Events During the Week of September 20th through September 27th, 2026
Monday, September 21st, 2026
- Theory Seminar (High Energy/Cosmology)
- Beyond Δm²: Absolute Mass Sensitivity in Neutrino Oscillations
- Time: 11:30 am - 1:00 pm
- Place: Chamberlin 5280
- Speaker: André de Gouvêa, Northwestern University
- Abstract: Conventional wisdom says that neutrino oscillations measure only mass-squared differences and not the absolute neutrino mass scale. This is true, however, only at leading order in the expansion parameters m_i/E, the ratios of the neutrino masses m_i (i = 1, 2, 3) to the neutrino energy E. At next-to-leading order, the oscillation phase includes terms proportional to m_i^4 − m_j^4 = Δm²_ij (m_i^2 + m_j^2), and is therefore sensitive to the absolute mass scale. I discuss the next-to-leading-order corrections using a wave-packet treatment and taking into account the neutrino-production kinematics. The result can be applied to reactor neutrinos and, it turns out, the JUNO experiment is sensitive to neutrino masses of a few hundred keV.
- Host: Joshua Foster
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Waves in a Plasma Ocean: Wave-Particle Interactions Throughout the Solar System
- Time: 12:00 pm - 1:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Allison Jaynes, University of Iowa
- Abstract: All planetary and smaller bodies in our solar system are embedded in a sea of plasma, like boulders in a terrestrial ocean. Their surfaces or magnetic fields run into this ocean of space plasma, generated primarily by our Sun, and create a whole range fascinating effects as a result. Waves in interplanetary space and waves produced by solar wind-planetary interactions both initiate wave-particle interactions across a variety of scale sizes. These wave-particle interactions can fuel many phenomena: from the ‘killer electrons’ in the Van Allen radiation belts that affect spacecraft and Earth’s atmosphere to the echoes of distant magnetic structures we can observe at the edge of our solar system and beyond with the Voyager spacecraft. This process can also cause the local aurora above our heads and it plays a role in the giant particle accelerator that is Jupiter’s magnetosphere. In this talk, I will present recent significant insights we’ve gained about wave-particle interactions across our solar system and illustrate how this fundamental plasma physics process underlies a vast scope of the space environment: from different worlds to the furthest reaches of our space exploration.
- Host: Vladimir Zhdankin
- WiCOR/Astronomy Monday Science Seminar
- Coda of a Dying Sun
- Time: 12:00 pm - 1:00 pm
- Place: WiCOR Space, 6515 Sterling Hall
- Speaker: Konstantin Batygin, Professor, Division of Geological & Planetary Sciences, Caltech
- Abstract: From its birth, celestial mechanics has been deeply intertwined with the question of the Solar System’s dynamical stability. For the inner planets, this question is now statistically settled: Mercury’s orbit carries roughly a 1 percent chance of destabilization before the Sun leaves the main sequence. The outer Solar System has seemed more secure, with an intrinsic dynamical lifetime estimated at approximately 10^18 years. Even accounting for solar mass loss and stellar flybys, the orbital architecture of the giant planets has been expected to persist for roughly 100 billion years.
Here, we show that these estimates rest on the assumption that solar mass loss is smooth. The recently measured recoil of white dwarfs instead points to asymmetric mass loss, most readily attributed to discrete, independently directed ejections that impulsively perturb stellar motion. As the Sun sheds its envelope in such parcels, the planetary orbits undergo a random walk whose amplitude is determined by the granularity of the mass loss. For granularity consistent with observationally permitted kicks, this stochastic forcing restructures the outer Solar System concurrently with the Sun’s death.
Our numerical experiments reveal that orbit crossing can begin on the red giant branch, with roughly 40 percent of realizations undergoing disruption or violent scattering before the white dwarf forms and roughly 90 percent self-destructing within 3 billion years. The dynamical lifetime of the outer Solar System thus collapses from approximately 10^18 years to about a billion years after white dwarf formation. - Host: WiCOR, Juliette Becker
Tuesday, September 22nd, 2026
- Preliminary Exam
- Random-Alloy Disorder Analysis in Si/SiGe Systems
- Time: 2:00 pm - 4:00 pm
- Place: 5310 Chamberlin
- Speaker: Emma Brann, Physics PhD Graduate Student
- Abstract: Si/SiGe heterostructures look promising as a scalable platform for quantum computing, but the degeneracy between the low-lying states in the silicon conduction band currently limits device fidelity. Introducing a small concentration of germanium to the quantum well offers a solution to this "valley splitting problem" by introducing random-alloy disorder. In this work, we examine the influence of this disorder in experimental results, comparing data trends and correlations against simulated and analytical results. We also present a numerical framework designed to reproduce disorder-induced errors using simulated charge stability diagrams.
- Host: Mark Friesen
- WiCOR Lecture - Fall 2026
- Planet 9 From Outer Space
- Time: 7:00 pm - 8:00 pm
- Place: Forum at the Discovery Building
- Speaker: Konstantin Batygin, Professor, Division of Geological & Planetary Sciences, Caltech
- Abstract: Over the past two decades, surveys of the outer Solar System have revealed a remarkably complex Kuiper Belt. Most of this structure can be understood through the gravitational influence of the known planets, particularly Neptune. Yet the most distant trans-Neptunian objects present several enduring puzzles: some follow elongated orbits that cluster together and remain detached from Neptune, while others occupy highly inclined or even retrograde trajectories that are difficult to produce within conventional models of Solar System evolution.
Taken together, these peculiar orbital patterns may point to the presence of an additional, as-yet-undetected planet. This object — Planet Nine — is predicted to have roughly five times the mass of Earth and to travel around the Sun on a distant, eccentric orbit with a period of approximately ten thousand years. In this talk, I will review the observational evidence that motivated the Planet Nine hypothesis, explain the dynamical mechanisms by which such a planet could sculpt the distant Solar System, and discuss current observational efforts and the prospects for its detection. - Host: WiCOR, Juliette Becker
Wednesday, September 23rd, 2026
- Thesis Defense
- Study of Argon Dissolved in Water via EXAFS Spectroscopy
- Time: 1:00 pm - 3:00 pm
- Place: Sterling B343
- Speaker: Roberta Candela , Biophysics PhD Graduate Student
- Host: Uwe Bergmann
Thursday, September 24th, 2026
- R. G. Herb Condensed Matter Seminar
- Title to be announced
- Time: 10:00 am - 11:00 am
- Place: Chamberlin 5310
- Speaker: Frank Gao, UW-Madison Chemistry
- Host: Elio Koenig-Tarasevich
- Astronomy Colloquium
- Black Hole Images: What they've taught us so far and how we can improve them
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Lia Medeiros, UW-Milwaukee
- Abstract: Horizon-scale observations of accreting supermassive black holes with the Event Horizon Telescope (EHT) have opened a new window onto strong-field gravity and black-hole accretion. The EHT's 2022 observations of Sagittarius A* (Sgr A*), the black hole at the center of our Galaxy, provide a new opportunity to test the Kerr metric in a previously unexplored regime. I will discuss the EHT observations of Sgr A*, focusing on what they can reveal about fundamental physics, and briefly compare these results with the earlier observations of M87*. I will then discuss how improvements in both observations and data analysis can extend these measurements in the near future. In particular, I will introduce PRIMO, a machine-learning algorithm for EHT data analysis that uses a large library of high-fidelity simulations as a training set. I will show a higher-resolution reconstruction of M87* obtained with PRIMO and demonstrate how improved image reconstruction can provide new constraints on both black-hole accretion and strong-field gravity.
- Host: Nicholas Stone
Friday, September 25th, 2026
- Physics Department Colloquium
- New Horizons in Black Hole Imaging
- Time: 3:30 pm - 4:30 pm
- Place: Chamberlin 2241 -
- Speaker: Charles Gammie, University of Illinois
- Abstract: Abstract: The Event Horizon Telescope has produced the first horizon-scale images of black holes at millimeter wavelengths. These images probe how black holes interact with their surroundings, how plasmas behave under extreme conditions, and how spacetime shapes the appearance of matter near an event horizon. I will review existing images, summarize what we have learned from them, and discuss the main theoretical challenges in interpreting them. I will then look ahead to black hole movies that trace the dynamics of the emitting near-horizon plasma, multi-frequency imaging, and the higher angular resolution that could be accessed with a space-based antenna.
- Host: Vladimir Zhdankin
Saturday, September 26th, 2026
- UW Madison Physics Department Picnic
- Time: 11:30 am - 1:00 pm
- Place: Rennebohm Park, 115 N Eau Claire Ave, Madison, WI 53705
- Host: Sharon Kahn
Sunday, September 27th, 2026
- Graduate Program Event
- GMaWiP Welcome Brunch
- Time: 11:00 am - 1:00 pm
- Place: Aubergine on Williamson St
- Abstract: Annual welcome potluck brunch! All career stages welcome: undergrads, postbaccs, grads, postdocs, faculty, staff. RSVP (and optionally sign up to bring something).
Send questions to Amii Matamoros Delgado <matamorosdel@wisc.edu> - Host: GMaWiP
