2010/03/31 by Eugene A. Lim, Ignacy Sawicki, Alexander Vikman · 1 citation
Physics and Astronomy · #astro-ph.CO #gr-qc #hep-th
paper · pdf · doi:10.1088/1475-7516/2010/05/012
published as JCAP 1005:012, 2010 · 13 pages, 3 figures. Added references, corrected language.
arxiv created 2010/04/06 · arxiv updated 2014/11/20
We introduce a novel class of field theories where energy always flows along timelike geodesics, mimicking in that respect dust, yet which possess non-zero pressure. This theory comprises two scalar fields, one of which is a Lagrange multiplier enforcing a constraint between the other's field value and derivative. We show that this system possesses no wave-like modes but retains a single dynamical degree of freedom. Thus, the sound speed is always identically zero on all backgrounds. In particular, cosmological perturbations reproduce the standard behaviour for hydrodynamics with vanishing sound speed. Using all these properties we propose a model unifying Dark Matter and Dark Energy in a single degree of freedom. In a certain limit this model exactly reproduces the evolution history of Lambda-CDM, while deviations away from the standard expansion history produce a potentially measurable difference in the evolution of structure.