MadGraph5_aMC@NLO

automatic computation of the decay width

Asked by Magdy Louka

Hello all
i am generating events for BSM theory using madgraph at p-p collisions and i set the decay width of the new particles to auto, while the run i get this notification:-

"Please note that the automatic computation of the width is only valid in narrow-width approximation and at tree-level".

have i to care about this ?

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Yes you do

We do not check if those hypothesis are valid.
So this is your responsability to check those:
1) you are indeed in narrrow-width approximation
2) that you do not have loop-induced decay for such particle (or at least that they are negligeable)
3) that you do not need NLO accuracy for such width computations

In principle we could have not include that message since those are clearly stated in the associated paper (1402.1178 ) but It is always good to remind the hyppothesis used when creating a code (especially the loop-induced one)

Cheers,

Olivier

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