Astronomy and Astrophysics – Astrophysics – General Relativity and Quantum Cosmology
Scientific paper
2010-07-12
Astronomy and Astrophysics
Astrophysics
General Relativity and Quantum Cosmology
15 pages, LaTeX, revised version, minor change in title, section 6 and references added
Scientific paper
We show that the description of the space-time of general relativity as a diagonal four dimensional submanifold immersed in an eight dimensional hypercomplex manifold, in torsionless case, leads to a geometrical origin of the cosmological constant. The cosmological constant appears naturally in the new field equations and its expression is given as the norm of a four-vector $U$, i.e., $\Lambda=6g_{\mu\nu}U^{\mu}U^{\nu}$and where $U$ can be determined from the Bianchi identities. Consequently, the cosmological constant is space-time dependent, a Lorentz invariant scalar, and may be positive, negative or null. The resulting energy momentum tensor of the dark energy depends on the cosmological constant and its first derivative with respect to the metric. As an application, we obtain the spherical solution for the field equations. In cosmology, the modified Friedmann equations are proposed and a condition on $\Lambda$ for an accelerating universe is deduced. For a particular case of the vector $U$, we find the well known result $\Lambda\propto a(t)^{-2}$ where $a(t)$ is the scale factor.
Azri H.
Bounames A.
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