ar X iv : g r - qc / 0 60 81 07 v 1 2 3 A ug 2 00 6 FRW UNIVERSE WITH VARIABLE G and Λ - TERMS
نویسندگان
چکیده
A new class of exact solutions of Einstein’s field equations with a perfect fluid source, variable gravitational coupling G and cosmological term Λ for FRW spacetime is obtained by considering variable deceleration parameter models for the universe. The nature of the variables G(t), Λ(t) and the energy density ρ(t) have been examined for three cases : (i) exponential (ii) polynomial and (iii) sinusoidal form. The special types of models for dust, Zel’dovich and radiating universe are also mentioned in all these cases. The behaviour of these models of the universe are also discussed in the light of recent supernovae Ia observations.
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متن کاملX iv : g r - qc / 0 60 81 04 v 3 2 9 A ug 2 00 6 Tachyons as gauge fields and the dark matters in the Universe - Tachyons compatible with causality -
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متن کاملX iv : g r - qc / 0 60 81 04 v 2 2 4 A ug 2 00 6 Tachyons as gauge fields and the dark matters in the Universe - Tachyons compatible with causality -
A tachyon field having a negative squared-masses −mt can be described in terms of infinitely degenerate massless fields. The degeneracy can be described as a gauge freedom. This picture for tachyons does not contradict causality. It is seen that the tachyons can be quenched in the Lorentz gauge, and the effects can be represented by the gauge factor. The accelerated expansion of the Universe an...
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