Physics:Two-Higgs-doublet model
The two-Higgs-doublet model (2HDM) is an extension of the Standard Model of particle physics.[1][2] 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.[3] 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 [math]\displaystyle{ \cos(\beta - \alpha) \rightarrow 0 }[/math], the alignment limit, in which the lighter CP even Higgs boson h has couplings exactly like the SM-Higgs boson.[4] In another limit such limit, where [math]\displaystyle{ \sin(\beta - \alpha) \rightarrow 0 }[/math], 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 [math]\displaystyle{ \sin(\beta - \alpha) }[/math] that is close to 1.[5]
Such a model can be described in terms of six physical parameters: four Higgs masses ([math]\displaystyle{ m_{\rm h}, m_{\rm H}, m_{\rm A}, m_{\mathrm{H}^\pm} }[/math]), the ratio of the two vacuum expectation values ([math]\displaystyle{ \tan \beta }[/math]) and the mixing angle ([math]\displaystyle{ \alpha }[/math]) 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.[6][7]
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 [math]\displaystyle{ \Phi }[/math], one can divide two-Higgs-doublet models into the following classes:[8][9]
| Type | Description | up-type quarks couple to | down-type quarks couple to | charged leptons couple to | remarks |
|---|---|---|---|---|---|
| Type I | Fermiophobic | [math]\displaystyle{ \Phi_2 }[/math] | [math]\displaystyle{ \Phi_2 }[/math] | [math]\displaystyle{ \Phi_2 }[/math] | charged fermions only couple to second doublet |
| Type II | MSSM-like | [math]\displaystyle{ \Phi_2 }[/math] | [math]\displaystyle{ \Phi_1 }[/math] | [math]\displaystyle{ \Phi_1 }[/math] | up- and down-type quarks couple to separate doublets |
| X | Lepton-specific | [math]\displaystyle{ \Phi_2 }[/math] | [math]\displaystyle{ \Phi_2 }[/math] | [math]\displaystyle{ \Phi_1 }[/math] | |
| Y | Flipped | [math]\displaystyle{ \Phi_2 }[/math] | [math]\displaystyle{ \Phi_1 }[/math] | [math]\displaystyle{ \Phi_2 }[/math] | |
| Type III | [math]\displaystyle{ \Phi_1, \Phi_2 }[/math] | [math]\displaystyle{ \Phi_1, \Phi_2 }[/math] | [math]\displaystyle{ \Phi_1, \Phi_2 }[/math] | Flavor-changing neutral currents at tree level | |
| Type FCNC-free | [math]\displaystyle{ \Phi_1, \Phi_2 }[/math] | [math]\displaystyle{ \Phi_1, \Phi_2 }[/math] | [math]\displaystyle{ \Phi_1, \Phi_2 }[/math] | By finding a matrix pair which can be diagonalized simultaneously. [10] |
By convention, [math]\displaystyle{ \Phi_2 }[/math] is the doublet to which up-type quarks couple.
See also
References
- ↑ "Higgs Scalars and the Nonleptonic Weak Interactions", Christopher T. Hill, (1977); see pg. 100.
- ↑ Gunion, J.; H. E. Haber; G. L. Kane; S. Dawson (1990). The Higgs Hunters Guide. Addison-Wesley.
- ↑ Keus, Venus; King, Stephen F.; Moretti, Stefano (2014-01-13). "Three-Higgs-doublet models: symmetries, potentials and Higgs boson masses" (in en). Journal of High Energy Physics 2014 (1): 52. doi:10.1007/JHEP01(2014)052. ISSN 1029-8479. Bibcode: 2014JHEP...01..052K.
- ↑ Craig, N.; Galloway, J.; Thomas, S. (2013). "Searching for Signs of the Second Higgs Doublet". arXiv:1305.2424 [hep-ph].
- ↑ Collaboration, CMS (2019). "Combined measurements of Higgs boson couplings in proton–proton collisions at √s=13 TeV". The European Physical Journal C 79 (5): 421. doi:10.1140/epjc/s10052-019-6909-y. PMID 31178657.
- ↑ "Hunting the Higgs boson siblings with top quarks | CMS Experiment". https://cms.cern/news/hunting-higgs-boson-siblings-top-quarks.
- ↑ "CMS-PAS-TOP-22-010" (in en-US). https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/TOP-22-010/index.html.
- ↑ Craig, N.; Thomas, S. (2012). "Exclusive Signals of an Extended Higgs Sector". Journal of High Energy Physics 1211 (11): 083. doi:10.1007/JHEP11(2012)083. Bibcode: 2012JHEP...11..083C.
- ↑ Branco, G. C.; Ferreira, P.M.; Lavoura, L.; Rebelo, M.N.; Sher, Marc; Silva, João P. (July 2012). "Theory and phenomenology of two-Higgs-doublet models". Physics Reports (Elsevier) 516 (1): 1–102. doi:10.1016/j.physrep.2012.02.002. Bibcode: 2012PhR...516....1B.
- ↑ Botella, Francisco J.; Cornet-Gomez, Fernando; Nebot, Miguel (2018-08-30). "Flavor conservation in two-Higgs-doublet models" (in en). Physical Review D 98 (3): 035046. doi:10.1103/PhysRevD.98.035046. ISSN 2470-0010. Bibcode: 2018PhRvD..98c5046B.
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