New answers tagged functional-derivatives
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The variational derivative of the metric with respect to inverse metric
The correct expression is (1). The key point is that the derivative $\partial_\mu$ acts on the entire expression within the functional derivative, not just the delta function.
To see this, we start ...
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2
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Functional derivative of gauge fixing condition - Peskin QFT page 295
Hints:
Functional/variational differentiation
$$\frac{\delta\alpha(x)}{\delta\alpha(y)}=\delta^4(x\!-\!y)$$
here acts on different/independent spacetime points $x$ and $y$; not the same spacetime ...
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