# Problem: Prove invariance of momentum factor

1. Apr 13, 2010

### popffabrik1

Hi,

In the derivation of scattering amplitudes (e.g. page 94 in http://kcl.ac.uk/content/1/c6/06/20/94/LecturesSM2010.pdf [Broken]) does anyone have a clue as to how to prove that the momentum uncertainty element

(\delta p)^3/E

is Lorentz invariant? I know how to do it for the measure d^3p/E, but I am not sure how to proceed for the given (non-infinitesimal) element.

Thank,

P

Last edited by a moderator: May 4, 2017
2. Apr 14, 2010

### ansgar

I would say that it is proven in the same was as for the measure.

3. Apr 15, 2010

### popffabrik1

For the measure, you prove it by noting that
\int d^4p \delta(p^2)
is a lorentz invariant and by the properties of the dirac delta function this reduces to the given measure over three momentum. I don't see how there would be an analog in the case of 'errors'