Quantum effects, soft singularities and the fate of the universe in a braneworld cosmology

Details Quantum effects, soft singularities and the fate of the universe in a braneworld cosmology Quantum effects, soft singularities and the fate of the universe in a braneworld cosmology

2005-10-24

arxiv.org/abs/gr-qc/0510104v2

Class.Quant.Grav.23:3259-3274,2006

Astronomy and Astrophysics

Astrophysics

General Relativity and Quantum Cosmology

19 pages, 3 figures, text slightly improved and references added. Accepted for publication in Classical and Quantum Gravity

Scientific paper

10.1088/0264-9381/23/10/001

We examine a class of braneworld models in which the expanding universe encounters a "quiescent" future singularity. At a quiescent singularity, the energy density and pressure of the cosmic fluid as well as the Hubble parameter remain finite while all derivatives of the Hubble parameter diverge (i.e., ${\dot H}$, ${\ddot H}$, etc. $\to \infty$). Since the Kretschmann invariant diverges ($R_{iklm}R^{iklm} \to \infty$) at the singularity, one expects quantum effects to play an important role as the quiescent singularity is approached. We explore the effects of vacuum polarization due to massless conformally coupled fields near the singularity and show that these can either cause the universe to recollapse or, else, lead to a softer singularity at which $H$, ${\dot H}$, and ${\ddot H}$ remain finite while ${\dddot H}$ and higher derivatives of the Hubble parameter diverge. An important aspect of the quiescent singularity is that it is encountered in regions of low density, which has obvious implications for a universe consisting of a cosmic web of high and low density regions -- superclusters and voids. In addition to vacuum polarization, the effects of quantum particle production of non-conformal fields are also likely to be important. A preliminary examination shows that intense particle production can lead to an accelerating universe whose Hubble parameter shows oscillations about a constant value.

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