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| Book/Dissertation / PhD Thesis | PUBDB-2017-11438 |
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2017
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2017-11438
Report No.: DESY-THESIS-2017-041
Abstract: Supersymmetric (SUSY) theories such as the Minimal Supersymmetric Standard Model(MSSM) predict a new particle spectrum, including an extended Higgs sector, in orderto address fundamental questions that remain unanswered with the results obtained atthe Large Hadron Collider (LHC) so far. Despite an extensive programme to searchfor additional Higgs bosons at the LHC, no new Higgs-like particles have been observedbeyond the discovered signal at 125 GeV. Such searches have not taken into accountCP-violating effects in the Higgs sector, which are well-motivated in the light of the perceivedbaryon asymmetry in the universe, and which can induce significant deviations inthe phenomenology of the Higgs bosons. The search for additional Higgs bosons shouldtherefore account for the possibility that they may not necessarily be CP-eigenstates. Inthe most general case where the MSSM parameters can be complex, the three neutralHiggs bosons of the theory are the loop-corrected mass eigenstates {h1, h2, h3}, which areadmixtures of the tree-level CP-even and CP-odd Higgs states. This thesis focusses on theeffects of complex parameters on the production cross sections of these Higgs bosons andthe interference occurring between nearly mass-degenerate Higgs states. In the first partof this thesis, we discuss higher-order corrections in the Higgs sector which give rise toCP-violating mixing between the tree-level mass eigenstates, and present a computationof inclusive cross sections for the production of the CP-admixed Higgs bosons throughgluon fusion and bottom-quark annihilation. The predictions for the gluon-fusion processare based on an explicit calculation of the leading-order cross section for the generalcase of arbitrary complex parameters, supplemented by various higher-order corrections.The cross sections for the bottom-quark annihilation process are treated with a simplere-weighting procedure. In the next part, we describe the implementation of our crosssectionpredictions into an extension of the numerical code SusHi, named SusHiMi. Inour numerical analysis, we employ SusHiMi to study the effects of the phase of the softSUSY-breaking trilinear coupling of the Higgs with the top squark, and of the phaseof the gluino mass parameter on the neutral Higgs cross sections, masses, and mixings.We demonstrate that squark effects can be strongly dependent on the phases of thecomplex parameters, and emphasise the relevance of the resummation of squark effectsin the bottom-Yukawa coupling. Furthermore, we show that in a scenario where thetwo heavy Higgs bosons, h2 and h3, are strongly admixed and nearly mass-degenerate,experimentally resolving the two Higgs bosons as separate signals may not be possible.Only the sum of their cross sections including interference terms can be measured experimentally.Finally, we incorporate our cross section predictions into a formalism toaccount for the CP-violating interference between the Higgs bosons. In the prediction ofthe process b¯b ! h2, h3 ! +−, we show that strongly destructive interference arisesin the benchmark scenario defined in this thesis. Consequently, considerable parameterregions escape the exclusion bounds, which would be ruled out in LHC searches whichneglect these interference contributions.
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