Gauge invariant incorporation of particle widths?

1. Jun 19, 2006

EL

Introducing particle width via the Breit-Wigner propagator can break gauge invariance.
Anyone know of some "nice" way to incorporate widths while still retaining gauge invariance?

2. Jun 19, 2006

EL

3. Jun 20, 2006

Meir Achuz

You could try replacing m^2 in denominators by (m-i\gamma/2)^2.
If that breaks GI, just stay in that particular gauge.

4. Jun 21, 2006

EL

I'm not really able to see how that method gives hope to retain gauge invariance if the ordinary Breit-Wigner fails? I mean, all it does just to add one more term, quadratic in "gamma", in the denominators?

(And for two simple cases I've checked, Compton scattering and electron-positron annihilation, it doesn't help to restore GI.)

5. Jun 21, 2006

Meir Achuz

If an approximation breaks GI. You can do everything in that gauge.
You don't need GI to complete an approximate calclation.

6. Jun 21, 2006

EL

I would like to have a gauge invariant amplitude since I suspect strong cancelations are important in the certain process I'm interested in.

If I do as you suggest and just stick to a certain gauge, which one is the "correct" to be in when I insert the width in the propagators?