Physics / Fizik

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

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Publisher: search.filters.publisher.Elsevier Ltd.Subject: search.filters.subject.Space-time

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  • Article
    Citation - WoS: 14
    Citation - Scopus: 15
    A Symmetry for Vanishing Cosmological Constant: Another Realization
    (Elsevier Ltd., 2006) Erdem, Recai
    A more conventional realization of a symmetry which had been proposed towards the solution of cosmological constant problem is considered. In this study the multiplication of the coordinates by the imaginary number i in the literature is replaced by the multiplication of the metric tensor by minus one. This realization of the symmetry as well forbids a bulk cosmological constant and selects out 2 (2 n + 1)-dimensional spaces. On contrary to its previous realization the symmetry, without any need for its extension, also forbids a possible cosmological constant term which may arise from the extra-dimensional curvature scalar provided that the space is taken as the union of two 2 (2 n + 1)-dimensional spaces where the usual 4-dimensional space lies at the intersection of these spaces. It is shown that this symmetry may be realized through space-time reflections that change the sign of the volume element. A possible relation of this symmetry to the E-parity symmetry of Linde is also pointed out.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 10
    Non-Gravitating Scalars and Spacetime Compactification
    (Elsevier Ltd., 2006) Demir, Durmuş Ali; Puliçe, Beyhan
    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.