twistor59 wrote:... I've seen nT (presumably for "tensor") used for the gravitational wave equivalent.

The relevant number quoted at the

WMAP parameter summary page and in the arxiv work is called r, the ratio of tensor(gravitational) to scalar perturbations:

http://arxiv.org/PS_cache/astro-ph/pdf/0507/0507455v3.pdf wrote:Inflation predicts nearly scale-invariant spectra of primordial scalar (energy density) and tensor (gravitational wave) perturbations. What has been less clear is the precise prediction for the scalar spectral index ns and the tensor/scalar ratio r. In particular, is ns likely to be distinguishable from pure Harrison-Zel’dovich (ns = 1)? And is r likely to be large enough for the tensor perturbations to be detected (r >~ 10−2)?

crank wrote:Do their papers suppose braneworlds to have always existed, or where do they come from to begin with before the instantiation of a universe? Maybe I am looking at this incorrectly?

If a brane collision should ever result in no separation thereafter (the branes collide inelastically and remain stuck together) then this would be the end of the Universe (an 'end of the world' scenario), otherwise the cycles of the theory's postulated branes are eternal. It remains possible, in this theory, that the cosmological 'constant' was different (higher) in the remote past than it is now but the dynamics of the cycle forces the cc to small values at late times - it's a 'stable attractor' solution, without which the model would seem fine-tuned and unstable.

I am, somehow, less interested in the weight and convolutions of Einstein’s brain than in the near certainty that people of equal talent have lived and died in cotton fields and sweatshops. - Stephen J. Gould