This is probably a dumb question, but I have a book that claims that if you have a function of the momentum squared, f(p(adsbygoogle = window.adsbygoogle || []).push({}); ^{2}), that:

[tex]\frac{d}{dp^2}f=\frac{1}{2d}\frac{\partial }{\partial p_\mu}

\frac{\partial }{\partial p^\mu}f[/tex]

where the d in the denominator is the number of spacetime dimensions, so for 4-space the numerical factor would be 1/8.

But this seems to only be true if your function is the identity [itex]f(p^2)=p^2 [/itex], and doesn't hold for all functions f(p^2).

So is the book wrong?

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# Derivative of a function of a lorentz scalar

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