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Here are some questions which I hope you don't me asking you fellas: 1.Exactly what sort of new particles are predicted by the Randal-Sundrum theory, and are any of them predicted by any other competing theory? 2.Outside of the accelerators, what sort of astronomical observations could also be used to validate the theory? 3.Now it's heartbreaking for me to even suppose this (it's such a beautiful and elegant theory), but suppose that it turns out that Randall-Sundrum theory is not correct. A null result may not necessarily disprove it, but what sort of result may do so, or at least force us to be more skeptical?

I gotta honestly say, I'm the wrong one to ask (I'm a medium-energy particle experimentalist in training and anything involving quantum gravity lies well outside my area of knowledge) - I don't know enough about the specifics of this particular theory to honestly comment one way or the other, other than to comment that the limits of the Standard Model when it comes to incorporating gravity is indeed an area of true controversy in physics & that extra physical dimensions are needed to formulate any working quantum theory of gravity.

I can tell you that a good theorist I know did tell me of another line of experimental inquiry that you didn't include - some quantum gravity theories predict that Newtonian gravity breaks down at shorter & potentially measurable distances (when I last heard, the inverse square nature of gravitation has "only" been verified down to a distance of about 0.1 mm, some hypotheses predict that this scale is where classical gravity may start to break down). As far as the Randall-Sundrum theory goes in particular, though, I have no idea, unfortunately.

Lemme jump in, while we're waiting for the smart guys to compose their answers. The idea of these branes is that gravitons are traveling here from the other brane, where gravity is its "normal" (much stronger) self. I get the idea that when this happens, stuff from here must go to the other brane, so as to balance the cosmic books. These arrivals and departures should be, in principle, detectable. But the other brane is thought to be so close to ours (maybe one planck length, says Lisa) that the transit time is probably negligible. So if all we can detect is that everything balances, and there's no detectable moment when we've got a shortage on its way to being compensated, then we've got a null result. But I may have this all messed up. Let's wait for the experts.

Extra-dimension models in general imply higher-mode graviton resonances, corresponding to non-ground-state excitations of a graviton's Schrödinger wave function. In the (massless) ground state, one half of a graviton's Schrödinger wavelength would fit along the (invisible, orthogonal) extra dimension. (You know, the old particle-in-a-box problem from chapter 2 of whatever quantum textbook you use.) This implies the existence of a state where a full wavelength fits along that dimension, and another state with one and a half, etc. If a graviton could be kicked into one of these states by, say, a powerful enough particle collision, it would carry a momentum component along the hidden direction, which would manifest itself in our space as a mass (let the graviton itself be ever so massless in 5-dimensional reality). So as you increase the collision energy, you would see a series of gigantic resonances, occurring at the effective (i.e. 4-dimensional) masses of these states.