The Higgs boson and the top quark

Figure 1: Loop corrections to the Higgs mass are dominated by top quark loops.

The discovery of a Higgs boson at a mass of about 125 GeV in 2012 in proton-proton collision data provided by the Large Hadron Collider (LHC) answers the question of how elementary particles acquire mass, via the Higgs mechanism. The top quark is the heaviest elementary particle discovered so far, and hence a very special quark. It has a mass of about 173 GeV, which almost corresponds to the mass of a gold atom. In a future theory of particle physics, based on our current best theoretical model (standard model, SM), the mass of the Higgs boson gets affected by loop corrections, which are dominated by the top quark.

Figure 1 shows the loop corrections to the Higgs mass due to the top quark. Since the momentum of the top quark is not limited, the corrections to the Higgs mass are huge:

\Delta m^2(h) \propto \Lambda^2_{\mathrm{Cutoff}}.

In fact they correct the Higgs mass to a mass of about 1019 GeV (aka Planck scale), in strong disagreement to the experimental data. This shortcoming is known as the hierarchy problem and various beyond the SM solutions exist, and many predict a top quark partner to cancel the corrections to the Higgs mass exactly.

The Jung research group focusses exactly on the question of how the mass of the Higgs boson is stabilized, or to put it in more general words: how the electroweak scale is stablized. More details can be found under the following link: Research Activities.

The electroweak vacuum stability

Figure 2: The m(higgs) versus m(top) plane showing the instable, meta-stable and stable regions of the electroweak vacuum.

Figure 2: The m(higgs) versus m(top) plane showing the instable, meta-stable and stable regions of the electroweak vacuum [D0 and CMS Data added manually, plot taken from D. Buttazzo, et al., JHEP 1312 (2013) 089].

The discovery of a Higgs boson provides a crucial mile stone for the SM and for the first time allows provides a theoretical prescreption that is consistent up to highest energy scales. Hence, we can check the dependence of the Higgs quartic self-coupling \lambda on the energy scale. For reasons already discussed the top quark has a significant impact on \lambda and for top quark masses of about 175 GeV causes \lambda to be negative. However, only a positive \lambda preserves the mexican hat shaped potential, which is one of the crucial ingredients for the Higgs mechansm work as expected.

Latest measurements of the top quark mass by LHC and Tevatron experiments have reached a precision significantler smaller than 1 GeV. Figure 2 shows the latest measurement in the m(higgs) versus m(top) plane overlayed on top of the instable, meta-stable and stable regions of electroweak vacuum stability. More details can be found under the following link: Research Activities and in the selected list of the groups publications under the following link: Publications.


This research is supported by:
NSF DOE

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