MadGraph5_aMC@NLO

Chirality flip due to vev insertion

Asked by Taegyu Lee

Hi,

I am curious about how madgraph deals with the chiralities for fermions.
For example, if you are interested in the interaction between massive fermion and Higgs,
Higgs should couple to, for example, b{R} and b~{R}. I was expecting that h > b{R} b~{L} should be suppressed by order of m_b/vev because of the chirality flip due to vev insertion. However, I find that the result for h > b{R} b~{L} is much more suppressed than I thought compared to h > b{R} b~{R}.

So, I am curious whether madgraph automatically calculates the chirality flipped scenarios using vev insertion or not.

Thank you very much!

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

We use helicity amplitude to compute both contribution:
See: https://inspirehep.net/literature/336604

For the rest my advise would be to do such computation by hand (it is an easy one) to understand why the suppression is so large.

Cheers,

Olivier

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Taegyu Lee (taegyulee) said : 		#2

Hi,

Thank you very much for the quick answer!

I will go through the file you sent.

Best,
Taegyu