| 单词 | theta vacuum |
| 释义 | theta vacuum(θ vacuum) The vacuum state for non-Albelian gauge fields (in the absence of fermion fields and Higgs fields). In the theta vacuum there is an infinite number of degenerate states with tunnelling (see tunnel effect) between these states. This means that the theta vacuum is analogous to a Bloch function (see Bloch's theorem) in a crystal. This can be derived either as a general result or using instanton techniques. When a massless fermion field is present the tunnelling between states is completely suppressed. When there are fermion fields with a small mass tunnelling is much smaller than for pure gauge fields, but is not completely suppressed. The theta vacuum is the starting point of understanding the vacuum state in strongly interacting gauge theories, such as quantum chromodynamics |
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