
CosmoCoffee

Authors:  Richard A. Battye, Adam Moss 
Abstract:  A variety of observational tests seem to suggest that the universe is
anisotropic. This is incompatible with the standard dogma based on adiabatic,
rotationally invariant perturbations. We point out that this is a consequence
of the standard decomposition of the stressenergy tensor for the cosmological
fluids, and that rotational invariance need not be assumed, if there is elastic
rigidity in the dark energy. The dark energy required to achieve this might be
provided by point symmetric domain wall network with $P/\rho=2/3$, although
the concept is more general. We illustrate this with reference to a model with
cubic symmetry and discuss various aspects of the model. 

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Antony Lewis
Joined: 23 Sep 2004 Posts: 1351 Affiliation: University of Sussex

Posted: April 03 2006 


This is an interesting paper, which investigates whether elastic (solid) dark energy could give rise to large scale anisotropies in the observed CMB. An interesting feture is that coupling between scalar, vector and tensor modes is generated by breaking rotational invariance via the anisotropic elasticity tensor.
The model is in some tension with other (e.g. supernova) data because it requires a dark energy equation of state w=−2/3.
Their general Lagrangian is specified so that it is only a function of the metric. Since the action should be gauge invariant, and the gauge invariant function of the metric tensor is the Riemann tensor, does this mean that their model is equivalent to a generalized gravity theory with some f(R_{abcd}) action? 

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