Two-Higgs-doublet model

In particle physics, a two-Higgs-doublet model (2HDM) is an extension of the Standard Model in which a second Higgs doublet is added.[1]

The addition of the second Higgs doublet leads to five physical states: the CP even neutral Higgs bosons and (where is heavier than by convention), the CP odd pseudoscalar and two charged Higgs bosons . Such a model has six free parameters: four Higgs masses (), the ratio of the two vacuum expectation values () and a mixing angle ().

A special case is when , the so-called alignment limit, in which the lighter CP even Higgs boson has couplings like the Higgs boson of the Standard Model.[2]

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 , one can divide two-Higgs-doublet models into the following classes:[3][4]

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

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

References

  1. Gunion, J.; H. E. Haber; G. L. Kane; S. Dawson (1990). The Higgs Hunters Guide. Addison-Wesley.
  2. Craig, N.; Galloway, J.; Thomas, S. (2013). "Searching for Signs of the Second Higgs Doublet". arXiv:1305.2424Freely accessible.
  3. Craig, N.; Thomas, S. (2012). "Exclusive Signals of an Extended Higgs Sector". Journal of High Energy Physics. 1211: 083. arXiv:1207.4835Freely accessible. Bibcode:2012JHEP...11..083C. doi:10.1007/JHEP11(2012)083.
  4. 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. arXiv:1106.0034Freely accessible. Bibcode:2012PhR...516....1B. doi:10.1016/j.physrep.2012.02.002.
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