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Gauge invariant incorporation of particle widths?

  1. Jun 19, 2006 #1

    EL

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    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?
     
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  3. Jun 19, 2006 #2

    EL

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  4. Jun 20, 2006 #3

    Meir Achuz

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    You could try replacing m^2 in denominators by (m-i\gamma/2)^2.
    If that breaks GI, just stay in that particular gauge.
     
  5. Jun 21, 2006 #4

    EL

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    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.)
     
  6. Jun 21, 2006 #5

    Meir Achuz

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    If an approximation breaks GI. You can do everything in that gauge.
    You don't need GI to complete an approximate calclation.
     
  7. Jun 21, 2006 #6

    EL

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    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?
     
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