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Events on Thursday, April 20th, 2023

Academic Calendar
Deadline for Graduate students to request pass/fail or credit/audit options for a Spring term course
Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, URL:
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Academic Calendar
Deadline for Graduate students to change variable credits
Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, URL:
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R. G. Herb Condensed Matter Seminar
Driven-dissipative dynamics of coupled atomic clocks
Time: 10:00 am - 11:00 am
Place: 5310 Chamberlin
Speaker: Emil Yuzbashyan, Rutgers
Abstract: I will present the nonequilibrium phase diagram for the driven-dissipative dynamics of two ensembles of ultra-cold atoms coupled to a resonant cavity. We will see that this relatively simple system displays a range of remarkable phenomena beyond usual superradiance. These include periodically and quasiperiodically modulated superradiance, chaos via quasiperiodicity, and synchronized chaos.
Host: Alex Levchenko
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Preliminary Exam
Unraveling the Dynamics of the Milky Way: Investigations into the Asymmetries of the Galactic Disk
Time: 11:00 am - 1:00 pm
Place: 2124 Chamberlin or
Speaker: Lekshmi Thulasidharan, Physics Graduate Student
Abstract: "The Radcliffe wave (RW) is a recently discovered sinusoidal vertical feature of dense gas in the proximity of the Sun. In the disk plane, it is aligned with the Local Arm. However, the origin of its vertical undulation is still unknown. This study constrains the kinematics of the RW, using young stars and open clusters as tracers, and explores the possibility of this oscillation being part of a more extended vertical mode. We study the median vertical velocity trends of the young stars and clusters along with the RW and extend it further to the region beyond it. We discovered a kinematic wave in the Galaxy, distinct from the warp, with the amplitude of oscillation depending on the age of the stellar population. We performed a similar analysis in the N-body simulation of a satellite as massive as the Sagittarius dwarf galaxy impacting the galactic disk. When projected in the plane, the spiral density wave induced by the satellite impact is aligned with the RW, suggesting that both may be the response of the disk to an external perturbation. However, the observed kinematic wave is misaligned. It appears as a kinematic wave travelling radially, winding up faster than the density wave matched by the RW, setting its origins into question. If a satellite galaxy is indeed responsible for the presence of this kinematic wave, we predict the existence of a vertical velocity dipole that would be expected to form across the disk. The reality of this prediction may be measurable with the upcoming Gaia DR3 and DR4."
Host: Prof. Elena D'Onghia
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Special Plasma Seminar
The path to high-performance long-duration plasmas on Wendelstein 7-X
Time: 12:00 pm - 6:00 pm
Place: 1610 Engineering Hall
Speaker: Prof. Thomas Klinger, IPP Greifswald, Germany
Abstract: After a brief survey of the design and optimization principles of the superconducting stellarator device Wendelstein 7-X, the steps are described towards high-performance (in terms of density, temperature, confinement) and long-duration (in terms of stability, radiation, exhaust) plasmas. This is done along the lines of the present understanding of experimental observations and findings. The plasma in Wendelstein 7-X is turbulent, which has a strong impact on heat and particle transport. Methods to tame the turbulence are required for high-performance parameters. The heat and particle exhaust depends largely on the divertor functionality. The island divertor realized in Wendelstein 7-X shows allows for robust detachment and reasonable pumping. The full exploitation of Wendelstein 7-X is still in its beginnings, but the pathway towards fusion reactor relevant plasma operation becomes already visible.
Host: Benedikt Geiger
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Physics Department Colloquium
Hunting for new physics at CERN : Highlights and Prospects
Time: 3:00 pm - 5:00 pm
Place: 1313 Sterling
Speaker: Niki Saoulidou, University of Athens
Abstract: First we will make a brief introduction of the most complete theory to date, the Standard Model of Particle Physics, describing elementary particles and their interactions. Then, we will mention its shortcomings and limitations in the form of tantalizing anomalies and unknowns, that strongly point to new physics, waiting to be discovered. Efforts to resolve these now and in the near future are taking place with several different running and planned experiments worldwide. In this talk we will focus on the main two general purpose experiments, ATLAS and CMS, collecting data from proton-proton collisions at the CERN Large Hadron Collider (LHC). We will review status and prospects for discovering new physics at the LHC, trying to address the aforementioned open questions, with the data collected thus far in Run II and Run III, and also the ones anticipated at the High Luminosity (HL) LHC era. First, we will describe intriguing excesses seen by the ATLAS and CMS experiments in Run II, together with their status and follow-up plans in Run III. Next, we will focus on efforts targeting new and often more complex final states probing unexplored regions of new physics space enabled by i) new approaches to select and record events at the trigger level ii) novel reconstruction and identification techniques, and iii) powerful new analysis methodologies. Finally we we will briefly discuss prospects with the HL-LHC and give an overall outlook.
Host: Kevin Black
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Astronomy Colloquium
Mapping the circumgalactic medium with Lyα emission
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Dawn Erb, University of Wisconsin, Milwaukee
Abstract: The circumgalactic medium modulates most of the key processes of galaxy evolution. Outflows powered by star formation drive gas out of galaxies and into the CGM, while new fuel for star formation may be accreted through the CGM, likely via dense, cold streams of gas. Ionizing photons that make their way out of the galaxy must also traverse the neutral hydrogen in the CGM. Because Lyα photons resonantly scatter from neutral hydrogen in the halos of galaxies, observations of Lyα emission can offer constraints on the properties of circumgalactic gas. I will present spatially extended integral field spectroscopic observations of Lyα emission in the circumgalactic medium of galaxies at z~2 from the Keck Cosmic Web Imager. In combination with new spatially resolved radiative transfer models, these data enable constraints on the kinematics and distribution of neutral hydrogen in the CGM on scales of tens of kiloparsecs.
Host: Ke Zhang
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Graduate Program Event
Disorder in the Kitaev Spin Liquid
Time: 4:00 pm - 5:00 pm
Place: 5310 Chamberlin
Speaker: Wen-Han Kao, PhD graduate student in Physics at Univ of Minnesota
Abstract: One of the long-standing open questions that recently attracted much attention is understanding how a quantum spin liquid (QSL) state responds to various forms of structural disorder that are inevitable in real materials. In the candidate compounds of the Kitaev spin liquid (KSL) system, it has been noted that quenched disorder plays a role in suppressing the long-range magnetic order but also makes the low-energy excitations puzzling. In my talk, I will introduce how the presence of vacancies and bond randomness modifies the density of states of Majorana fermion, which is one kind of fractionalized excitation of KSL. In the site-diluted model, the pileup of low-energy states leads to divergent specific heat, and the flux-sector crossover under magnetic fields provides an explanation for the puzzling experimental findings of a strong candidate material H3LiIr2O6. We also explored how the fractionalized degrees of freedom renormalize in the strong-disorder limit of bond randomness. Namely, we applied the strong-disorder renormalization group (SDRG) on the KSL system and found that strong-disorder criticality can appear differently on distinct fractionalized excitations. This points out further inquiries about the quenched disorder effects in frustrated magnetism.
Host: Jaglul Hasan/Alex Levchenko
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