Physics / Fizik

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

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Author: search.filters.author.Demir, Durmuş AliSubject: search.filters.subject.Scalar field theory

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  • Article
    Citation - WoS: 232
    Citation - Scopus: 233
    Inflation With Non-Minimal Coupling: Metric Vs. Palatini Formulations
    (Elsevier Ltd., 2008) Bauer, Florian; Demir, Durmuş Ali; Demir, Durmuş Ali; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    We analyze non-minimally coupled scalar field theories in metric (second-order) and Palatini (first-order) formalisms in a comparative fashion. After contrasting them in a general setup, we specialize to inflation and find that the two formalisms differ in their predictions for various cosmological parameters. The main reason is that dependencies on the non-minimal coupling parameter are different in the two formalisms. For successful inflation, the Palatini approach prefers a much larger value for the non-minimal coupling parameter than the Metric approach. Unlike the Metric formalism, in Palatini, the inflaton stays well below the Planck scale whereby providing a natural inflationary epoch. © 2008 Elsevier B.V. All rights reserved.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 10
    Non-Gravitating Scalars and Spacetime Compactification
    (Elsevier Ltd., 2006) Demir, Durmuş Ali; Puliçe, Beyhan; Puliçe, Beyhan; Demir, Durmuş Ali; 01. Izmir Institute of Technology; 04.05. Department of Pyhsics; 04. Faculty of Science
    We discuss role of partially gravitating scalar fields, scalar fields whose energy-momentum tensors vanish for a subset of dimensions, in dynamical compactification of a given set of dimensions. We show that the resulting spacetime exhibits a factorizable geometry consisting of usual four-dimensional spacetime with full Poincaré invariance times a manifold of extra dimensions whose size and shape are determined by the scalar field dynamics. Depending on the strength of its coupling to the curvature scalar, the vacuum expectation value (VEV) of the scalar field may or may not vanish. When its VEV is zero the higher-dimensional spacetime is completely flat and there is no compactification effect at all. On the other hand, when its VEV is nonzero the extra dimensions get spontaneously compactified. The compactification process is such that a bulk cosmological constant is utilized for curving the extra dimensions.