I know the generalized formula for Feynman parameters, my problem is in simplifying.(adsbygoogle = window.adsbygoogle || []).push({});

What I mean is something like this:

Take the simplest 3 parameter equation

[itex] \frac{1}{ABC} = 2 \int_0^1 dx \int_0^1 dy \int_0^1 dz \frac{ \delta \left( 1-x-y-z \right)}{(xA+yB+zC)^3} [/itex]

And you can take this and put move to two integrals by integrating over z, I understand that we use the delta function to get (xA+yB+(1-x-y)C)^{3}in the denominator of the new integrand...however, I don't understand why we now have:

[itex] 2 \int_0^1 dx \int_0^{1-x} dy[/itex]

I've done it out by hand to check it, so I know this is what we need...but why do we substitute in 1-x for the limit of integration?

This is probably a dumb question, but I need to know so I can generalize to four parameters.

Thanks for any and all help!

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# Reallllly dumb question about Feynman Parameters (and simplifying them)

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