what's effective charge?
To give a quick answer (because I have to leave soon), an effective charge arises when you have a charged particle surrounded by a polarizeable medium, for example an electron in a metal is surrounded by positive charges. What happens is that the electron attracts the positive charge centers to it, so there's this quasi-particle with an effective charge where the positive charges are screening the electron's "bare charge", so the electron appears to have a lower charge than we would measure if we just isolated an electron and measured the charge.
A similar effect can happen if you throw in QFT in the vacuum, but I don't know a great deal about that and will let someone else handle it.
thank you very much!!!
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