automatic detection of zero couplings

Registered by Olivier Mattelaer

in presence of zero couplings we should avoid
1) avoid computation of wavefunctions/amplitudes
2) avoid to run the channel of integration

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Complete
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Needs approval
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Obsolete
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Completed by
Olivier Mattelaer

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Hello Olivier,

Partly, this would be easy enough, but is it really worth it? What are the examples you are thinking about? I would guess you are thinking in particular about using full models with restrictive parameter cards, where e.g. CKM matrix elements are set to 0?

To the extent that ALOHA amplitudes are always multiplied by the coupling, it's easy enough to identify, for all amplitudes, which couplings would render this amplitude zero. We can then simply check, both for the amplitude used for the present channel, and for the diagram (or perhaps, as you suggest, wavefunction) calculation. Note however, that in your combined ALOHA couplings, we will need to check multiple couplings.

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This is not exactly the same but the 2.9.0 branch will automatically remove any amplitude/wavefunction leading to 0 matrix element (per helicity). So the only case which is not cover in the above idea is in presence of the combined ALOHA couplings since in that case the associated matrix-element will not be zero.

(?)

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