Does the mere presence of "Dark Matter" mean that science has to take a second look at the The standard model of particle physics, or is string theory able to explain its existence?"

The Standard Model does an extraordinary job of explaining the vast majority of our current observations related to particle physics, making predications that have proven to be highly accurate and precisely verified. However, it is almost universally acknowledged by physicists as being incomplete; it is not the full story. The current Standard Model may well end up being to the ultimate theory of particles as Newton's view of gravity currently compares to Einstien's General Relativity – it works effectively and accurately in a broad range of situations, but is only a 'limiting case' of a more broadly applicable and comprehensive theory. This doesn't mean it is wrong per se, just that it isn't quite the whole story.

The standard model does not predict dark matter, but some of the extensions to the theory that aim to go further may. For example, supersymmetry predicts that there should exist some particles that are good candidates for dark matter, specifically the neutralino. Supersymmetry has not been tested in any meaningful way as far as I know, but the Large Hadron Collider may be able to provide some more definitive answers when it fires up around mid 2008.

I'd forget, for the moment, about any dark matter predictions string theory may or may not make; even strong proponents of the theory often admit to being not quite sure what it all means. The theory is still very young, is highly untestable (for the moment, anyway), and makes a number of different predictions in any one of it's many guises. This is not to say that it isn't a highly worthwhile area of ongoing study – just that it isn't mature enough yet to start taking toooo seriously.

But I still consider it a leap to name the unknown something 'dark matter" and then assert "we know it's there." NO WE DON'T. What we know is that our current models don't explain the observations, and one explanation that would certainly work is: "There's matter which we cannot see." That's not the only possible explanation.

Another explanation is that gravity waves have modulations like EM waves, and the modulations cause interractive interference patterns which reinforce or cancel each other, depending on their interaction. Opposed energies cancelling each other would, during their expansion, contain scalar quanta of energy, which would affect the surrounding spacetime, but would then be cancelled by an opposing modulation, leaving spacetime to snap-back to it's original shape, dragging everything else along with it. This effect could look like a kind of "space-time" surface tension. Consider that empty space apparently has a slight negative energy (which it shouldn't) and this explanation becomes even more intriguing.

And that's one of hundreds of possibilities besides "unidentified, invisible particles."

There's something causing the effects we observe. Let's first admit that we do not know what it is, or whether it's dark, or matter at all. It could just be a previously uncalculated property of spacetime.

What DAMA sees is a change in its background detections, annually, as the Earth goes around the Sun. Any ideas on what's causing this annual modulation, or only word that whatever it is, it ain't those WIMPy particles?