Wednesday, October 15, 2008

Stringy H-field alternative to dark matter?

Yeuk-Kwan Edna Cheung & Feng Xu (Edna is the lady below Stephon Alexander and on the left side from Nadiya Tkachuk on this TASI 99 picture - in the bottom row, she is the second from the left, not from right) propose a radical alternative to the theory of dark matter.

The most important evidence for dark matter are the galaxy rotation curves: the most crucial part of the mainstream explanation is the profile of the density of dark matter. The two physicists propose a completely different and simpler model:
mv2 / r = qHv + m Fgrav
Here, the new term "qHv" replaces the gravitational force of dark matter. In the absence of other forces, a constant "H" makes strings rotate with a constant frequency around a point. But if I understand the indices here well, such a rotating string would have to be radially stretched from the point to infinity.

But ignore my doubts. The proportionality of their force to the velocity "v" is what is needed to change the r-dependence of the velocities similar to the Solar System to the observed LP-record-like dependence with a constant angular velocity. By adjusting one new parameter, "Omega = qH/2m", they can describe the galaxy rotation more or less equally well as a dark matter model which has 2 more parameters. I don't even have to tell you which graph is which because they look equally fine (click to zoom):

Edna and Feng present the new force as a stringy effect. They say it is the Lorentz-like (velocity-proportional) force from "H_{txy}" (xy is the galactic plane) universally acting on strings. Yes, they mean the 3-form field strength of the 2-form NS-NS B-field. I don't quite see what "m" and "q" could universally be and what unnaturally tiny value "H" has but it is surely an interesting fit.

Note that you may Hodge-dualize "H_{txy}" to "A_z" which means that the universal axion is changing in the direction transverse to the plane of the Milky Way, being different "above the galaxy" and "below the galaxy". Well, the model surely looks very strange but I don't see an immediate full proof that it is wrong (except of the vague doubts hinted above and difficulties to explain other evidence for dark matter) so I am going to look. You are invited to do the same thing.

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