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Electroweak phase transition and LHC signatures in the singlet Majoron model

Abstract : We reconsider the strength of the electroweak phase transition in the singlet Majoron extension of the Standard Model, with a low (~TeV) scale of the singlet VEV. A strongly first order phase transition, of interest for electroweak baryogenesis, is found in sizeable regions of the parameter space, especially when the cross-coupling lambda_{hs}|S|^2|H|^2 between the singlet and the doublet Higgs is significant. Large Majorana Yukawa couplings of the singlet neutrinos, y_i S nu_i^c nu_i, are also important for strengthening the transition. We incorporate the LEP and Tevatron constraints on the Higgs masses, and electroweak precision constraints, in our search for allowed parameters; successful examples include singlet masses ranging from 5 GeV to several TeV. Models with a strong phase transition typically predict a nonstandard Higgs with mass in the range 113 GeV < m_H < 200 GeV and production cross sections reduced by mixing with the singlet, with cos^2(theta) significantly less than 1. We also find examples where the singlet is light and the decay H -> SS can modify the Higgs branching ratios relative to Standard Model expectations.
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http://hal.in2p3.fr/in2p3-00385017
Contributor : Emmanuelle Vernay <>
Submitted on : Monday, May 18, 2009 - 10:58:47 AM
Last modification on : Thursday, November 19, 2020 - 12:58:53 PM

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J.M. Cline, S. Kraml, G. Laporte, H. Yamashita. Electroweak phase transition and LHC signatures in the singlet Majoron model. Journal of High Energy Physics, Springer, 2009, 07, pp.040. ⟨10.1088/1126-6708/2009/07/040⟩. ⟨in2p3-00385017⟩

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