Abstract
One of the assumptions of simplified models is that there are a few new particles and interactions accessible at the LHC and all other new particles are heavy and decoupled. The effective field theory (EFT) method provides a consistent method to test this assumption. Simplified models can be augmented with higher order operators involving the new particles accessible at the LHC. Any UV completion of the simplified model will be able to match onto these beyond the Standard Model EFTs (BSM-EFT). In this paper we study the simplest simplified model: the Standard Model extended by a real gauge singlet scalar. In addition to the usual renormalizable interactions, we include dimension-5 interactions of the singlet scalar with Standard Model particles. As we will show, even when the cutoff scale is 3 TeV, these new effective interactions can drastically change the interpretation of Higgs precision measurements and scalar searches. In addition, we discuss how power counting in a BSM-EFT depends strongly on the processes and parameter space under consideration. Finally, we propose a $\chi^2$ method to consistently combine the limits from new particle searches with measurements of the Standard Model. Unlike imposing a hard cut off on heavy resonance rates, our method allows fluctuations in individual channels that are consistent with global fits.
Highlights
The Large Hadron Collider (LHC) has had two very successful runs
We study the beyond the Standard Model (BSM)-effective field theory (EFT) of the simplest possible extension of the SM, the addition of a real scalar singlet S [21,22,23]
II, we develop the beyond the Standard Model EFTs (BSM-EFT) for the real scalar singlet
Summary
The Large Hadron Collider (LHC) has had two very successful runs. While no new physics beyond the Standard Model (BSM) has been discovered, we may yet expect it to show up in currently unanalyzed data or in future runs at the LHC. The new singlet only enters the scalar potential, and its interactions with fermions and gauge bosons are inherited by its mixing with the SM Higgs boson. While these effects can be important, we are interested in the question of how the EFT including new particles can change the phenomenology of the simplified models. In order to focus on the effects of new physics on the scalar singlet properties, we will consider only dimension-5 EFT operators. At dimension-5, the only SMEFT operators are those that contribute to Majorana neutrino masses [5,6,42], which are not relevant for LHC analyses These will be neglected and the BSM-EFT will only consist of operators including the new singlet scalar.
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