WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7150

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End date: 2009Institution Author: search.filters.institutionAuthor.Demir, Durmuş Ali

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Now showing 1 - 10 of 24
  • Article
    Citation - WoS: 11
    Citation - Scopus: 11
    General Tensor Lagrangians From the Gravitational Higgs Mechanism
    (IOP Publishing Ltd., 2009) Demir, Durmuş Ali; Pak, Namık Kemal
    The gravitational Higgs mechanism proposed by 't Hooft in arXiv:0708.3184 involves the spacetime metric gμv as well as the induced metric ḡμν oc ηab∂μΦ a∂νφb where φ(a = 0,..., 3), as we call it, break all four diffeomorphisms spontaneously via the vacuum expectation values (φa) ∝ xa. In this framework, we construct and analyze the most general action density in terms of various invariants involving the curvature tensors, connexion coefficients, and the contractions and the determinants of the two metric fields. We show that this action admits a consistent expansion about the flat background such that the resulting Lagrangian possesses several novel features not found in the linearized Einstein-Hilbert Lagrangian with FierzPauli mass term (LEHL-FP): (i) its kinetic part generalizes that of LELHL-FP by weighing the corresponding structures with certain coefficients generated by invariants, (ii) the entire Lagrangian is ghost- and tachyon-free for mass terms not necessarily in the Fierz-Pauli form, and, (iii) a consistent mass term is generated with no apparent need to higher derivative couplings.
  • Article
    Citation - WoS: 9
    Citation - Scopus: 10
    Doubly Charged Higgsinos at the Tevatron
    (American Physical Society, 2009) Demir, Durmuş Ali; Frank, Mariana; Ghosh, Dilip Kumar; Huitu, Katri; Rai, Santosh Kumar; Turan, İsmail
    Several 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: 7
    Citation - Scopus: 8
    Search for Gauge Extensions of the Mssm at the Lhc
    (American Physical Society, 2009) Ahmed, Ali; Demir, Durmuş Ali; Frank, Mariana; Turan, İsmail
    The extensions of the minimal supersymmetric model (MSSM), driving mainly from the need to solve the μ problem, involve novel matter species and gauge groups. These extended MSSM models can be searched for at the LHC via the effects of the gauge and Higgs bosons or their fermionic partners. Traditionally, the focus has been on the study of the extra forces induced by the new gauge and Higgs bosons present in such models. An alternative way of studying such effects is through the superpartners of matter species and the gauge forces. We thus consider a U(1)′ gauge extension of the MSSM, and perform an extensive study of the signatures of the model through the production and decays of the scalar quarks and gluino, which are expected to be produced copiously at the LHC. After a detailed study of the distinctive features of such models with regard to the signatures at the LHC, we carry out a detailed Monte-Carlo analysis of the signals from the process pp→nleptons+mjets+E T, and compare the resulting distributions with those predicted by the MSSM. Our results show that the searches for the extra gauge interactions in the supersymmetric framework can proceed not only through the forces mediated by the gauge and Higgs bosons but also through the superpartner forces mediated by the gauge and Higgs fermions. Analysis of the events induced by the squark/gluino decays presented here is complementary to the direct Z′ searches at the LHC.
  • Conference Object
    Phenomenological Aspects of U(1)' Models
    (American Institute of Physics, 2009) Demir, Durmuş Ali
    This talk summarizes certain phenomenological aspects of the supersymmetric models with an extra U(1) invariance broken at the TeV scale. The discussions involve the Higgs sector, CP violation, Neutrino masses and the LHC signatures.
  • Article
    Citation - WoS: 35
    Citation - Scopus: 37
    Dirac Neutrino Masses From Generalized Supersymmetry Breaking
    (American Physical Society, 2008) Demir, Durmuş Ali; Everett, Lisa L.; Langacker, Paul
    We demonstrate that Dirac neutrino masses in the experimentally preferred range are generated within supersymmetric gauge extensions of the standard model with a generalized supersymmetry breaking sector. If the superpotential neutrino Yukawa terms are forbidden by the gauge symmetry [such as a U(1)′], sub-eV scale effective Dirac mass terms can arise at tree level from hard supersymmetry breaking Yukawa couplings, or at one loop due to nonanalytic soft supersymmetry breaking trilinear scalar couplings. The radiative neutrino magnetic and electric dipole moments vanish at one-loop order.
  • Article
    Citation - WoS: 21
    Citation - Scopus: 22
    Vacuum Energy as the Origin of the Gravitational Constant
    (Springer Verlag, 2009) Demir, Durmuş Ali
    We develop a geometro-dynamical approach to the cosmological constant problem (CCP) by invoking a geometry induced by the energy-momentum tensor of vacuum, matter and radiation. The construction, which utilizes the dual role of the metric tensor that it structures both the spacetime manifold and energy-momentum tensor of the vacuum, gives rise to a framework in which the vacuum energy induced by matter and radiation, instead of gravitating, facilitates the generation of the gravitational constant. The non-vacuum sources comprising matter and radiation gravitate normally. At the level of classical gravitation, the mechanism deadens the CCP yet quantum gravitational effects, if strong, can keep it existent.
  • Conference Object
    Introduction To Higgs Sector: Theory and Phenomenology
    (Springer Verlag, 2008) Demir, Durmuş Ali
    This review is based on lectures delivered at International Summer School on High Energy Physics, in Akyaka, Mugla, Turkey, September 2006. The goal of the review is to introduce junior graduate students, having a some knowledge of field theory, to the problem of mass generation and its physical consequences. The review starts with the statements and a toy model of mass generation in Sect. 2. In Sect. 3 a model of weak interactions is constructed and its predictions are compared with experimental results obtained so far. Given in Sect. 4 is search strategies for Higgs boson, the only remnant of the mechanism that gives mass to matter, by referring to model predictions and experimental facilities. Finally, in Sect. 5, given are a summary of results plus reasons for and expectations from models which rehabilitate the minimal model constructed in Sect. 3.
  • Conference Object
    Signatures of Doubly-Charged Higgsinos at Colliders
    (American Institute of Physics, 2008) Demir, Durmuş Ali; Frank, Mariana; Huitu, Katri; Rai, Santosh Kumar; Turan, İsmail
    Several supersymmetric models with extended gauge structures predict light doubly-charged Higgsinos. Their distinctive signature at the large hadron collider is highlighted by studying its production and decay characteristics.
  • Article
    Citation - WoS: 18
    Citation - Scopus: 18
    Squark Pair Production in the Mssm With Explicit Cp Violation
    (American Physical Society, 2007) Alan, Ahmet T.; Cankoçak, Kerem; Demir, Durmuş Ali
    We 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: 14
    Citation - Scopus: 15
    Cern Lep Indications for Two Light Higgs Bosons and the U(1)' Model
    (American Physical Society, 2006) Demir, Durmuş Ali; Solmaz, Levent; Solmaz, Saime
    Reanalyses 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.