Dear Florian

Since SPheno does not calculate Z decay channels for instance to neutralino or chargino. How can I be sure that MG5 calculates them correctly? Should it be close to MSSM since SPheno doesn't give anything should x-section be MSSM like or should it be zero from Z. If so how can I make SPheno write Z decay channels to susy particles or is there a way to make MG5 to calculate it as MSSM like (if it's suppose to be MSSM like of course)

It also doesn't show the Z decays to leptons in SPhenoLowEnergy block (as written in 1104.1573) so maybe im missing a flag for Z hopefully?

Thanks
Best regards

Hi Jack,

you can force SPheno to calculate the decays into Z-bosons by giving the list of all particles explicitly as for instance done in the model BLRinvSeesaw However, you shouldn't be surprised if the value which you get for the width doesn't agree with the SM one: SPheno does a pure tree-level calculation, while in the SM many higher order corrections are included, of course. Thus, it makes no sense to put constraints on the width as calculated by SPheno to exclude new physics scenarios where decays into neutralinos are present. You would also exclude points with decays only in SM states because the difference tree-level to the full calculation is much larger than the experimental uncertainty in the Z-width.
What you can do is to take the ratio of the widths as calculated by SPheno with and without decays into BSM states and put a limit there.

Cheers,
Florian