[astro-ph/0410680] Crossing the Phantom Divide: Dark Energy
Posted: December 17 2004
This paper provides a nice continuous scheme for constructing dark energy parameterizations that evolve from equation of state w<-1 to w>-1 (or vice versa). It works by taking two separate fluids, one with constant w<-1, and one with constant w>-1.
Question: is there actually anything unphysical about a single fluid going through w=-1? Various cases involving scalar fields seem to be problematic (e.g. astro-ph/0407107), but what about general fluids?
It seems that in general the fluid velocity [tex]v \sim \log(|t-t_c|)[/tex] where [tex]w(t_c)=-1[/tex], and so it is singular. However the heat flux [tex]q=(\rho+p)v[/tex] is perfectly regular. The density constrast [tex]\delta[/tex] seems to be continuous, even though its derivative [tex]\delta'[/tex] diverges. Are these properties unphysical?
In other words, is there anything inherently wrong with evolving a single fluid and just allowing v to become singular? (as in e.g. astro-ph/0409574, with some suitable numerical massaging)
Question: is there actually anything unphysical about a single fluid going through w=-1? Various cases involving scalar fields seem to be problematic (e.g. astro-ph/0407107), but what about general fluids?
It seems that in general the fluid velocity [tex]v \sim \log(|t-t_c|)[/tex] where [tex]w(t_c)=-1[/tex], and so it is singular. However the heat flux [tex]q=(\rho+p)v[/tex] is perfectly regular. The density constrast [tex]\delta[/tex] seems to be continuous, even though its derivative [tex]\delta'[/tex] diverges. Are these properties unphysical?
In other words, is there anything inherently wrong with evolving a single fluid and just allowing v to become singular? (as in e.g. astro-ph/0409574, with some suitable numerical massaging)