New physics in the Higgs sector - an effective theory approach
Prof. Gerhard Buchalla (LMU)
Measurements of Higgs couplings are so far compatible with the standard model, but substantial deviations of order 10% or more are still allowed. Anomalous Higgs couplings might therefore be the largest new-physics effects in the electroweak sector, potentially dominating over those in the well-constrained gauge interactions. Such a scenario is expected in models of dynamical electroweak symmetry breaking. Its test will be a central goal of the LHC program and is well matched to the projected sensitivity of few percent with 300 fb-1 of integrated luminosity to be collected in run 2 and 3.
The natural framework to describe sizable new physics in the Higgs couplings, formulated as a consistent effective field theory (EFT), is provided by the electroweak chiral Langrangian. Its systematics will be discussed, in particular the power counting by chiral dimensions, equivalent to a loop expansion. The chiral Lagrangian reduces, at leading order, to a parametrization of Higgs couplings that is widely used in experimental studies (kappa-formalism). The latter thus receives a proper quantum field theory justification. The results of a fit of Higgs couplings to current data within this framework will also be presented, emphasizing the EFT interpretation.