It is generally accepted that consistent coupling to quantum gravity implies that any low energy free parameter is in reality the vacuum expectation value of some local quantum field. In this note we present a modest attempt to prove this general claim using as key example the θ parameter of QCD and the Peccei‐Quinn axion solution of the strong CP problem. The gravitational emergence of the local axion field associated with the superselection θ parameter is worked out using as basic ingredients the quantum representation of classical geometries in terms of coherent states and the interpretation of the θ QCD superselection rule in quantum information terms as the lack of a quantum reference frame for topological charge. The formal connection with the model independent axion in string theory is briefly discussed.

中文翻译：

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重力，超选规则和轴

公认的是，与量子引力的一致耦合意味着任何低能量自由参数实际上都是某个局部量子场的真空期望值。在本说明中，我们将以QCD的θ参数和强CP问题的Peccei-Quinn轴力解作为关键示例，以适度的尝试来证明这一一般性主张。与超选择θ参数相关的局部轴突场的引力出现是使用经典几何的相干态的量子表示和量子信息中的θQCD超选择规则的解释作为基本成分来计算的，以此作为基本成分。拓扑电荷的量子参考框架。简要讨论了弦理论中与模型独立轴之间的形式联系。