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Events on Thursday, February 9th, 2023

R. G. Herb Condensed Matter Seminar
Constructive approaches to frustrated magnetism: Moiré and Measurements
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Zhu-Xi Luo, Harvard University
Abstract: Frustrated magnetism arises when spins interact through competing exchange interactions which cannot be simultaneously satisfied. When the frustrations are strong enough, exotic states can emerge such as long-range entangled spin liquids. Unfortunately, solid state materials are complicated and frustrations are hard to control: To this date, quantum spin liquids are still challenging to be realized in experiments. Naturally, researchers seek more manageable experimental systems, in the hope of engineering frustrated magnetism constructively. I will discuss my recent works in two types of such manageable systems: moire heterostructures in van der Waals materials where many tuning knobs are available; and monitored quantum circuits where designer gates and measurements are exploited as new sources of frustrations.
Host: Victor Barr
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Hunting EeV Neutrinos with RNO-G and PUEO
Time: 2:30 pm
Place: Chamberlin 4274
Speaker: Cosmin Deaconu, University of Chicago
Abstract: The Radio Neutrino Observatory - Greenland (RNO-G) and the Payload for Ultrahigh Energy Observations (PUEO) are two experiments under construction seeking to detect for the first time the elusive ultrahigh-energy (>~ 100 PeV) neutrinos. Such neutrinos are expected to be produced from interactions of cosmic rays with photons and potentially in astrophysical sources, but detection is challenging due to the low flux. Both experiments operate by attempting to detect the impulsive Askaryan radio emission produced in showers induced by energetic neutrinos interacting in glacial ice. PUEO is a long-duration balloon payload, expected to fly over Antarctica in 2024, while RNO-G uses embedded antennas in Greenland and started deployment in 2021. In this talk, I will discuss the science goals, design considerations and implementation progress of both experiments.
Host: Marjon Moulai
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Astronomy Colloquium
Blue Stragglers, Blue Lurkers and Stars that Go Bump In the Night
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Robert Mathieu, University of Wisconsin - Madison
Abstract: A substantial fraction of evolved late-type stars in the Milky Way have
evolved along alternative stellar evolutionary paths in binary systems, both
in star clusters and in the field. As a case in point, in the 4-Gyr open
cluster M67, 25% of the evolved stars do not lie on the single-star
evolutionary isochrone. Thus, understanding these alternative stellar
evolutionary paths are essential to understanding stellar evolution, and to
correctly interpret ensemble studies of stars in the Milky Way.

Today, blue stragglers are seen as the most evident part of a much larger
population of evolved stars that do not fall on a classical single-star
evolutionary path. Indeed recently this population has suddenly grown
further to include a population of such stars lurking within main sequences.
All of these stars trace major alternative pathways of stellar evolution.
They are not anomalous.

Over the last decade observations have shown that most of these stars are
themselves binary stars. Relatedly, theory has argued that they likely form
from an array of processes within binary stars, including mass transfer,
mergers, collisions, and rapid rotation. I will tell of this discovery
journey through the landscape of rich open clusters.
Host: Ke Zhang
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