Extending the LCDM model through shear-free anisotropies

Understand

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.