Re: Late and Early Time Decelerations and PI

>>From Osher Doctorow

Diaz-Rivera and Pimentel (2002) give the varying coupling function
w(phi) equation:

1) w(phi) = f^(-2)[-g + 2H^2(1 + q) + Hf - (8pi rho/phi)(gamma/2 - 1) +
2k/a^2]

where q = Dtt(a)a/da(dt)^2, f is [d(phi)/dt]phi, g is Dtt(phi)/phi.

Now from the viewpoint of a second power being causal and negative
terms being causal under fairly general conditions, both f and g
actually causally in w(phi) but, and so does a via a^2 and q via
da(dt)^2. H acts causally via its square in H^2 and its multiplying
f which is causal. There might be some argument about whether a term
multiplying a causal term is necessarily causal unless it's causal from
somewhere else as in the last sentence. In any case, w(phi) turned
out to be awfully causal, which is either a remarkable coincidence or
Diaz-Rivera and Pimentel are onto something big! We'd expect a
coupling function to be causal, but this much?

I notice that the authors are in Phys. Rev. D60 (1999) and Int. J. Mod.
Phys A14 (1999). Quick, let's find out what they've been doing since!

Osher Doctorow

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