# Dirac delta to the fourth

1. Jan 26, 2013

### zn5252

hello,
Please attached snapshot. Does the integral 7.9 equal to 0.5 $\int$hμσ dzμ/dτ dzσ/dτdτ ?
I'm confused as to the fourth power of Dirac's Delta. Then where does the derivative on x go ?
For more on this, see MTW pg180
thanks

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2. Jan 26, 2013

### Bill_K

It's not a 4th power, it means a four-dimensional delta function. I.e. in Minkowski coordinates,

δ4(x - x') = δ(x - x')δ(y - y')δ(z - z')δ(t - t')

Ofttimes you would integrate this over all four dimensions. In this case there is only one integration, leaving three δ's, so it means that Tμν(x) is concentrated on the particle's worldline.