This Week at Physics

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This Week at Physics

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Events During the Week of December 3rd through December 10th, 2017

Monday, December 4th, 2017

Plasma Physics (Physics/ECE/NE 922) Seminar
The Origin of Diffuse 6.4 keV line Emission from Galactic Center Molecular Clouds
Time: 12:00 pm
Place: Chamberlin 2241
Speaker: Prof. Farhad Yusef-Zadeh, Northwestern University
Abstract: The central region of our Galaxy (the inner few hundred parsecs of the Galactic center) is different from the rest of the Galaxy in its interstellar medium properties. This region is centered on a supermassive, 4 million-solar-mass black hole (Sgr A*) and is occupied by a large concentration of a warm molecular gas with high density, high velocity dispersion, high gas temperature, and high cosmic ray flux. Gas clouds in this region are subject to the strong tidal field that may suppress star formation in this region. I will give an overview of our work on the Galactic center, including the origin of the 6.4 keV line emission from molecular clouds, discovered in recent years, as well as the evidence for star formation near Sgr A*. In one model, the 6.4 keV emission results from X-ray irradiation by a hypothetical transient source associated with the massive black hole Sgr A*. Alternatively, relativistic particles from local nonthermal sources impact diffuse neutral gas producing bremsstrahlung emission and the 6.4 keV line emission.
Host: Stanislav Boldyrev
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Tuesday, December 5th, 2017

Chaos & Complex Systems Seminar
Rewards are worth the risk: Working in direct dark matter detection
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Kimberly Palladino, UW Department of Physics
Abstract: For particle physicists, determining the nature of Dark Matter is one of the greatest open mysteries. An abundance of astrophysical evidence indicates that the matter density of the universe is dominated by a new form of matter, which played a key role in growth of large scale structure. One candidate for Dark Matter is the Weakly Interacting Massive Particle (WIMP). We hope to detect WIMPS by seeing them scattering off of the target materials in our detectors. Liquid xenon has proved itself an excellent target, and LZ is a dual-phase TPC that will begin taking science data in 2020. Much of the originally proposed parameter space for WIMPS has been excluded over the past few decades, so I will also delve into the sociology of working on direct dark matter searches.
Host: Clint Sprott
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Theory Seminar (High Energy/Cosmology)
A Reappraisal on Dark Matter Co-annihilating with a Top/Bottom Partner
Time: 3:30 pm
Place: 5280 Chamberlin Hall
Speaker: Wai-Yee Keung, University of Illinois at Chicago
Abstract: tbd
Host: Vernon Barger
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Wednesday, December 6th, 2017

R. G. Herb Condensed Matter Seminar
Unconventional interactions between 2D excitons and their environment
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Dr. Andrey Klots , Vanderbilt University
Abstract: Excitons and excitonic complexes (EC) are solid-state analogs of atoms and<br>
molecules. Simple hydrogen-like states can be studied using a plain Schrodinger<br>
equation. However, when an EC is coupled to a medium with a frequency- or<br>
momentum-dependent dielectric function, "(!; q), the quantum-mechanical de-<br>
scription of such system becomes less trivial. The _rst part of this talk describes<br>
a treatment of many-body states of charged particles coupled to a frequency-<br>
dependent medium. I will show that the problem of dynamically screened ECs<br>
can be formally reduced to a simple problem of an EC in an e_ectively static<br>
medium. The environment's e_ective dielectric constant `perceived' by ECs de-<br>
pends on the symmetries of EC wavefunctions and their binding energies. This<br>
approach is applicable to individual electrons as well as to large many-body com-<br>
plexes. Predictions of environmental e_ects on EC binding were experimentally<br>
veri_ed using neutral, charged and defect-bound excitons in monolayer WS2<br>
screened by liquid, metallic and semiconducting environments.<br>
In the second part of the talk I will show that coupling of excitons to some<br>
metamaterials with momentum-dependent dielectric functions, "(~k), allows cre-<br>
ation of ultrarelativistic excitons with high momenta. As a result of the Lorentz<br>
contraction, one can observe transient one-dimensional relativistic excitons in<br>
two-dimensional graphene.<br>
Host: Lev Ioffe
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Thursday, December 7th, 2017

Astronomy Colloquium
"Black Holes in Globular Clusters"
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 pm, Talk begins at 3:45 pm
Speaker: Laura Chomiuk, Michigan State University
Abstract: Hundreds of stellar-mass black holes are expected to form in
the early lifetime of a typical globular star cluster, but the fate of these black holes remains uncertain. Are they promptly ejected from their parent clusters, or are some retained to form close binaries? The existence of black holes in globular clusters would have broad implications for the demography of black holes, the evolution of globular clusters, and gravitational wave sources. I will discuss the initial results and implications of our survey using deep radio continuum and X-ray data to search for stellar and intermediate-mass black holes in Milky Way globular clusters. I will also discuss prospects for future black-hole hunting with the next generation Very Large Array (ngVLA).
Host: Professor Eric Wilcots
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Friday, December 8th, 2017

Physics Department Colloquium
Holiday colloquium
Time: 3:30 pm
Place: 2241 Chamberlin Hall
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