Events at Physics

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Events During the Week of October 18th through October 25th, 2020

Monday, October 19th, 2020

Plasma Physics (Physics/ECE/NE 922) Seminar
Magnetic reconnection under the microscope: 3D PIC simulations of reconnecting current sheets
Time: 12:00 pm
Place: Zoom Meeting
Speaker: Dr. Ari Le, Los Alamos National Laboratory
Abstract: Magnetic reconnection under the microscope: 3D PIC simulations of reconnecting current sheets

Reconnection allows the explosive release of magnetic energy stored in plasma currents. In space plasmas, reconnection depends on the smallest electron kinetic scales. Numerical simulations, observations by NASA’s MMS spacecraft, and laboratory experiments have now all delved into these fine details. Here, recent 3D fully kinetic particle-in-cell (PIC) calculations are presented. For systems based on MMS observations of the Earth’s magnetopause, the lower hybrid drift instability (LHDI) drives anomalous particle transport. LHDI, however, does not significantly increase the reconnection rate. For conditions similar to Earth’s magnetotail, long electron current sheets supported by electron pressure anisotropy develop. The electron pressure anisotropy drives an electromagnetic instability that modulates the current density on small scales. The general structure of the extended electron current layer is nevertheless preserved, and it should therefore persist long enough to be observed both in space observations and in laboratory experiments such as TREX at WiPPL.

The ID and passcode are (Zoom):

Meeting ID: 991 5610 7574
Passcode: 883688
Host: Paul Terry
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Tuesday, October 20th, 2020

PGSC Professional Development - Science Communication
Time: 2:30 pm - 3:30 pm
Speaker: Sarah Perdue and Madeleine O'Keefe, Department of Physics & WIPAC
Abstract: Effectively communicating and publicizing your work is essential for advancing your career. In this professional development seminar, two science communication professionals from the Physics Department will join us to share their experiences. We'll discuss the most successful ways of communicating your research to non-expert and non-science audiences. Learn tips and tricks for presenting what you do to anyone in the world.
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Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
Double bang cascades from atmospheric neutrinos
Time: 3:30 pm
Speaker: Ivan Martinez-Soler , Northwestern University
Host: Baha Balantekin
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Wednesday, October 21st, 2020

Physics ∩ ML Seminar
Neural Scaling Laws and GPT-3
Time: 11:00 am - 12:15 pm
Place: Online Seminar: Please sign up for our mailing list at for zoom link
Speaker: Jared Kaplan, Johns Hopkins University
Abstract: A variety of recent works suggest that scaling laws are ubiquitous in machine learning. In particular, neural network performance obeys scaling laws with respect to the number of parameters, dataset size, and the training compute budget. I will explain these scaling laws, and argue that they are both precise and highly universal. Then I will explain how this way of thinking about machine learning led to the GPT-3 language model, and what it suggests for the future.
Host: Gary Shiu
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Department Meeting
Time: 12:15 pm - 1:30 pm
Place: Virtual see "abstract" for connection info
Speaker: Sridhara Dasu, Department Chair, UW-Madison
Meeting Coordinates: Meeting number: 120 392 9242 Password: Q5EjaTz3Pk3 (75352893 from phones) Join by video system Dial You can also dial and enter your meeting number. Join by phone +1-415-655-0001 US Toll +1-312-535-8110 United States Toll (Chicago) Access code: 120 392 9242
Host: Sridhara Dasu, Department Chair
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Thursday, October 22nd, 2020

Cosmology Journal Club
Time: 12:00 pm - 1:00 pm
Abstract: Cosmology Journal Club is back! We will be having virtual meetings this semester.

Each week, we start with a couple scheduled 15 minute talks about one's research, or an arXiv paper. The last 30 minutes will typically be open to the group for anyone to discuss an arXiv paper.

All are welcome and all fields of cosmology are appropriate.

Contact Ross Cawthon, cawthon@wisc, for more information.

Zoom info
Meeting ID: 93592708053, passcode: cmbadger

Or click:
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Evidence for the Higgs boson decays to dimuons
Time: 3:00 pm - 4:00 pm
Place: Zoom :
Speaker: Stephane Cooperstein, UCSD
Host: Sridhara Dasu
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Astronomy Colloquium
Scaling Laws for Large Scale Magnetic Fields in Stars and in the Laboratory
Time: 3:30 pm - 5:00 pm
Place: Zoom meeting(see Abstract ) Coffee and tea 3:30 pm, Talk 3:45 PM
Speaker: Ethan Visniac, John Hopkins University
Abstract: The turbulent generation of large scale magnetic fields is driven by the transport of magnetic helicity, which is robustly conserved in conducting fluids. Some simple scaling laws emerge from this. These can be extended by considering the relationship between shear and rotation in turbulent convection. This work can be directly applied to stellar magnetic fields for fully convective stars. Surprisingly, the same scaling laws seem to apply generally, even in the presence of stellar tachoclines. I will also discuss the prospects for applying these insights to laboratory experiments.

Zoom Meeting information:

Meeting ID: 817 5005 5728
Passcode: 000018
Host: Professor Alex Lazarian
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Friday, October 23rd, 2020

Graduate Introductory Seminar (Physics 701)
Semiconductor qubits
Time: 12:05 pm - 12:55 pm
Place: BBCollaborate
Speaker: Mark Eriksson, UW Madison Department of Physics
Host: Sridhara Dasu
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Theory Seminar (High Energy/Cosmology)
New roads to discovery of light states
Time: 2:00 pm - 3:00 pm
Place: For zoom link, sign up at:
Speaker: Jeff Dror, UC Berkeley
Abstract: Light particles can imprint themselves on our detectors in spectacular and often subtle ways. In this talk, I will present two new probes of hidden sectors. In the first part, I consider the prospect of seeing a relativistic background of axions, a so-called "cosmic axion background" (CaB). This background can have a range of possible cosmic sources and I consider several possible mechanisms (with the most well known being thermal production). Furthermore, I will show that with dedicated searches, a CaB may be detectable with cavity experiments such as ADMX or DM-radio. In the second part, I revisit phenomenology of leptonic gauge bosons (such as Lmu-Ltau) showing that they couple to a non-conserved current.This property can be used to show that in the high energy limit, these gauge bosons are equivalent to majorons. This allows them to be discovered using several new probes including neutrino decays, meson decays, neutrinoless double beta decay searches, and neutrino annihilations in thermal systems. These bounds drastically shape the parameter space of these theories.
Host: Lars Aalsma
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Department Coffee Hour
Time: 3:30 pm - 4:30 pm
Abstract: Join us weekly for an informal virtual coffee hour! Catch up with others in the department, tell us how things are going, and impress everyone with your Zoom background skills. Coffee Hour is open to any and all faculty, staff, and students in the department. Sometimes we have a topic, and we'll try to get that topic posted here in advance or sent out by email before each coffee hour.
Host: Department
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