Extending the LCDM model through shear-free anisotropies
  If the spacetime metric has anisotropic spatial curvature, one can afford to
expand the universe isotropically, provided that the energy-momentum tensor
satisfy a certain con- straint. This leads to the so-called shear-free metrics,
which have the interesting property of violating the cosmological principle
while still preserving the isotropy of the cosmic mi- crowave background (CMB)
radiation. In this work we show that shear-free cosmologies correspond to an
attractor solution in the space of models with anisotropic spatial curva- ture.
Through a rigorous definition of linear perturbation theory in these
spacetimes, we show that shear-free models represent a viable alternative to
describe the large-scale evo- lution of the universe, leading, in particular,
to a kinematically equivalent Sachs-Wolfe effect. Alternatively, we discuss
some specific signatures that shear-free models would imprint on the
temperature spectrum of CMB.
