PD Dr. Maximilian Stahlhofen

I will describe a state-of-the-art functional integration approach to integrate out heavy fields of beyond Standard Model (BSM) theories at the one loop level. The operators of the resulting effective field theory (EFT) encode the effects of the heavy loops in their Wilson coefficients. The method is based on the background-field formalism and the expansion by regions. As an illustrative example I will discuss the derivation of the low-energy EFT for a singlet extension of the Standard Model by integrating out the heavy BSM Higgs mass eigenstate. I will particularly focus on the mixing of the Higgs fields in the BSM model and show that as a consequence the proper EFT cannot be accommodated in the SMEFT framework.