1105.1864 (Antonio Enea Romano)

Do recent accurate measurements of $H_0$ really rule out void models as
alternatives to dark energy?    [PDF]

Antonio Enea Romano

Recent accurate measurements of $H_0$ have been claimed to be enough to rule
out void models as alternatives to dark energy. Using a local redshift
expansion for the luminosity distance and the constraint from the age of the
Universe we show that the parameters defining a general LTB model give enough
freedom to be in agreement with any value of $H_0$. The proof is based on using
$H_0$ as the fundamental length scale in terms of which to express al the other
relevant quantities determining the geometry of a LTB metric. We also
generalize the notion of central smoothness, corresponding to the requirement
that all the odd derivatives of the functions of the radial coordinates
defining the model should vanish at the center; without this smoothness
condition even derivatives of the energy density would diverge at the center.
We consider general LTB models and discuss in details the existence, uniqueness
and degeneracy of the solution of the inversion problem consisting in matching
the observations of the luminosity distance, $H_0$ and the age of the Universe,
classifying models according to the central smoothness and the presence of an
isotropic but inhomogeneous big bang. Not surprisingly, given the presence of
two free functions to determine a LTB model, we find that solutions to the IP
exist both in the smooth and not smooth case. Based on this we argue that
before LTB solutions can be conclusively ruled out as viable cosmological
models it is important to prescribe a general procedure to design them, not
limited by any special assumption for the choice of the parameters necessary to
define their geometry or functional ansatz for the shape of the inhomogeneity
profile.

View original: http://arxiv.org/abs/1105.1864