Sudden cosmological singularities in Aether scalar-tensor theories
arxiv(2024)
摘要
In this work we analyze the possibility of sudden cosmological singularities,
also known as type-II singularities, in the background of a
Friedmann-Lemaître-Robertson-Walker (FLRW) geometry in an extension of
General Relativity (GR) known as Aether scalar-tensor theories (AeST).
Similarly to several scalar-tensor theories, we observe that sudden
singularities may occur in certain AeST models at the level of the second-order
time derivative of the scale factor. These singularities can either be induced
by AeST's scalar field itself in the absence of a fluid matter component, or by
a divergence of the pressure component of the fluid. In the latter case, one
observes that the second-order time derivative of the scalar field Q is also
divergent at the instant the sudden singularity happens. We show that the
sudden singularities can be prevented by an appropriate choice of the action,
for which a divergence in the scalar field compensates the divergence in the
pressure component of the matter fluid, thus preserving the regularity of the
scale factor and all its time derivatives. For the models featuring a sudden
singularity in the second-order time derivative of the scale factor, an
analysis of the cosmographic parameters, namely the Hubble and the deceleration
parameters, indicates that cosmological models featuring sudden singularities
are allowed by the current cosmological measurements. Furthermore, an analysis
of the jerk parameter favours cosmological models that attain a sudden
singularity at a faster rate, up to a time of at most t_s∼ 1.2 t_0, where
t_0 is the current age of the universe, and with negative values for the
cosmological snap parameter.
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