The probability density of the dirac spinor is known to be ∑(Ψ)(adsbygoogle = window.adsbygoogle || []).push({}); ^{2}and I know how it is derived. However, I'm just wondering why it should be positive definite. Since the lower two components represent antiparticles, so shouldn't the probability density contribution of those two components be negative? Or actually what does that probability density represent? Thanks!

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# A Probability density of dirac spinors

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