Motivated by claims of broken rotational invariance in the WMAP data, a number of models have appeared in the literature realizing this effect through vector field(s) with a nonvanishing spatial vacuum expectation value. We discuss why many such models have ghost instabilities.
Bibliographical noteFunding Information:
This work was supported in part by the US Department of Energy (Grant No. DE-FG02-94ER-40823).
- broken rotational invariance
- ghost instability