On-shell methods have proven to be very useful for calculations in effective field theories. In this seminar, I discuss how they allow to simplify the calculation of finite contributions from heavy particles to Wilson coefficients. I apply this technique to the calculation of the Wilson coefficients of operators contributing to g − 2 and Higgs decays to photons, and show how the finite contributions can be obtained from the product of tree-level amplitudes. In certain cases, due to a parity symmetry of these amplitudes, the total contribution to the Wilson coefficients adds up to zero, as previously found in the literature. The method that I present allows to search for new natural zeros, as well as to obtain non-zero contributions in a straightforward way.

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