A couple of things I learned today

Today is the first day of the New Horizons in Particle Cosmology workshop, the inaugural conference of the Penn Center for Particle Cosmology. It’s going on until Monday, and I have to congratulate Justin Khoury, Bhuvnesh Jain, and Mark Trodden for putting together a hell of a program.

I learned quite a lot today, but there were two things from the afternoon session that I thought I’d share with you.

  1. Rachel Bean gave a very interesting talk on some work that she’s doing on distinguishing general relativity from other theories of gravity observationally. She describes a semi-degenerate set of parameters, R & Q. The former relates the time-time potential in the metric (Check the tags. I put this under “technical”) to the space-space component. For GR, R=1. The latter describes the strength of the gravity field for a mass perturbation of a particular size. Again, for GR, Q=1.

    Bean showed some interesting results from the latest COSMOS lensing data, as well as from the WMAP results, and found that to within the errorbars, R=1, Q=1. GR (for the moment) is safe. As the errorbars shrink, the final answer may not converge around those points.

    What’s that, you say? You remember a story that I posted a few months ago in which Bean ruled out GR. My, what a good memory you have. According to Bean, it turns out that the systematic errors reported by COSMOS were somewhat smaller than they ought to have been. With the enbiggened errorbars, the data fits nicely with GR.

  2. Even if you only have a very short memory, you’ll surely remember the rumors that I reported yesterday that the Cryogenic Dark Matter Survey might report the detection of a dark matter particle — specifically a WIMP (Weakly Interacting Massive Particle) next Friday.

    Well, Jonathan Feng of UC Irvine gave a really interesting talk on “WIMP and Related Miracles.” About 2 minutes in, he announced that his collaborators in the CDMS didn’t find dark matter. That, he said, or they are the greatest poker players on the planet. He conjectures that their December 18th talks are going to put much tighter constraints on the WIMP cross-section, but that they haven’t discovered it yet.

    Technically, this isn’t news, but merely further conjecture. Still, I thought you’d like to know.

All for now.

-Dave

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