The Viability of Phantom Dark Energy: A Brief Review

In this brief review, we examine the theoretical consistency and viability of phantom dark energy. Almost all data sets from cosmological probes are compatible with dark energy of the phantom variety (i.e., equation-of-state parameter $w<-1$) and may even favor evolving dark energy, and since we expect every physical entity to have some kind of field description, we set out to examine the case for phantom dark energy as a field theory. We discuss the many attempts at frameworks that may mitigate and eliminate theoretical pathologies associated with phantom dark energy. We also examine frameworks that provide an apparent measurement $w<-1$ while avoiding the need for a phantom field theory.