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

[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?

 

[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

 

[spaghetti3451]

Could you be more specific?

 

[Deneen2000]

]

 

[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...

 

[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.