WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 16Citation - Scopus: 16Stop on Top: Susy Parameter Regions and Fine-Tuning Constraints(American Physical Society, 2014) Demir, Durmuş Ali; Ün, Cem SalihWe analyze minimal supersymmetric models in order to determine in what parameter regions with what amount of fine-tuning they are capable of accommodating the LHC-allowed top-stop degeneracy window. The stops must be light enough to enable Higgs naturalness yet heavy enough to induce a 125 GeV Higgs boson mass. These two constraints imply a large mass splitting. By an elaborate scan of the parameter space, we show that the stop-on-top scenario requires at least ΔCMSSM≃O(104) fine-tuning in the constrained minimal supersymmetric Standard Model (CMSSM). By relaxing the CMSSM parameter space with nonuniversal Higgs masses, we find that ΔNUHM1≃O(104). The CMSSM with a gravitino lightest supersymmetric particle works slightly better than the nonuniversal Higgs mass model. Compared to all these, the CMSSM with μ<0 and nonuniversal gauginos yields a much smaller fine-tuning Δμ,g≃O(100). Our results show that the gaugino sector can pave the road toward a more natural stop-on-top scenario.Article Citation - WoS: 24Citation - Scopus: 25Sneutrino Dark Matter: Symmetry Protection and Cosmic Ray Anomalies(American Physical Society, 2010) Demir, Durmuş Ali; Everett, Lisa L.; Frank, Mariana; Selbuz, Levent; Turan, İsmailWe present an R-parity conserving model of sneutrino dark matter within a Higgsphilic U(1)′ extension of the minimal supersymmetric standard model. In this theory, the μ parameter and light Dirac neutrino masses are generated naturally upon the breaking of the U(1)′ gauge symmetry. One of the right-handed sneutrinos is the lightest supersymmetric particle. The leptonic and hadronic decays of another sneutrino, taken to be the next-to-lightest superpartner, allow for a natural fit to the recent results reported by the PAMELA experiment. We perform a detailed calculation of the dark matter relic density in this scenario, and show that the model is consistent with the ATIC and Fermi LAT experiments. © 2010 The American Physical Society.Article Citation - WoS: 9Citation - Scopus: 10Doubly Charged Higgsinos at the Tevatron(American Physical Society, 2009) Demir, Durmuş Ali; Frank, Mariana; Ghosh, Dilip Kumar; Huitu, Katri; Rai, Santosh Kumar; Turan, İsmailSeveral supersymmetric models with extended gauge structures, motivated by either grand unification or by neutrino mass generation, predict light doubly charged Higgsinos. In this work we study the signals of doubly charged Higgsinos at the Tevatron in both pair- and single-production modes, and show that it is possible, especially from the events containing same-sign same-flavor isolated leptons, to disentangle the effects of doubly charged Higgsinos in the Tevatron data.Article Citation - WoS: 18Citation - Scopus: 18Squark Pair Production in the Mssm With Explicit Cp Violation(American Physical Society, 2007) Alan, Ahmet T.; Cankoçak, Kerem; Demir, Durmuş AliWe analyze effects of the CP-odd soft phases in the MSSM on the pair productions of colored superpartners in pp collisions at the LHC energies. We find that, among all pair-production processes, those of the scalar quarks in the first and second generations are particularly sensitive to the CP-odd phases, more precisely, to the phases of the gluinos and neutralinos. We compute pair-production cross sections, classify various production modes according to their dependencies on the gluino and neutralino phases, perform a detailed numerical analysis to determine individual as well as total cross sections, and give a detailed discussion of 2. electric dipole moment (EDM) bounds. We find that pair productions of first and second generation squarks serve as a viable probe of the CP violation sources in the gaugino sector of the theory even if experiments cannot determine chirality, flavor and electric charge of the squarks produced.Article Citation - WoS: 14Citation - Scopus: 15Cern Lep Indications for Two Light Higgs Bosons and the U(1)' Model(American Physical Society, 2006) Demir, Durmuş Ali; Solmaz, Levent; Solmaz, SaimeReanalyses of LEP data have shown preference to two light CP-even Higgs bosons. We discuss implications of such a Higgs boson spectrum for the minimal supersymmetric model extended by a standard model singlet chiral superfield and an additional Abelian gauge invariance [the U(1)′ model]. We, in particular, determine parameter regions that lead to two light CP-even Higgs bosons while satisfying existing bounds on the mass and mixings of the extra vector boson. In these parameter regions, the pseudoscalar Higgs is found to be nearly degenerate in mass with either the lightest or next-to-lightest Higgs boson. Certain parameters of the U(1)′ model such as the effective μ parameter are found to be significantly bounded by the LEP two light Higgs signal.Article Citation - WoS: 23Citation - Scopus: 24Signals of Doubly-Charged Higgsinos at the Cern Large Hadron Collider(American Physical Society, 2008) Demir, Durmuş Ali; Frank, Mariana; Huitu, Katri; Rai, Santosh Kumar; Turan, İsmailSeveral supersymmetric models with extended gauge structures, motivated by either grand unification or by neutrino mass generation, predict light doubly-charged Higgsinos. In this work we study productions and decays of doubly-charged Higgsinos present in left-right supersymmetric models, and show that they invariably lead to novel collider signals not found in the minimal supersymmetric model or in any of its extensions motivated by the μ problem or even in extra dimensional theories. We investigate their distinctive signatures at the Large Hadron Collider in both pair- and single-production modes, and show that they are powerful tools in determining the underlying model via the measurements at the Large Hadron Collider experiments. © 2008 The American Physical SocietyArticle Citation - WoS: 10Citation - Scopus: 12Neutralino Dark Matter in the Left-Right Supersymmetric Model(American Physical Society, 2006) Demir, Durmuş Ali; Frank, Mariana; Turan, İsmailWe study the neutralino sector of the left-right supersymmetric model. In addition to the possibilities available in the minimal supersymmetric model, the neutralino states can be superpartners of the U(1)B-L gauge boson, the neutral SU(2)R gauge boson, or of the Higgs triplets. We analyze neutralino masses and determine the parameter regions for which the lightest neutralino can be one of the new pure states. We then calculate the relic density of the dark matter for each of these states and impose the constraints coming from the ρ parameter, the anomalous magnetic moment of the muon, b→sγ, as well as general supersymmetric mass bounds. The lightest neutralino can be the bino, or the right-wino, or the neutral triplet Higgsino, all of which have different couplings to the standard model particles from the usual neutralinos. A light bino satisfies all the experimental constraints and would be the preferred dark matter candidate for light supersymmetric scalar masses, while the right-wino would be favored by intermediate supersymmetric mass scales. The neutral triplet Higgs fermion satisfies the experimental bounds only in a small region of the parameter space, for intermediate to heavy supersymmetric scalar masses.Article Citation - WoS: 12Citation - Scopus: 12Phenomenological Issues in Supersymmetry With Nonholomorphic Soft Breaking(American Physical Society, 2005) Çakır, Muammer Altan; Mutlu, Sevdiye; Solmaz, LeventWe present a through discussion of motivations for and phenomenological issues in supersymmetric models with minimal matter content and nonholomorphic soft-breaking terms. Using the unification of the gauge couplings and assuming SUSY is broken with nonstandard soft terms, we provide semianalytic solutions of the RGEs for low and high choices of tan β which can be used to study the phenomenology in detail. We also present a generic form of RGIs in mSUGRA framework which can be used to derive new relations in addition to those existing in the literature. Our results are mostly presented with respect to the conventional minimal supersymmetric model for ease of comparison.