Martin, Stephen P. (Professor)
Ph.D. (Doctor of Philosophy)
Department of Physics
Standard model (Nuclear physics); Phenomenological theory (Physics)
The ATLAS and CMS experiments at the Large Hadron Collider (LHC) have confirmed the existence of the Higgs boson, the last missing piece of the Standard Model, making this era a great time to look for beyond Standard Model physics, which can explain the deficiencies in the Standard Model. The research described here is highly motivated by supersymmetry, which appears as an extension of the Standard Model. The phenomenological consequences of that are of great importance and have been reflected in this research. In the first project, the prospects for LHC discovery of a narrow resonance that decays to two Higgs bosons using the bb[macron gammagamma] final state are studied. This study is inspired by the compressed Minimal Supersymmetric Standard Model, which allows the production of stoponium (a bound state of the supersymmetric partners of the top quark and its antiquark) and its decay to Higgs boson pairs, but this study is applicable to any other di-Higgs resonance produced by gluon fusion. The cross-section needed for a 5-sigma discovery at the 14 TeV LHC for such a narrow di-Higgs resonance is estimated as a function of the integrated luminosity, using the invariant mass distributions for bb [macron] and photons. I have also found the integrated luminosity required for discovery of stoponium as a function of its mass. In my second project a viable extension of the Standard Model which incorporates vectorlike fermions near the electroweak scale has been explored. Vectorlike quarks and leptons are exotic new fermions that transform in non-chiral representations of the unbroken Standard Model gauge group. Two models are considered, in which the vectorlike leptons are weak isosinglets and isodoublets. The vectorlike leptons decay to tau leptons. I have studied the prospects for excluding or discovering vectorlike leptons using multilepton events at the LHC. If the vectorlike leptons are weak isosinglets, then discovery in multilepton states is found to be extremely challenging. The prospects for exclusion or discovery of vectorlike leptons at the LHC with existing [radical square root of] s=8 TeV data and future [radical square root] s=13 TeV data are discussed. The study of the effective potential is a very important tool to explore any physics beyond Standard Model because it tells us about vacuum stability and the relation between the Higgs vacuum expectation value and other Lagrangian parameters. In the Standard Model the effective potential gets imaginary contributions when the squared mass of the Goldstone boson is negative, and it suffers from a singularity problem when the squared mass of the Goldstone boson tends to zero. It is possible to resum the SM effective potential to remove those problems associated with Goldstone boson contributions. In my last project I have shown that one can resum the effective potential in MSSM up to two-loop order to negate the spurious contributions from the Goldstone bosons.
Kumar, Nilanjana, "Phenomenological studies of minimal extensions of standard model" (2016). Graduate Research Theses & Dissertations. 4368.
xiv, 153 pages
Northern Illinois University
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Advisors: Stephen P. Martin.||Committee members: Michael Eads; David Hedin; Lee S. Sunderlin.||Includes bibliographical references.||Includes illustrations.