Douglas Spolyar, Martin Sahlén, Joe Silk
Modified gravity has garnered interest as a backstop against dark matter and dark energy (DE). As one possible modification, the graviton can become massive, which introduces a new scalar field. The new field can lead to a nontrivial equation of state (EOS) of DE which is density-and-scale-dependent. Tension between Type Ia supernovae and Planck can possibly be reduced. In voids the new scalar field dramatically alters the EOS of DE, gives rise to a significant gravitational slip between the two metric potentials, and also develops a topological defect (a domain wall) due to a nontrivial scalar field vacuum structure.
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http://arxiv.org/abs/1304.5239
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