• Source: Two-Higgs-doublet model

The two-Higgs-doublet model (2HDM) is an extension of the Standard Model of particle physics. 2HDM models are one of the natural choices for beyond-SM models containing two Higgs doublets instead of just one. There are also models with more than two Higgs doublets, for example three-Higgs-doublet models etc.
The addition of the second Higgs doublet leads to a richer phenomenology as there are five physical scalar states viz., the CP even neutral Higgs bosons h and H (where H is heavier than h by convention), the CP odd pseudoscalar A and two charged Higgs bosons H±. The discovered Higgs boson is measured to be CP even, so one can map either h or H with the observed Higgs. A special case occurs when



cos
⁡
(
β
−
α
)
→
0


{\displaystyle \cos(\beta -\alpha )\rightarrow 0}

, the alignment limit, in which the lighter CP even Higgs boson h has couplings exactly like the SM-Higgs boson. In another limit such limit, where



sin
⁡
(
β
−
α
)
→
0


{\displaystyle \sin(\beta -\alpha )\rightarrow 0}

, the heavier CP even boson, i.e. H is SM-like, leaving h to be the lighter than the discovered Higgs; however, it is important to note that experiments have strongly pointed towards a value for



sin
⁡
(
β
−
α
)


{\displaystyle \sin(\beta -\alpha )}

that is close to 1.
Such a model can be described in terms of six physical parameters: four Higgs masses (




m


h



,

m


H



,

m


A



,

m



H


±






{\displaystyle m_{\rm {h}},m_{\rm {H}},m_{\rm {A}},m_{\mathrm {H} ^{\pm }}}

), the ratio of the two vacuum expectation values (



tan
⁡
β


{\displaystyle \tan \beta }

) and the mixing angle (



α


{\displaystyle \alpha }

) which diagonalizes the mass matrix of the neutral CP even Higgses. The SM uses only 2 parameters: the mass of the Higgs and its vacuum expectation value.
The masses of the H and A bosons could be below 1 TeV and the CMS has conducted searches around this range but no significant excess above the standard model prediction has been observed.




Classification


Two-Higgs-doublet models can introduce flavor-changing neutral currents which have not been observed so far. The Glashow-Weinberg condition, requiring that each group of fermions (up-type quarks, down-type quarks and charged leptons) couples exactly to one of the two doublets, is sufficient to avoid the prediction of flavor-changing neutral currents.
Depending on which type of fermions couples to which doublet



Φ


{\displaystyle \Phi }

, one can divide two-Higgs-doublet models into the following classes:

By convention,




Φ

2




{\displaystyle \Phi _{2}}

is the doublet to which up-type quarks couple.




See also


Alternatives to the Standard Model Higgs
Composite Higgs models
Preon




References

Kata Kunci Pencarian:

• Two-Higgs-doublet model
• Higgs boson
• Little Higgs
• Doublet–triplet splitting problem
• Composite Higgs models
• Electroweak epoch
• Higgs mechanism
• Standard Model
• Christopher T. Hill
• Custodial symmetry