Renée here - liveblogging from the back of Tory 208. Today, Dan Hooper from Fermilab is giving a talk on the subject of dark matter. I'll be giving live updates as the hour progresses.
Abstract:
Over seventy years, the evidence has steadily grown that much of the Universe's mass is non-luminous. Still today, however, we have not identified what makes up this mysteriously dark substance. Many experimental programs that hope to change this are underway, including deep underground detectors, gamma-ray telescopes, neutrino and anti-matter detectors, as well as particle colliders. Each of these efforts are searching for clues of dark matter's identity. With the new technologies needed to observe these particles rapidly developing, the hunt to discover dark matter's identity is well underway.
1:16pm - Dan Hooper is setting up his computer. Heather Logan begins to introduce to the speaker. A few more people trickle in. Dan has published a book on dark matter (
Dark Cosmos: In Search of Our Universe's Missing Mass and Energy) and was a post doc at Oxford. Dan speaks.
1:17 - slide 1: A Brief History of Dark Matter. Dan explains that there has been too little luminous matter in galaxies and and clusters of galaxies for many decades and how by the end of the 1970's the existence of dark matter was obvious.
1:19 - slide 2: What is Dark Matter? There are two hypothesis': MaCHOs (Massive Compact Halo Objects) and WIMPs (Weakly Interacting Particles)
1:20 - slide 3: MaCHOs. The result of the end points of stellar evolution. Black holes, neutron stars, etc are MaCHO candidates for dark matter.
1:22 - slide 4: Problem's with MaCHO.
1:24 - slide 5: A Brief History in the WMAP Sky. Dan explains the "age of precision cosmology"
1:25 - slide 6: "The world is full of thinsg which nobody by any chance ever observes." - Sherlock Holmes
1:26 - slide 7: Dark Matter. Dan explains the dark matter imprint in the cosmic microwave background. We have never seen dark matter interact with anything but gravity. Postulate: Maybe DM doesn't exist, maybe we don't understand gravity.
1:27 - slide 8: MOdified Newtonian Dynamics (MOND). Quite succesful in explaining how galaxies behave, not clusters though. MOND cannot be applied to cosmology.
1:29 - slide 9: DM and MONDs of the Past. Dan compares DM and MOND theories.
1:30 - slide 9: Picture of a bullet cluster from NASA/Chandra Press Release Aug 21, 2006. Dan point out Baryonic matter (hot gas) and Total Mass in the image. Conclusion: Not a simple modification of gravity, it is in fact DM. The End Of MOND!/? A Challenge For MOND.
1:33 - slide 10: But what are the WIMPs?
1:33 - slide 11: The Field of Particle DM Candidates. Picture of the US electoral candidates.
1:34 - slide 12: The Thermal Abundance of Weakly Interacting Massive Particles.
1:35 - slide 13: The Weak Scale and Weakly Interacting Massive Particles. Weak interaction yields a picobond, an indication that DM originates from EW physics.
1:37 - slide 14: Supersymmetry. Symmetry between bosons and fermions - an extension of the Standard Model.
1:38 - slide 15: Why Supersymmetry? With supersymmetry, fermion and boson loops cancel each other. WIth supersymmetry, all 3 forces unify at a single energy.
1:40 - slide 16: Supersymmetric Dark Matter. Possible WIMP candidates from supersymmetry include Neutralinos and Sneutrinos, but Sneutrino was excluded by direct detection.
1:42 - slide 17: Supersymmetry at the Tevatron.
1:43 - slide 18: Supersymmetry at the LHC.
1:44 - slide 19: Astrophysical Probes of Particle DM. Direct detection and indirect detection.
1:45 - slide 20: Direct Detection.
At this point, many slides are going by explaining WIMP detection, the XENON 10 limit, WIMPs worldwide. I'll drop the slide numbering now.
1:47 - slide: Indirect Detection of DM. Wimp Annihilation, Fragmentaion/Decay, Sychrotron Radiation.
1:48 - slide: Indirect Detection with Gamma-Rays.
1:49 - slide: Gamma-Rays From the Galactic Center.
1:50 - slide: Indirect Detection With Neutrinos. High E neutrinos used. The IceCube detector is explained. It's a full cubic kilometer.
1:52 - slide :Indirect Detection With Anti-Matter. Upcoming experiments, PAMELA, AMS-02, will measure the cosmic anti-matter spectrum.
1:54 - slide: Indirect Detection With Positrons. HEAT experiment reported an excess of high-E positrons in 3 balloon flights.
1:58 - slide: Indirect Detection With Sychrotron.
2:00 - slide: WMAP As A Sychrotron Telescope. Images are shown to illustrate how WMAP images are generated. The "WMAP Haze" is explained as a 20 degree bright spot in the center of our galaxy. Very difficult to explain astrophysically.
2:04 - slide: DM in the WMAP Sky. Finkbeiner suggested that the WMAP Haze could be sychrotron from electrons/positrons produced in DM annihilations in the inner galaxy.
2:05 - slide: The Remarkable Match Of The WMAP Haze To The Signal Expected From DM. The properties described as "very vanilla".
2:07 - slide: Summary. The search for DM is very exciting, many models have been ruled out with direct detection experiments. Hard sychrotron emission from the inner galaxy observed by WMAP is a compelling signature of DM annihilations. LHC is almost certain to discover low E supersymmetry if it exists in nature, but it's hard to theorize about what will be discovered. A few years from now, our understanding of DM will almost certain be very different - either a discover is made or new ideas needed.
2:11 - Applause. Dan plugs his book, and so will we:
Check it out!2:13 - Questions are taken. What fraction of the mass of the sun would be DM? A 10th of a percent - a surprisingly small amount. Heather Logan asks a technical question. Dan breaks out the chalk.
2:16 - More applause.
Wow, that was a fast-paced and interesting talk! The Physics Society would like to thank the physics department for setting up the talk and Dan Hooper for giving such an accessible talk!
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