Physics / Fizik

Permanent URI for this collectionhttps://hdl.handle.net/11147/6

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Author: search.filters.author.Ün, Cem Salih

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Now showing 1 - 3 of 3
  • Article
    Citation - WoS: 21
    Citation - Scopus: 20
    Mass Spectrum and Higgs Profile in B - L Symmetric Ssm
    (American Physical Society, 2016) Ün, Cem Salih; Özdal, Özer
    We investigate the predictions on the mass spectrum and Higgs boson decays in the supersymmetric standard model extended by U(1)(B-L) symmetry (BLSSM). The model requires two singlet Higgs fields, which are responsible for the radiative breaking of U(1)(B-L) symmetry. It predicts degenerate right-handed neutrino masses (1.7-2.2 TeV) as well as the right-handed sneutrinos of mass less than or similar to 4 TeV. The presence of right-handed neutrinos and sneutrinos triggers the baryon and lepton number violation processes, until they decouple from the standard model particles. Besides, the model predicts rather heavy colored particles; m((t) over bar), m((h) over bar) greater than or similar to 1.5 TeV, while m((tau) over tilde) greater than or similar to 100 GeV and m((chi) over tilde1 +/-) greater than or similar to 600 GeV. Even though the implications are similar to the minimal supersymmetric standard model, BLSSM can predict another Higgs boson lighter than 150 GeV. We find that the second Higgs boson can be degenerate with the lightest charge parity (CP)-even Higgs boson of mass about 125 GeV and contribute to the Higgs decay into two photons. In addition, it can provide an explanation for the excess in h -> 4l at the mass scale similar to 145 GeV.
  • Article
    Citation - WoS: 16
    Citation - Scopus: 16
    Stop on Top: Susy Parameter Regions and Fine-Tuning Constraints
    (American Physical Society, 2014) Demir, Durmuş Ali; Ün, Cem Salih
    We 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: 3
    Citation - Scopus: 3
    Reconsidering extra time-like dimensions
    (Springer Verlag, 2006) Erdem, Recai; Ün, Cem Salih
    In this study we reconsider the phenomenological problems related to tachyonic modes in the context of extra time-like dimensions. First we reconsider a lower bound on the size of extra time-like dimensions and improve on the conclusion in the literature. Next we discuss the issues of spontaneous decay of stable fermions through tachyonic decays and disappearance of fermions due to tachyonic contributions to their self-energies. We find that the tachyonic modes due to extra time-like dimensions are less problematic than the tachyonic modes in the usual 4-dimensional setting because the most troublesome Feynman diagrams are forbidden once the conservation of momentum in the extra time-like dimensions is imposed.