For the electric polarizability of a bound system in relativistic quantum theory, there are two definitions that have appeared in the literature. They differ depending on whether or not the vacuum background is included in the system. A recent confusion in this connection is clarified.
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We can start with a negative energy bound state. If we do so, however, we will meet unnecessary, nonessential complications in the contexts of QFT.
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© 1999 American Association of Physics Teachers.
1999
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