Can quantum effects due to a massless conformally coupled field avoid gravitational singularities?
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Tipus de documentArticle
Data publicació2012-04
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Abstract
Using quantum corrections from massless fields conformally coupled to gravity, we study the possibility of
avoiding singularities that appear in the flat Friedmann–Robertson–Walker model. We assume that the
universe contains a barotropic perfect fluid with the state equation p = ωρ, where p is the pressure and
ρ is the energy density. We study the dynamics of the model for all values of the parameter ω and also
for all values of the conformal anomaly coefficients α and β. We show that singularities can be avoided
only in the case where α > 0 and β < 0. To obtain an expanding Friedmann universe at late times
with ω > −1 (only a one-parameter family of solutions, but no a general solution, has this behavior at
late times), the initial conditions of the nonsingular solutions at early times must be chosen very exactly.
These nonsingular solutions consist of a general solution (a two-parameter family) exiting the contracting
de Sitter phase and a one-parameter family exiting the contracting Friedmann phase. On the other hand,
for ω < −1 (a phantom field), the problem of avoiding singularities is more involved because if we consider
an expanding Friedmann phase at early times, then in addition to fine-tuning the initial conditions, we
must also fine-tune the parameters α and β to obtain a behavior without future singularities: only a oneparameter
family of solutions follows a contracting Friedmann phase at late times, and only a particular
solution behaves like a contracting de Sitter universe. The other solutions have future singularities.
CitacióHaro, J. Can quantum effects due to a massless conformally coupled field avoid gravitational singularities?. "Theoretical and mathematical physics", Abril 2012, vol. 171, núm. 1, p. 563-574.
ISSN0040-5779
Versió de l'editorhttp://www.springerlink.com/content/w22566572x2705kx/fulltext.pdf
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