Hello Florian,

while going through the calculation of the C9 Wilson coefficient, I noticed that there are no photonic penguin
contributions in the subroutine CalculatePengV2d2L. I know that FlavorKit calculates b -> s gamma and from there
one can easily construct the photonic penguin contribution, but is it somehere done in the code?

Sincerely,
SoundSonic1

Hi,

CalculatePengVxxx includes only the contributions from massive gauge bosons. The effective gluon/photon couplings are calculated in CalculateGamma2Q, CalculateGluon2Q

Cheers,
Florian

Hi Florian,

shoudn't you include the photonic contributions for processes like b -> s l l ?
For example, the decay B -> K mu+ mu- would require the coefficients C7, C9 and C10
and from your routine one would miss the photon contribution to the vector operator
corresponding to C9.

Sincerely,
SoundSonic1

Hi,

no, massless gauge bosons behave differently and contribute only to 'monopole' operators (C7,C8) while massive ones to 'dipole' operators. This is analog to the discussion of lepton flavour violation processes which we have in 1408.0138.

Cheers,
Florian

Hi Florian,

it seems that there is some kind of misunderstanding in what you and I refer to as C7,..,C10 Wilson coefficients.
I was talking about the conventional basis for b physics which can be found
here: https://wcxf.github.io/assets/pdf/WET.flavio.pdf

The C7 coefficient corresponds to the magnetic dipole operator which is different than the one i was talking about.
The photon should contribute to the C7 and the C9. The 'monopole' operator you were refering to is actually the C9.

Sincerely,
SoundSonic1