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**0**

**2**

A. S. Cornell

*South Africa*

**Constraining the Couplings of a Charged**

The Standard Model (SM) of particle physics has been an incredibly successful theory which has been confirmed experimentally many times, however, it still has some short-comings. As such physicists continue to search for models beyond the SM which might explain issues such as naturalness (the hierarchy problem). Among the possible discoveries that would signal the existence of these new physics models (among several) would be the discovery of a charged

Recall that in the SM we have a single complex Higgs doublet, which through the Higgs mechanism, is responsible for breaking the Electroweak (EW) symmetry and endowing our particles with their mass. As a result we expect one neutral scalar particle (known as the Higgs boson) to emerge. Now whilst physicists have become comfortable with this idea, we have not yet detected this illusive Higgs boson. Furthermore, this approach leads to the hierarchy problem, where extreme fine-tuning is required to stabilise the Higgs mass against quadratic divergences. As such a simple extension to the SM, which is trivially consistent with all available data, is to consider the addition of extra *SU*(2) singlets and/or doublets to the spectrum of the Higgs sector. One such extension shall be our focus here, that where we have two complex Higgs doublets, the so-called Two-Higgs Doublet Models (2HDMs). Such models, after EW symmetry breaking, will give rise to a charged Higgs boson in the physical spectrum. Note also that by having these two complex Higgs doublets we can significantly modify the Flavour Changing Neutral Current (FCNC) Higgs interactions in the large tan *β* region (where tan *β* ≡ *v*2/*v*1, the ratio of the vacuum expectation values (vevs) of the two

Among the models which contain a second complex Higgs doublet one of the best motivated is the Minimal Supersymmetric Standard Model (MSSM). This model requires a second Higgs doublet (and its supersymmetric (SUSY) fermionic partners) in order to preserve the cancellation of gauge anomalies [1]. The Higgs sector of the MSSM contains two Higgs supermultiplets that are distinguished by the sign of their hypercharge, establishing an unambiguous theoretical basis for the Higgs sector. In this model the structure of the Higgs sector is constrained by supersymmetry, leading to numerous relations among Higgs masses and couplings. However, due to supersymmetry-breaking effects, all such relations are modified by loop-corrections, where the effects of supersymmetry-breaking can enter [1].

**1. Introduction**

Higgs boson.

complex doublets).

**Higgs to Heavy Quarks**

*National Institute for Theoretical Physics;*

*School of Physics, University of the Witwatersrand*


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