Posted: Mar 03, 2010 7:56 am
Geraint wrote:Well, ns is almost always used for the scalar spectral index of density perturbations, so it would be wilfully confusing to use the same notation for the spectral index of gravity waves. I think in the original snippets they must be talking about curvature perturbations (well, I'm pretty sure, since their mention of the prediction for ns from simple models of inflation seems to tally with what I remember from elsewhere).
Thanks, yes I had a quick Google around - as you say, ns seems to be used, as far as I can tell, in connection with perturbations of the scalar curvature about the uniform curvature that you'd have in the standard FRW models. I've seen nT (presumably for "tensor") used for the gravitational wave equivalent.