Effective field theories for new heavy particles --renormalization and phenomenological applications

• Applicant: Professor Dr. Stefan Dittmaier
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 550270721

The aim of the project is to provide effective Lagrangians for phenomenologically interesting heavy-mass limits of SM extensions with non-standard Higgs sectors, such as a singlet-Higgs extension, the Two-Higgs Doublet Model, and the Babu Model, the latter featuring lepton-number-violating couplings. Building on the great progress made in recent years on so-called functional matching methods to derive Effective Field Theories (EFTs) directly from the path integral, we will construct the corresponding EFT Lagrangians up to order 1/Lambda^2, where Lambda is the generic new-physics mass scale. In detail, we make use of and further extend a functional method that we have presented in a publication in 2021, which has ist roots in earlier work from 1995/96. The method employs the background-field method for quantization, the method of regions for the separation of light and heavy field modes, and non-linear Higgs representations to be most flexible wrt. The emerging type of (weakly or strongly coupled) EFT. The project goes beyond existing related work in various respects. Firstly, we consistently take into account the full renormalization of the underlying UV-complete theory (a subject that is often neglected) and will compare next-to-leading-order predictions obtained in the full theory and in the EFT for physically interesting observables. Secondly, preliminary results from a simplified model already showthat the emerging EFT goes beyond the frequently used framework of "Standard Model EFT (SMEFT)" in phenomenologically interesting heavy-mass limits; the emerging EFT is rather of a type known as "Higgs EFT (HEFT)", which relies on non-linearly realized Higgs fields and is not very often considered in the context of EFT construction via functional matching.

• DFG Programme: Research Grants