A Fermionic Top Partner: Naturalness and the LHC

TL;DR

This paper explores a simple fermionic top partner model addressing naturalness in the Higgs sector, analyzing its phenomenology, current experimental bounds, and potential observable deviations in Higgs decay rates.

Contribution

It provides a detailed phenomenological study of a fermionic top partner model, including bounds from experiments and predictions for Higgs decay deviations.

Findings

Lower bounds on top partner mass: ~500 GeV from electroweak data, ~450 GeV from LHC.

The model allows a 125 GeV Higgs with about 20% fine-tuning.

Potential observable deviations in Higgs decay rates to gauge bosons.

Abstract

Naturalness demands that the quadratic divergence of the one-loop top contribution to the Higgs mass be cancelled at a scale below 1 TeV. This can be achieved by introducing a fermionic (spin-1/2) top partner, as in, for example, Little Higgs models. In this paper, we study the phenomenology of a simple model realizing this mechanism. We present the current bounds on the model from precision electroweak fits, flavor physics, and direct searches at the LHC. The lower bound on the top partner mass from precision electroweak data is approximately 500 GeV, while the LHC bound with 5/fb of data at sqrt(s)=7 TeV is about 450 GeV. Given these bounds, the model can incorporate a 125 GeV Higgs with minimal fine-tuning of about 20%. We conclude that natural electroweak symmetry breaking with a fermionic top partner remains a viable possibility. We also compute the Higgs decay rates into gauge bosons, and find that significant, potentially observable deviations from the Standard Model predictions may occur.