## Archive for December 27, 2008

### Dark Matter is a Quantum Liquid

The winter holidays provide an opportunity to read more than one normally can (and to blog more, too). This year I have come across some excellent papers already, and perhaps the most startling one was written by Bob McElrath, who is currently a research fellow at CERN.

Bob’s latest paper is called **Emergent Electroweak Gravity** (arXiv:0812.2696) – a catchy title to be sure. The paper is short but very deep, and since I am an experimenter, I am not well qualified to judge his conclusions. He recently presented this work in the Chicago area, and my theorist friends seem to find it very interesting indeed.

The paper begins with basic quantum mechanics and statistical mechanics, and quickly comes to the conclusion that startles me the most:

…today, WIMPs and at least two neutrino mass eigenstates are definitely quantum liquids.

The point is that there should be an attractive contact interaction which induces the phase transition to a super-fluid. Since collisions are very rare, the super-fluid is not disrupted. The implication is that calculations of relic densities and WIMP searches need to be revised so that the WIMPs are treated as a quantum liquid rather than a classical gas. I am not expert, but doesn’t this mean that the conventional wisdom needs serious revision, if Bob is right?

In the last third of this short paper, Bob makes some more exciting claims. He points out that a condensate will break Lorentz invariance. More specifically, Poincare invariance will be broken spontaneously and dynamically, and relic neutrino density will vary in space. This links standard model neutrino interactions with the space-time Lorentz group, and Bob identifies a generator for the broken symmetry and the associated Goldstone bosons. The field operator for the neutrino condensate and the propagating Goldstone bosons together form a 4-tensor that would be identified with the spin-2 graviton. Hence, Bob speculates, gravity arises from the standard model interactions of relic neutrinos which necessarily form a quantum super-fluid!

Again, as an experimenter I won’t judge the validity of these claims, but I will say that I find these ideas exciting. I might even venture a couple of basic questions (though not smart ones…)

- What is the impact on predictions for observing WIMPs in direct and indirect detection experiments? What about PAMELA and ATIC?
- Since Bob links gravity to standard model interactions of relic neutrinos, there will be a numerical connection between Newton’s constant and electroweak constants. Can one specify these connections, based on a model for the neutrinos and their density?
- Can we find a way to confirm the breaking of Lorentz invariance from astrophysical observations?

I am confident that Bob will write more about this in the future.

John Conway expresses similar interest in his latest entry at CosmicVariance. As he says, it would be great to read opinions from the experts…