Extra vectorlike matter and the lightest Higgs scalar boson mass in low-energy supersymmetry

Physical review D: Particles and fields (Impact Factor: 4.86). 02/2010; 81(3):035004-035004. DOI: 10.1103/PHYSREVD.81.035004
Source: arXiv


The lightest Higgs scalar boson mass in supersymmetry can be raised significantly by extra vectorlike quark and lepton supermultiplets with large Yukawa couplings but dominantly electroweak-singlet masses. I consider models of this type that maintain perturbative gauge coupling unification. The impact of the new particles on precision electroweak observables is found to be moderate, with the fit to Z-pole data as good or better than that of the standard model even if the new Yukawa couplings are as large as their fixed-point values and the extra vectorlike quark masses are as light as 400 GeV. I study the size of corrections to the lightest Higgs boson mass, taking into account the fixed-point behavior of the scalar trilinear couplings. I also discuss the decay branching ratios of the lightest new quarks and leptons and general features of the resulting collider signatures.

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    • "Both the charged-current [17] and the flavor changing neutral current (FCNC) [18] [19] decay processes are allowed. The ratio of the predicted rates depends on the model: in some models the FCNC process dominates [20]; in others the two modes are comparable in rate. "
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    ABSTRACT: A search for the production of a heavy B quark, having electric charge -1/3 and vector couplings to W, Z, and H bosons, is carried out using proton-proton collision data recorded at the CERN LHC by the CMS experiment, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The B quark is assumed to be pair-produced and to decay in one of three ways: to tW, bZ, or bH. The search is carried out in final states with one, two, and more than two charged leptons, as well as in fully hadronic final states. Each of the channels in the exclusive final-state topologies is designed to be sensitive to specific combinations of the B quark-antiquark pair decays. The observed event yields are found to be consistent with the standard model expectations in all the final states studied. A statistical combination of these results is performed and upper limits are set on the cross section of the strongly produced B quark-antiquark pairs as a function of the B quark mass. Lower limits on the B quark mass between 740 and 900 GeV are set at a 95% confidence level, depending on the values of the branching fractions of the B quark to tW, bZ, and bH. Overall, these limits are the most stringent to date.
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    • "In addition to the chromomagnetic coupling, the b * quark investigated here also has weak couplings, as in a general class of new physics models where new heavy particles stabilise the Higgs-boson mass at the electroweak scale [22] [23] [24] [25] [26]. In such models, the heavy quarks can have left-handed or right-handed couplings to the W boson or can be vector-like with equal strength for both couplings. "
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    ABSTRACT: The results of a search for an excited bottom-quark b* in pp collisions at sqrt(s)=7 TeV, using 4.7/fb of data collected by the ATLAS detector at the LHC are presented. In the model studied, a single b*-quark is produced through a chromomagnetic interaction and subsequently decays to a W boson and a top-quark. The search is performed in the dilepton and lepton+jets final states, which are combined to set limits on b*-quark couplings for a range of b*-quark masses. For a benchmark with unit size chromomagnetic and Standard Model-like electroweak b* couplings, b*-quarks with masses less than 870 GeV are excluded at the 95% credibility level.
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    • "We implement this detailed Higgs boson mass computational methodology on points sampled from the residual strip of model space surviving subsequent to application of the " bareminimal " constraints [12] and the simplified first-level Higgs boson mass approximation detailed in Ref. [5]. In that preliminary analysis, a formula for the Higgs masssquare shift ∆m 2 h attributable to the vector-like flippon multiplets (and also more weakly to the soft term mass approximated by M S ≃ 2M 1/2 ) is adopted that implements the leading mass scale dependencies identified in Section III of Ref. [46]. This allows us to reasonably extrapolate a detailed computation of the corrected Higgs mass across the F -SU (5) model space, isolating a narrow region of the model space supporting 123 m h 127 "
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    ABSTRACT: We establish that the light Higgs boson mass in the context of the No-Scale Flipped SU(5) GUT with TeV-scale vector-like matter multiplets (flippons) is consistent with m h =125.5±0.5 GeV in the region of the best supersymmetry (SUSY) spectrum fit to low statistics data excesses observed by ATLAS in multijet and light stop 5 fb−1 SUSY searches at the LHC7. Simultaneous satisfaction of these disparate goals is achieved by employing a minor decrease in the SU(5) partial unification scale M 32 to lower the flippon mass, inducing a larger Higgs boson mass shift from the flippon loops. The reduction in M 32, which is facilitated by a phenomenologically favorable reduction of the low-energy strong coupling constant, moreover suggests an imminently observable (e|μ)+π 0 proton decay with a central value time scale of 1.7×1034 years. At the same point in the model space, we find a lightest neutralino mass of m χ =145 GeV, which is suitable for the production of 130 GeV monochromatic gamma-rays through annihilations yielding associated Z-bosons; a signal with this energy signature has been identified within observations of the galactic center by the FERMI-LAT Space Telescope. In conjunction with direct correlations to the fate of the ATLAS multijet and light stop production channels presently being tested at the LHC8, we suggest that the reality of a 125.5 GeV Higgs boson affords a particularly rich company of specific and imminently testable associated observables.
    European Physical Journal C 08/2012; 72(12). DOI:10.1140/epjc/s10052-012-2246-0 · 5.08 Impact Factor
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