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This Week at Physics

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Events During the Week of November 17th through November 23rd, 2013

Monday, November 18th, 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:
    http://cmb.physics.wisc.edu/journal/index.html
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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Condensed Matter Theory Group Seminar
Tunnel-Fluctuoscopy: Fluctuation Induced Low-Bias Anomaly
Time: 4:30 pm
Place: Chamberlin 5310
Speaker: Andrey Varlamov, CNR-SPIN, Rome, Italy
Abstract: Electron tunneling spectroscopy pioneered by Esaki and Giaever offers a powerful tool for studying electronic spectra in superconductors. The phenomenological theory by Giaever and Megerle related the tunneling current to the electronic densities of states and to the difference of their equilibrium distribution functions in electrodes. This led to impressive discoveries having revealed, in particular, of the wide, pseudogap in the tunneling spectrum of superconductors above their critical temperatures. However, it turns that this standard approach is insufficient to reveal the nontrivial, related to Andreev reflection of the tunneling electrons from superconducting fluctuation domains in the biased electrode, zero-bias anomaly carrying important information about the scattering, interactions, and decoherence. Here, operating in frameworks of the microscopic theory of tunneling, we report the existence of a such low-energy singularity in a tunneling conductivity of N-I-N(S) junction directly indicating on the presence of fluctuating Cooper pairs. Our findings mark a radical departure from the conventional picture of the ZBA and open new horizons for quantitative analysis of electronic spectra of superconductors in fluctuation regime.
Host: Maxim Vavilov
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Tuesday, November 19th, 2013

Chaos & Complex Systems Seminar
A historical introduction to quantum computing
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Marty Lichtman, UW Department of Physics
Abstract: The quantum computer is on the horizon. If a system is small enough and isolated enough, it behaves according to the weird laws of quantum mechanics. One of the beautiful behaviors of a quantum system is that it can exist in a "superposition" of multiple states, at the same time. In the last two decades, physicists, including the 2012 Nobel laureates, have learned to control these systems. If we think of the state of these systems as a piece of information, we can store a superposition of data. Then by manipulating the system, a calculation is performed. The power of this quantum computation is that many calculations may effectively be performed at the same time. The potential speedup is immense. A functional quantum computer will certainly bring advances in cryptography, search, and physical simulation, and likely in all areas of science that have hard computational problems. This talk will present the development of the quantum computer in the historical context of classical computing. We will discuss the basics of how a quantum computer can speed up certain calculations, and also look at one experimental attempt to build a quantum computer using trapped neutral atoms here at UW-Madison.
Host: Clint Sprott
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Theory Seminar (High Energy/Cosmology)
Detecting dark Matter sub halos with Gaia
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: Douglas Spolyar, Institut d’astrophysique de Paris
Abstract: Cold Dark Matter (CDM) theory, a pillar of modern cosmology and astrophysics, predicts the existence of a large number of starless dark matter halos surrounding the Milky Way (MW). However, clear observational evidence of these "dark" substructures remains elusive. Here, we present a detection method based on the small, but detectable, velocity changes that an orbiting substructure imposes on the stars in the MW disk. Using high-resolution numerical simulations we estimate that the new space telescope Gaia should detect the kinematic signatures of a few starless substructures provided the CDM paradigm holds. Such a measurement will provide unprecedented constraints on the primordial matter power spectrum at low-mass scales and offer a new handle onto the particle physics properties of dark matter.
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Wednesday, November 20th, 2013

Physics Educational Innovation Forum
Organization Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
Abstract: The PEI Forum is for faculty, graduate students and staff to meet informally to discuss new ideas for teaching physics. At this first meeting we will hear about two initiatives in the Dept and make plans for future meetings:
1)Social bookmarking to facilitate journal and news reading and discussion in physics classes - why, how, results - Duncan Carlsmith
2) A new tool for quantitative assessment of student problem-solving skills - Tor Odden
Host: Duncan Carlsmith and Peter Timbie
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Thursday, November 21st, 2013

R. G. Herb Condensed Matter Seminar
Probing the chiral anomaly with nonlocal transport in Weyl semimetals
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Dmytro Pesin, University of Utah
Abstract: Weyl semimetals are three-dimensional crystalline systems where pairs of bands touch at points in momentum
space, termed Weyl nodes, that are characterized by a deinotnite topological charge: the chirality. Consequently,
they exhibit the Adler-Bell-Jackiw anomaly, which in this condensed matter realization implies that application of parallel electric (E) and magnetic (B) inotelds pumps electrons between nodes of opposite chirality at a rate proportional to E*B. We argue that this pumping is measurable via nonlocal transport experiments, in the limit of weak internode scattering. Speciinotcally, we show that as a consequence of the anomaly, applying a local magnetic inoteld parallel to an injected current induces a valley imbalance that diffuses over long distances. A probe magnetic inoteld can then convert this imbalance into a measurable voltage drop far from source and drain. Such nonlocal transport vanishes when the injected current and magnetic inoteld are orthogonal, and therefore serves as a test of the chiral anomaly. Since the nodes are analogous to valley degrees of freedom in semiconductors, this suggests that valley currents in Weyl semimetals can be controlled using electric inotelds, which has potential practical aEuro~valleytronicaEuroTM applications.
Host: Perkins
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
First Evidence of High-Energy Extraterrestrial Neutrinos at IceCube
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Claudio Kooper, UW - Madison
Abstract: The spectrum of cosmic rays includes the most energetic particles ever observed. The mechanism of their acceleration and their sources are, however, still mostly unknown. Observing astrophysical neutrinos can help solve this problem. Because neutrinos are produced in hadronic interactions and are neither absorbed nor deflected, they will point directly back to their source. This talk will cover searches for high-energy neutrinos (> 100 TeV) at the IceCube neutrino observatory, which have recently produced the first evidence for a flux beyond standard expectations from neutrinos generated in the Earth's atmosphere. This includes the detection of two events with energies above 1 PeV -- the highest energy neutrinos ever observed. The current status of these astrophysical neutrino searches and prospects for the future will be discussed.

Host: Karle
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Astronomy Colloquium
Constraining the Physics of Star Formation in Galaxies Using the JVLA and GBT
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Amanda Kepley, NRAO
Abstract: Understanding how galaxies evolve requires understanding the properties of the young massive stars that mediate their structure and evolution and understanding the conditions under which these stars form. The latest generation of radio and
submillimeter telescopes are revolutionizing our ability to probe both the young massive stars and the dense molecular gas out of which they form. In this talk, I will present observations from the JVLA and GBT that demonstrate the capabilities of these telescopes and how they can tell us about the properties
of the dense gas ionized by the young massive stars in the center of a galaxy much like our own and the properties of the dense molecular gas in a starburst environment.
Host: Professor Eric Wilcots
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Outreach and Education
Chasing the Ghost Particle Premiere
Time: 7:30 pm
Place: Milwaukee Public Museum
Speaker: Prof Francis Halzen
Abstract: You are invited to the November 21 premiere of the planetarium show Chasing the Ghost Particle: From the South Pole to the Edge of the Universe, a 30-minute film about the construction and science of the IceCube Neutrino Observatory. The premiere and first run of the movie will be held at the Milwaukee Public Museum.

Professor Francis Halzen, IceCube principal investigator, will give a short introduction starting at 7:30 pm. The show will take you from the outer reaches of the universe to inside the IceCube detector, some 2,400 meters under the Antarctic ice.

Admission to the premiere is free, but seats are limited. Reserve yours today by contacting the box office at brushel@mpm.edu or 414-278-6951.
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Friday, November 22nd, 2013

Theory Seminar (High Energy/Cosmology)
The Holomorphic Higgs Portal -- General Methods for the Higgs Lagrangian
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Piyush Kumar, Yale University
Abstract: We develop a systematic and general approach to study the Effective Higgs Lagrangian in a framework in which the Higgs fields in the visible sector couple to another sector via the superpotential. The extra sector is assumed to be super-conformal in the ultra-violet (UV) but develops a mass-gap with supersymmetry breaking in the infra-red (IR) close to the TeV scale. The main technique used in the approach is that of the Operator Product Expansion (OPE). By using OPE methods, we are able to compute the parameters in the Higgs Lagrangian to quadratic order and make general statements that are applicable to many classes of models. Not only does this approach allow us to understand the traditional problems plaguing simple models from a deeper perspective, it also provides new possibilities for solutions of these problems. The methods and results of our work should be very useful in eventually constructing a fully viable electroweak-natural model of Beyond-the-Standard Model physics.
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Physics Department Colloquium
First results from the LUX dark matter experiment at the Sanford Underground Research Facility
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Daniel McKinsey, Yale University
Abstract: The LUX (Large Underground Xenon) experiment aims at the direct detection of dark matter particles via their collisions with xenon nuclei. The 350 kg two-phase dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), was cooled and filled in February 2013. Results of the first WIMP search dataset, taken during the period April to August 2013, corresponding to 85.3 live-days of data with a fiducial volume of 118 kg, are presented.
Host: Bai
Poster: http://www.physics.wisc.edu/twap/posters/2013/3109.pdf
Video: http://www.physics.wisc.edu/vod/2013/11/22.html
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