Constraints on the septet-doublet mixing models from oblique parameters

Chao-Qiang Geng, Lu-Hsing Tsai, and Yao Yu
Phys. Rev. D 91, 073014 – Published 14 April 2015

Abstract

The limitations of doublet-septet mixing models resulting from the deviations of electroweak oblique parameters ΔS and ΔT are studied. In the minimal model, the mixture of the septet η and the scalar doublet in the standard model (SM) is driven by a non-Hermitian dimension-7 operator. For a smaller bare mass of the septet, ΔS puts a stringent constraint on the mixing angle sinβ between the CP-odd neutral parts of the SM Higgs doublet and η. In general, increasing the mass of the scalar septet Mη will enhance the deviation of T from the SM, whereas it decreases the magnitude of ΔS for a larger bare mass within the range Mη400  GeV. We also examine two extended models from the ordinary doublet-septet mixture pattern. One of them is based on an inert doublet-septet mixing pattern, in which there is no vacuum expectation value for the neutral component of η and stable dark matter could naturally exist. For a benchmark point with the inner doublet mass of Mχ=250 and Mη=400  GeV in this model, the mixing coefficient is found to be less than 1.8. The other extension is constructed by imposing a doubly charged scalar mixed with the doubly charged component of the septet. Apart from the contribution by the septet-doublet admixture, ΔS is suppressed by a factor of sW2 and ΔT has a significant constraint due to the vanishing vacuum polarization of Z at the momentum transfer p2=0.

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  • Received 23 December 2014

DOI:https://doi.org/10.1103/PhysRevD.91.073014

© 2015 American Physical Society

Authors & Affiliations

Chao-Qiang Geng1,2,3,*, Lu-Hsing Tsai1,†, and Yao Yu3,‡

  • 1Chongqing University of Posts and Telecommunications, Chongqing 400065, China
  • 2Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan
  • 3Physics Division, National Center for Theoretical Sciences, Hsinchu 300, Taiwan

  • *geng@phys.nthu.edu.tw
  • lhtsai@phys.nthu.edu.tw
  • yuyao@cqupt.edu.cn

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Issue

Vol. 91, Iss. 7 — 1 April 2015

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