。出于这种情况下，我们提出了一个模型独立的定义亚真空表示，并推导出它们的一些性质。我们特别分析了它们作为DHR理论的参考表示的作用，并研究了在何种程度上不存在平移不变向量会影响DHR分析的结果。特别强调的是放在函的理论方面和描述的协方差和频谱特性的收费部门在所谓的电荷传输cocycles。
英文摘要：
In quantum field theories with massless particles, states carrying a nontrivial superselection charge may have very poor localisation properties when compared to the vacuum. In this case, replacing the vacuum with a suitable ``infravacuum'' state can improve the localisability of the charges in such a way that the Doplicher-Haag-Roberts (DHR) theory of superselection sectors is applicable. As an explicit example for this phenomenon, we consider a certain class of sectors of the free massless scalar field. These sectors carry a charge of electric type, and the corresponding infravacuum background may be interpreted as a cloud of infrared radiation. Motivated by this situation, we propose a model-independent definition of infravacuum representations and derive some of their properties. We analyse in particular their role as reference representations for DHR theory and investigate to what an extent the absence of a translation invariant vector affects the results of the DHR analysis. Special emphasis is put on the functorial aspects of the theory and on the description of the covariance and the spectral properties of charged sectors in terms of so-called charge transporting cocycles.
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