Events at Physics |
Events During the Week of April 7th through April 14th, 2013
Monday, April 8th, 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
- R. G. Herb Condensed Matter Seminar
- Fluctuation effects in disordered superconducting films above Tc
- Time: 4:30 pm
- Place: 5310 Chamberlin
- Speaker: Alexander Finkelstein, Weizmann Institute of Science
- Abstract: I will report on the fluctuation corrections in homogeneously disordered superconducting films.
I will start with the Nernst and Hall Effects where fluctuation corrections can be tracked experimentally to temperatures more than order of magnitude above Tc and magnetic fields well above the upper critical field, Hc2(0). There is a quantitative agreement between our theoretical analysis and recent data obtained in conventional superconductors for the Nernst Effect (K. Behnia, France) and the Hall conductivity (Kapitulnik, Stanford) and for the Nernst Effect in certain high-Tc-family materials (L.Taillefer, Canada).
I will also report about our recent calculation of the fluctuation corrections, which is based on the Usadel equation in the real-time formulation. We adjust this approach to derive analytic expressions for the corrections to the longitudinal conductivity in the entire metallic part of the temperature-magnetic field phase diagram. This method allows us to obtain fluctuation corrections in a compact and effective way, establishing a direct connection between phenomenological and microscopic calculations. - Host: Chubukov
Tuesday, April 9th, 2013
- Chaos & Complex Systems Seminar
- Why do people believe crazy things?
- Time: 12:05 pm
- Place: 4274 Chamberlin (refreshments will be served)
- Speaker: Tim Rogers, UW Department of Psychology
- Abstract: Theories of human knowledge acquisition (ie learning) vary in many of their particulars but typically embrace the common assumption that learning is rational: through learning, people acquire reasonably accurate statistical models of the environment that allow them, given some new information, to make approximately optimal probabilistic inferences about unobserved states of the world. My own work on knowledge acquisition resides firmly in this tradition, but I have always found it difficult to reconcile this view with the everyday observation that many people appear to pretty firmly believe some pretty crazy things. We can see that this is true even without having to agree what the crazy beliefs are. For instance, the President either was or was not born in Hawaii. These are the only two logical possibilities, and there is a fact of the matter. Of the two groups prepared to vociferously argue each side of the proposition, one must be wrong. The incorrect belief persists in this group despite the fact that we all live to some extent in the same world and are presumably applying largely similar reasoning mechanisms to bear on largely the same evidence. The same point can be made with reference to controversies about global warming, evolution, whether vaccines cause autism, the efficacy of trickle-down economics or gun control policy, the relative payscales of public and private sector workers, and any number of other important issues facing public life. If we are all such optimal learners, why do people arrive at such starkly opposing sets of beliefs? There is a long tradition of research addressing aspects of this problem. One idea is that human reasoning is "motivated"--there are emotional costs associated with different beliefs, and in deciding which beliefs to endorse, people jointly minimize an error cost (ie, fit of the beliefs to evidence) and the emotional cost associated with the belief. But this approach fails to address the central question of where the emotional cost comes from, or why people should be "motivated" to entertain incorrect beliefs in the first place. A second hypothesis is that the cognitive mechanisms that support human learning and inference were only optimal in an evolutionary context, and are not suited to the modern environment in which we now find ourselves. But such accounts seem similarly underconstrained without some specific accounting of what the learning mechanisms are and how and why specifically they are unsuited to our current environment.
- Host: Sprott
Wednesday, April 10th, 2013
- Department Meeting
- Time: 12:15 pm
- Place: 5310 Chamberlin Hall
Thursday, April 11th, 2013
- R. G. Herb Condensed Matter Seminar
- The Objective Indefiniteness Interpretation of Quantum Mechanics: Partition logic, logical information theory, and quantum mechanics
- Time: 11:00 am
- Place: 5310 Chamberlin
- Speaker: David Ellerman, University of California, Riverside
- Abstract: Quantum mechanics (QM) is not compatible with the usual Boolean logic of subsets where elements have definite properties "all the way down." But there is a recently developed dual logic of partitions (subsets and partitions are category-theoretically dual) which models indefinite elements that become more definite as distinctions are made. If quantum mechanics was also incompatible with this unique dual logic of partitions, then one might "press the panic button" and postulate unknowable hidden variables to restore definiteness or soar off into the void with "many worlds" or the like.
But quantum mechanics fits perfectly with the dual logic of partitions. There is no need for (more) bizarre flights of fancy to "interpret" QM. This objective indefiniteness approach to QM does not restore our common sense assumption of definiteness down into the quantum realm. But it does restore sanity and understanding to the whole framework. That is, we now have the logic that precisely fits QM--a logic that was developed independently (i.e., without any thought of a QM connection) and that is the unique mathematical dual to ordinary Boolean subset logic, the logic assumed in classical physics. Moreover the normalized counting measure on partitions gives the quantum-relevant logical information theory--just as Boole developed logical probabilities as the normalized counting measure on subsets. Indeed, when the mathematics of partition logic and logical information theory is linearized and lifted to complex vector spaces, then it yields the mathematical framework of quantum mechanics (but not the specifically physical postulates).
The key concepts explicated by this approach are the old ideas of "objective indefiniteness" (emphasized by Abner Shimony), objective probabilities, and the objective realization of information, "its" from "dits" (= distinctions). Since partition logic, logical information theory, and the lifting program "derives" the mathematics of quantum mechanics, it shows how that QM framework can be interpreted--and this set of results gives what might be called the objective indefiniteness interpretation of quantum mechanics. - Host: Huber
- Quantum Theory Seminar
- A Common Fallacy in Quantum Mechanics: Why Delayed Choice Experiments do NOT imply Retrocausality
- Time: 2:00 pm
- Place: 5310 Chamberlin
- Speaker: David Ellerman, UC-Riverside
- Abstract: There is a common fallacy, here called the separation fallacy, that is involved in the interpretation of quantum experiments involving a certain type of separation such as the: double-slit experiments, which-way interferometer experiments, polarization analyzer experiments, Stern-Gerlach experiments, and quantum eraser experiments. It is the separation fallacy that leads not only to flawed textbook accounts of these experiments but to flawed inferences about retrocausality in the context of "delayed choice" versions of separation experiments.
- Host: Huber
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- The Fermi Large Area Telescope, Astrophysics, Dark Matter Searches and the 130GeV Line
- Time: 2:30 pm
- Place: 4274 Chamberlin
- Speaker: Eric Charles, SLAC
- Abstract: The first four and a half years of Fermi LAT operations have seen numerous exciting scientific results relating to many different topics, some expected and others unexpected. I will present a brief overview of the Fermi mission and the role it plays in current particle astrophysics research. Towards this end I will discuss some recent scientific highlights involving both galactic and extra-galactic sources classes. I will then spend the majority of the talk focusing on searches for signatures of particle dark matter interactions. In particular I will describe the LAT team's search for spectral lines from gamma-ray annihilation or decay, and discuss the status of claims of a line-like feature at 130 GeV near the Galactic center.
- Host: Neilson
- Astronomy Colloquium
- Examining Galaxy Formation and Evolution with the Milky Way and Its Satellites
- Time: 3:30 pm
- Place: 4421 Sterling Hall
- Speaker: David Nidever, University of MI
- Abstract: How galaxies form and evolve remains one of the cornerstone questions in our understanding of the universe on grand scales. The Milky Way and its satellites are a local laboratory for studying the evolution and properties of galaxies of various masses in great detail. I will highlight some recent results from three projects that are providing new insights into the structure and formation history of the Magellanic Clouds and the Milky Way. First, an extensive study of the stellar periphery of the Magellanic Clouds reveals that they are much more extended than previously thought which has implications for structure formation on small scales. Second, I have undertaken a large-scale survey to map out the gaseous Magellanic Stream. These observations provide important constraints on the orbits and
interaction history of the Magellanic Clouds with each other and the Milky Way. Finally, I will discuss SDSS-III/APOGEE, a near-infrared, high-resolution spectroscopic survey of ~100,000 stars in the Milky Way. With only the first year of data, APOGEE has already produced a number of important results especially in the Galactic bulge, with many more to come. - Host: Matt Haffner
Friday, April 12th, 2013
- Theory Seminar (High Energy/Cosmology)
- Radiatively-driven Natural Supersymmetry
- Time: 2:15 pm
- Place: 5280 Chamberlin Hall
- Speaker: Howard Baer, University of Oklahoma
- Abstract: While LHC has discovered a light Higgs boson at 125 GeV lying squarely within the predicted MSSM window, so far no sign of SUSY matter has emerged, thus requiring gluino and squark masses in the TeV-or-beyond regime. This seemingly exacerbates the Little Hierarchy Problem: why are m(Z) and m(h) ~100 GeV while sparticle masses are so heavy? We propose a conservative, model-independent measure of electroweak naturalness in supersymmetric models. Requiring finetuning at the ~10% level within the NUHM2 model, a SUSY spectrum with light higgsinos ~100-200 GeV but with TeV-scale highly mixed top squarks emerges which easily explains why m(h)~125 GeV while no sparticle signals appear at LHC8. A new SUSY signature--same-sign diboson production with minimal jet activity--emerges for LHC14. The smoking gun signature of light higgsinos are difficult to see at LHC but should be easily discovered at a linear e+e- collider, which in this case would be a higgsino, in addition to a Higgs factory. Thermally produced higgsino dark matter leaves room for axions as co-dark-matter particles. The light higgsinos should be visible at ton-scale noble liquid WIMP detectors.
- Physics Department Colloquium
- Superconductivity and the Pseudogap in theory and in copper-oxide based superconductors
- Time: 3:30 pm
- Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
- Speaker: Andrew Millis, Columbia University
- Abstract: In the "high-Tc" copper oxide materials, superconductivity is believed not to arise from the electron-phonon coupling which causes superconductivity in conventional materials such as lead or mercury and is believed to be related in some way to the physics of the correlation driven ("Mott") metal insulator transition. In this talk I will summarize what is known about the underlying physics of the materials, explain why the theoretical problem is (NP) hard and present recent theoretical and computational progress which has led to new insights into electronically mediated superconductivity.
- Host: Chubukov