Physics / Fizik

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

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Subject: search.filters.subject.Cosmological constantWoS Q: search.filters.wosQuartile.Q2

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Now showing 1 - 3 of 3
  • Article
    Citation - WoS: 10
    Citation - Scopus: 11
    Separate Einstein-Eddington Spaces and the Cosmological Constant
    (John Wiley and Sons Inc., 2016) Azri, Hemza
    Based on Eddington affine variational principle on a locally product manifold, we derive the separate Einstein space described by its Ricci tensor. The derived field equations split into two field equations of motion that describe two maximally symmetric spaces with two cosmological constants. We argue that the invariance of the bi-field equations under projections on the separate spaces, may render one of the cosmological constants to zero. We also formulate the model in the presence of a scalar field. The resulted separate Einstein-Eddington spaces maybe considered as two states that describe the universe before and after inflation. A possibly interesting affine action for a general perfect fluid is also proposed. It turns out that the condition which leads to zero cosmological constant in the vacuum case, eliminates here the effects of the gravitational mass density of the perfect fluid, and the dynamic of the universe in its final state is governed by only the inertial mass density of the fluid.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 9
    A Symmetry for the Vanishing Cosmological Constant
    (IOP Publishing Ltd., 2007) Erdem, Recai
    Two different realizations of a symmetry principle that impose a zero cosmological constant in an extra-dimensional set-up are studied. The symmetry is identified by multiplication of the metric by minus one. In the fist realization of the symmetry this is provided by a symmetry transformation that multiplies the coordinates by the imaginary number i. In the second realization this is accomplished by a symmetry transformation that multiplies the metric tensor by minus one. In both realizations of the symmetry the requirement of the invariance of the gravitational action under the symmetry selects out the dimensions given by D ≤ 2(2n + 1), n ≤ 0, 1, 2..., and forbids a bulk cosmological constant. Another attractive aspect of the symmetry is that it seems to be more promising for quantization when compared to the usual scale symmetry. The second realization of the symmetry principle is more attractive in that it is possible to make a possible brane cosmological constant zero in a simple way by using the same symmetry, and the symmetry may be identified by reflection symmetry in extra dimensions.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Single Scale Factor for the Universe From the Creation of Radiation and Matter Till the Present
    (Springer Verlag, 2014) Erdem, Recai
    A scheme for incorporating the creation of radiation and matter into the cosmological evolution is introduced so that it becomes possible to merge the times before and after the creation of radiation and matter in a single scale factor in the Robertson–Walker metric. This scheme is illustrated through a toy model that has the prospect of constituting a basis for a realistic model.