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This Week at Physics

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Events During the Week of April 28th through May 5th, 2013

Monday, April 29th, 2013

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:30 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)
Host: Peter Timbie
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Tuesday, April 30th, 2013

Chaos & Complex Systems Seminar
Aldo Leopold, phenology and climate change
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Stan Temple, Nelson Institute
Abstract: Aldo Leopold, best known as the author of A Sand County Almanac, was a keen observer of the natural world. Throughout his life he kept daily journals recording observations of seasonal events, especially those occurring at his beloved "shack" on the Leopold farm which was the setting for many essays in A Sand County Almanac. Leopold's meticulous phenological observations have provided us with an unparalleled record of when plants bloomed, birds migrated and other natural events. Analyzing his historical observations of hundreds of natural events as well as recent records helps us understand how climate change is affecting the ecological community.
Host: Sprott
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Theory Seminar (High Energy/Cosmology)
Double Disk Dark Matter
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: Andrey Katz, Harvard University
Abstract: We consider a scenario that we call Partially Interacting Dark Matter (PIDM). This scenario contains self-interacting dark matter, but it is not the dominant Dark Matter component. Even if PIDM contains only a fraction of the net dark matter density, comparable to the baryonic fraction, the subdominant componentaEuroTMs interactions can lead to interesting and potentially observable consequences. Our primary focus will be the special case of Double-Disk Dark Matter (DDDM), in which self-interactions allow the dark matter to lose enough energy to lead to dynamics similar to those in the baryonic sector. We explore a simple model in which DDDM can cool einotfciently and form a disk within galaxies, and we evaluate some of the possible observational signatures. The most prominent signal of such a scenario could be an enhanced indirect detection signature with a distinctive spatial distribution. Such scenarios also predict additional dark radiation degrees of freedom that could soon be detectable and would ininot,uence the interpretation of future data, such as that from Planck and from the Gaia satellite.
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Wednesday, May 1st, 2013

No events scheduled

Thursday, May 2nd, 2013

R. G. Herb Condensed Matter Seminar
Bulk Phononic Crystal as Quantum Information Bus between Shallow Donor Spins
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Vadim Smelyanskiy, NASA, Ames Research Center
Abstract: We propose a new candidate for a spin qubit based on shallow donor spins in the semiconductor with very low isotopic concentration of nuclear spins and with spin orbital interaction many orders of magnitude stronger than that in silicon. In a uniform material this interaction leads to a short spin lifetimes. However we show that this lifetime increases dramatically when donor spin is placed in quasi-2D bulk phononic crystal (PnC) with the energy of a Zeeman splitting being inside of a complete phononic bandgap. In this situation single phonon processes are suppressed by energy conservations. We show that two-phonon decay remains very slow while virtual phonon exchange leads to a strong coupling between donor spins. We show that resonance coherent excitation transfer between the spins is enhanced exponentially when their Zeeman splitting is tuned near the phononic crystal band edge. We also show that long-range longitudinal interaction (z-z) between spins in PnC is very similar to then one mediated by Lamb waves in elastic plate. We explore various PnC cell shapes and proportions to maximize the above coherent effects and minimize the decay rate, focusing mainly on the quasi-2D square "Cross" crystal type initially proposed by Safavi-Naeini and Painter. We show that the system is a very interesting candidate for the quantum computing applications with unit cell size ~ 100-150nm.
Host: Coppersmith & Saffman
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Friday, May 3rd, 2013

Theory Seminar (High Energy/Cosmology)
Low-Mass Higgs Bosons in the NMSSM and Their LHC Implications
Time: 2:15 pm
Place: 2335 Sterling Hall
Speaker: Shufang Su, University of Arizona
Abstract: We study the Higgs sector of the Next to Minimal Supersymmetric Standard Model (NMSSM) in light of the discovery of the SM-like Higgs boson at the LHC. We perform a broad scan over the NMSSM parameter space and identify the regions that are consistent with current Higgs search results at colliders. In contrast to the commonly studied ``decoupling'' scenario in the literature where the MSSM CP-odd Higgs boson mass is large mA>>mZ, we pay particular attention to the light Higgs states in the case when mA ~ mZ. The SM-like Higgs boson could be either the lightest CP-even scalar or the second lightest CP-even scalar. These NMSSM parameter regions have unique properties and offer rich phenomenology. We evaluate the production and decay of the Higgs bosons in this model and comment on further searches at the LHC to probe the Higgs sector of the NMSSM.
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Physics Department Colloquium
2013 Alumni Award Winner
Pursuing Climate Science: From Small Particles to Large Airplanes
Time: 4:00 pm
Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
Speaker: David Fahey, Earth System Research Laboratory, National Oceanic & Atmospheric Administration
Abstract: I will present two topics to highlight how my NOAA research contributes to climate change science. First, black carbon particles play a complex role in our climate system. Refractory black carbon is the primary cause of aerosol optical absorption in the atmosphere and also changes cloud properties and snow and ice albedo. Large gaps exist in our ability to measure and model black carbon abundances and climate effects. I helped lead a recently published assessment* which is the first evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms. Second, the Global Hawk unmanned aircraft system (UAS)**, the worldaEuroTMs largest, can travel 10000 nm on 30-hr flights at altitudes up to 20 km. In an ongoing flight campaign, our principal objective is to advance understanding of processes occurring in the tropical tropopause layer related to water vapor and ice clouds. These processes control stratospheric humidity, which plays an important role in EarthaEuroTMs radiation budget and stratospheric photochemistry. The data from recent tropical flights demonstrate the great potential of Global Hawk for Earth science research. * http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50171/abstract ** http://espo.nasa.gov/missions/attrex/
Poster: http://www.physics.wisc.edu/twap/posters/2013/2672.pdf
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2013/2013-04-29.pdf

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