# A Relative sign in diagrams for $Z$-boson exchange for $WW$ scattering

1. Mar 26, 2017

### spaghetti3451

Consider the scattering process $W^{+}W^{-} \to W^{+}W^{-}$. This process is mediated in the Standard Model by

1. a four-$W$ scattering,
2. $Z$-boson exchange,
3. Higgs exchange.

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Let us consider the diagrams for $Z$-boson exchange:

Why is there a relative minus sign between the matrix elements for the two diagrams?

2. Mar 26, 2017

### Deneen2000

Newbie here...have you considered that the relative minus sign btwn two terms is dictated by the Fermi-Dirac stats? something about a possible closed loop - which carries the extra minus sign.

I hope this helps.

Deneen

3. Mar 26, 2017

### spaghetti3451

Could you be more specific?

4. Mar 26, 2017

### Deneen2000

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5. Mar 27, 2017

### ChrisVer

how can you use Fermi-Dirac statistics for W/Z bosons?
Also I think that that minus sign mentioned in your reference appears between t- and u- channels...

Last edited: Mar 27, 2017
6. Mar 27, 2017

### CAF123

@spaghetti3451 Could you explain why you think there should be a relative minus in the first place for this process? There is no u channel process here in the case of a Z mediator.