Two-Higgs-doublet model

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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 , 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 , 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 that is close to 1.[5]

Such a model can be described in terms of six physical parameters: four Higgs masses (), the ratio of the two vacuum expectation values () and the mixing angle () 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

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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  , 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       charged fermions only couple to second doublet
Type II MSSM-like       up- and down-type quarks couple to separate doublets
X Lepton-specific      
Y Flipped      
Type III       Flavor-changing neutral currents at tree level
Type FCNC-free       By finding a matrix pair which can be diagonalized simultaneously. [10]

By convention,   is the doublet to which up-type quarks couple.

See also

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References

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  1. ^ "Higgs Scalars and the Nonleptonic Weak Interactions", Christopher T. Hill, (1977); see pg. 100.
  2. ^ Gunion, J.; H. E. Haber; G. L. Kane; S. Dawson (1990). The Higgs Hunters Guide. Addison-Wesley.
  3. ^ Keus, Venus; King, Stephen F.; Moretti, Stefano (2014-01-13). "Three-Higgs-doublet models: symmetries, potentials and Higgs boson masses". Journal of High Energy Physics. 2014 (1): 52. arXiv:1310.8253. Bibcode:2014JHEP...01..052K. doi:10.1007/JHEP01(2014)052. ISSN 1029-8479. S2CID 118482476.
  4. ^ Craig, N.; Galloway, J.; Thomas, S. (2013). "Searching for Signs of the Second Higgs Doublet". arXiv:1305.2424 [hep-ph].
  5. ^ 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. arXiv:1809.10733. doi:10.1140/epjc/s10052-019-6909-y. PMC 6528832. PMID 31178657.
  6. ^ "Hunting the Higgs boson siblings with top quarks | CMS Experiment". cms.cern. Retrieved 2023-09-02.
  7. ^ "CMS-PAS-TOP-22-010". cms-results.web.cern.ch. Retrieved 2023-09-02.
  8. ^ Craig, N.; Thomas, S. (2012). "Exclusive Signals of an Extended Higgs Sector". Journal of High Energy Physics. 1211 (11): 083. arXiv:1207.4835. Bibcode:2012JHEP...11..083C. doi:10.1007/JHEP11(2012)083. S2CID 119312000.
  9. ^ 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. 516 (1). Elsevier: 1–102. arXiv:1106.0034. Bibcode:2012PhR...516....1B. doi:10.1016/j.physrep.2012.02.002. S2CID 119214990.
  10. ^ Botella, Francisco J.; Cornet-Gomez, Fernando; Nebot, Miguel (2018-08-30). "Flavor conservation in two-Higgs-doublet models". Physical Review D. 98 (3): 035046. arXiv:1803.08521. Bibcode:2018PhRvD..98c5046B. doi:10.1103/PhysRevD.98.035046. ISSN 2470-0010.