Colloquia - Previous Semesters
January 24, 2022 - Alan Robock - Rutgers University
"Climatic and Humanitarian Impacts of Nuclear War"
A nuclear war between any two nations, such as India and Pakistan, with each country using 50 Hiroshima-sized atom bombs as airbursts on urban areas, could inject 5 Tg of soot from the resulting fires into the stratosphere, so much smoke that the resulting climate change would be unprecedented in recorded human history. Our climate model simulations find that the smoke would absorb sunlight, making it dark, cold, and dry at Earth’s surface and produce global-scale ozone depletion, with enhanced ultraviolet radiation reaching the surface. The changes in temperature, precipitation, and sunlight from the climate model simulations, applied to crop models show that these perturbations would reduce global agricultural production of the major food crops for a decade. Since India and Pakistan now have more nuclear weapons with larger yields, and their cities are larger, even a war between them could produce emissions of 27 or even 47 Tg of soot.
My current research project, being conducted jointly with scientists from the University of Colorado, Columbia University, and the National Center for Atmospheric Research, is examining in detail, with city firestorm and global climate models, various possible scenarios of nuclear war and their impacts on agriculture and the world food supply. Using six crop models we have simulated the global impacts on the major cereals for the 5 Tg case. The impact of the nuclear war simulated here, using much less than 1% of the global nuclear arsenal, could sentence a billion people now living marginal existences to starvation. By year 5, maize and wheat availability would decrease by 13% globally and by more than 20% in 71 countries with a cumulative population of 1.3 billion people. In view of increasing instability in South Asia, this study shows that a regional conflict using <1% of the worldwide nuclear arsenal could have adverse consequences for global food security unmatched in modern history. The greatest nuclear threat still comes from the United States and Russia. Even the reduced arsenals that remain in 2020 due to the New START Treaty threaten the world with nuclear winter. The world as we know it could end any day as a result of an accidental nuclear war between the United States and Russia. With temperatures plunging below freezing, crops would die and massive starvation could kill most of humanity.
As a result of international negotiations pushed by civil society led by the International Campaign to Abolish Nuclear Weapons (ICAN), and referencing our work, the United Nations passed a Treaty to Ban Nuclear Weapons on July 7, 2017. On December 10, 2017, ICAN accepted the Nobel Peace Prize “for its work to draw attention to the catastrophic humanitarian consequences of any use of nuclear weapons and for its ground-breaking efforts to achieve a treaty-based prohibition of such weapons.” Will humanity now pressure the United States and the other eight nuclear nations to sign this treaty? The Physicists Coalition for Nuclear Threat Reduction is working to make that happen.
January 31, 2022 - Natasha Holmes - Cornell University
"The trouble with traditional physics labs"
When you ask physicists to reflect on their intro labs, responses include “boring”, “forgettable”, or “cookbook.” What is so wrong with the traditional lab? An instinctive answer is the structure: students follow procedures without having to think about what’s going on. In this talk, I’ll present work that challenges this instinct and I’ll suggest an alternative answer: namely, that the fundamental goal to use labs to demonstrate phenomena is problematic. I’ll describe several studies that have used quantitative assessments of student learning, analysis of student work, and videos of students conducting lab experiments to shed light on this issue. I’ll also briefly describe how we’ve restructured our introductory lab courses in response to these results.
March 7, 2022 - Tova Holmes (University of Tennessee)
Going the Distance: Searching for Overlooked Physics at the LHC
The LHC has reached a new era: nearly a decade without any large jumps in energy or luminosity. For those interested in finding Beyond the Standard Model (BSM) physics, a paradigm shift is required. In my talk I’ll discuss a search program looking for long-lived particles, which often escape detection from standard BSM searches, due to the difficulty of identifying their unconventional signatures. This results in a long-lived particle landscape full of unexcluded territory, opening up opportunities to find TeV-scale Supersymmetry, hidden sectors, right-handed neutrinos, and more. My talk will explore how and why we should search for these new signatures.
April 4, 2022 - Bjoern Penning (University of Michigan)
Searching for Dark Matter from the Lowest to the Highest Energies
Dark Matter (DM) is a long standing puzzle in fundamental physics and the goal of a diverse research program. In underground experiments such as LZ we search for DM directly using lowest possible energy thresholds, at the LHC we seek to produce dark matter at the very highest energies, and using telescopes we look for telltale signatures in the cosmos. I will present an overview of the status of DM searches using these different approaches and their connection before focusing on the status of the LZ direct Dark Matter experiment. LZ is the world's most sensitive DM experiment and is currently taking data.
April 11, 2022 - Ashley Chontos (University of Hawaii / MIT/ Princeton)
Precise Stellar and Planet Properties in the Kepler, K2 & TESS Era
The Kepler Mission has revolutionized exoplanet science, with over 2000 confirmed planets to date. However, most exoplanet host stars observed by Kepler are too faint to perform extensive radial-velocity follow-up to precisely measure Doppler semi-amplitudes and thus, planet masses. The recent successful launch of the NASA TESS Mission has now opened the door to precisely characterize transiting exoplanets orbiting bright stars in the solar neighborhood. The most promising planets will be those orbiting subgiants, whose rapid phase in stellar evolution provides a unique tool to infer precise stellar ages, masses, radii and densities. Subgiants also provide the opportunity to apply asteroseismology, which is currently the best tool for accurate and precise stellar characterization. In this talk, I will present benchmark Kepler and TESS asteroseismic discoveries, including Kepler’s first new planet host (or KOI-4) and the detection of oscillations in the naked-eye solar-analogue 𝛼 Men A. I will introduce the TESS-Keck Survey (TKS), which is a very large Keck radial velocity survey to confirm and characterize transiting exoplanets discovered by TESS. Finally, I will conclude with early results from an ensemble analysis of TESS planets orbiting subgiant stars as well as its implications for post main-sequence planet evolution.
May 2, 2022 - Kevin Hainline (University of Arizona)
The First Years of JWST: Discovering and Understanding Distant Galaxies
With the successful launch and deployment of JWST, we are only months away from a suite of deep extragalactic surveys that will uncover hundreds of thousands of galaxies well outside of the realm of current observational capabilities. In this talk, I will discuss where we stand in our understanding of the early extragalactic universe and describe how JWST will help us answer longstanding questions about reionization, the evolution of the metal content in the universe, and the role of active galaxies. As a member of the science team for the primary imager on board JWST, JWST/NIRCam, I will discuss the work that we’ve been doing to prepare for the GTO program JADES, the most comprehensive Cycle 1 deep survey which encompasses over 800 hours of combined NIRCam, NIRSpec, and MIRI observations of the well-studied GOODS-S and GOODS-N regions. I will place JADES in context with other planned extragalactic surveys and share the complexities of finding the farthest and faintest galaxies.
May 9, 2022 - Casey De Roo (University of Iowa)
Making and Using X-ray Grating to Study the Local Hot Universe
Exquisite cosmological measurements performed in the last decade provide tight constraints on the amount of baryons – “normal matter” – in the Universe. Yet surveys of our local Universe today come up far short: as much of 50% percent(!) of this normal matter is unaccounted for. Predictions from cosmological simulations suggest a significant fraction of the baryons are at X-ray temperatures and lie undetected in the extended halos of galaxies and clusters. Is there enough material in these reservoirs to get the “right” answer in our local Universe? And what can that material tell us about how it got there?
In my talk, I will discuss prospects for detecting and characterizing this hot gas with future X-ray grating spectrometers. I’ll divide my time between astronomy and instrumentation, giving a brief “state of the field” overview for astronomical X-ray instrumentation, touch on how we are leveraging advances in the semiconductor industry to develop and deploy next-generation X-ray optics, and discuss the advances in the past decade that put this science within reach.
September 20, 2021 - Dawn Williams - Alabama
"The IceCube Neutrino Observatory and the Beginning of Neutrino Astrophysics"
The IceCube Neutrino Observatory is the world’s largest neutrino detector, instrumenting a cubic kilometer of ice at the geographic South Pole. IceCube was designed to detect high-energy astrophysical neutrinos from potential cosmic ray acceleration sites such as active galactic nuclei, gamma ray bursts and supernova remnants. IceCube announced the detection of a diffuse flux of astrophysical neutrinos in 2013, including the highest energy neutrinos ever detected. In September 2018, IceCube observed a neutrino in coincidence with a flaring blazar. I will discuss the latest results from IceCube and discuss prospects for future upgrades and expansions of the detector.
September 27, 2021- Cancelled
October 4, 2021- Pengpeng Zhang - Michigan State
"Phase Transformation and Interfacial Coupling in Heterostructures of Low-Dimensional Materials"
The rapid advances in low-dimensional materials of various crystalline symmetries and elemental compositions have generated rich functionalities. Artificially stacking or stitching dissimilar materials via construction of heterostructures further offers unprecedent potential for tailoring the properties of individual constituents and giving rise to exotic quantum phenomena. In this talk, I will first discuss how we utilize lateral heterostructures to induce phase transition in an inorganic transition metal dichalcogenide core-shell architecture and to unravel the microscopic process of insulator-to-metal transition in a correlated organic charge transfer complex system. I will then discuss the formation of new two-dimensional Sn phases enabled by interfacial coupling on hexagonal boron nitride monolayer on metal (h-BN/metal), which potentially provides a new avenue for engineering electronic and topological properties of 2D Sn.
October 18, 2021- Juliette Becker - Caltech
"Explaining the Orbits of Ultra-Short-Period Planets Through Disk-Planet and Star-Planet Interactions"
Ultra-short-period planets (USPs) reside interior to the expected truncation radius for a typical T Tauri disk, requiring extra explanations for their current orbital locations beyond simple disk migration. In particular, once a planet migrates close to the disk truncation radius, Type I torques will go to zero or switch direction depending on the stellar and disk conditions, and the result is that the planet is expected to stop migration and become trapped. In this presentation, we explain how for suitable disk parameters, magnetically-driven sub-Keplerian gas flow in the inner disk can naturally counteract these effects and subsequently produce USPs at their observed orbital radii. The sub-Keplerian gas flow provides a headwind to small planets, providing a strong torque which can overcome the effects of outwards Type I migration in the inner disk. We also discuss how post-disk dispersal, stellar evolution can lead to a particularly intriguing geometry of system containing ultra-short period planets in high multiplicity systems where the ultra-short period planet and the outer planets exist in two different dynamical states. This has manifested in the observational data as a small number of stars hosting systems of tightly packed coplanar inner planets as well as an ultra-short period planet, where the orbit of the latter is misaligned relative to the mutual plane of the former.
October 25, 2021- Janet Biggs
I am a visual artist whose practice incorporates science and technology. I have collaborated with experts ranging from aerospace engineers to astrophysicists. I will present a number of projects that open innovative ways of seeing and thinking, from the creation of a neurodiverse AI entity to my current collaboration with KU professors Agnieszka Miedlar and Daniel Tapia Takaki (part of the Spencer Museum of Art’s Integrated Arts Research Initiative). Moving between locations, situations, perspectives and disciplines can disrupt existing understandings and open new paths for knowledge building, insight, and communication. Questions are generated by a shift in perspective, a step sideways into an unexpected conversation. Cross-disciplinary collaborations can operate as innovative structures, integrated and substantive to all participant’s respective fields. This talk will introduce methods and models of generative thinking. What new questions can be asked? What new discoveries will be made?
November 1, 2021 - Phil Baringer - KU
"40 Years of the Standard Model"
We'll discuss how the Standard Model of particle physics grew from its uncertain infancy to its formidable adulthood. After some nostalgia about the successes of the theory we'll attempt to take a clear-eyed look at its present status.
November 8, 2021- Feng Wang - Berkeley
“Engineering Correlation and Topology in Two-Dimensional Moire Superlattices”
Van der Waals heterostructures of atomically thin crystals offer an exciting new platform to design novel electronic and optical properties. In this talk, I will describe a general approach to engineer correlated and topological physics using moire superlattice in two dimensional heterostructures. One example is the transition metal dichalcogenide moire superlattices, where a rich set of correlated insulator and generalized Wigner crystal states can be observed. The other example is the ABC trilayer graphene (TLG) and hexagonal boron nitride (hBN) moire superlattice, in which both the bandwidth and the topology of the electronic band can be controlled electrically. It allows us to realize many quantum phases, ranging from Mott insulator and superconductivity to orbital ferromagnetism and Chern insulator, all in a single device through electrostatic gating.
December 6, 2021 - Jorge A. Lopez - Texas El Paso
“Italian delicacies served up in a neutron star crust”
The matter in the outermost layer, or “crust,” of a neutron star (the remnant of a supernova) is believed to host a variety of phases in which dense regions of nucleons are filled with voids of lower density. The presence of the phases, euphemistically referred to as “nuclear pasta” because of their resemblance to the shapes of lasagna, gnocchi, and spaghetti, may affect the emission of neutrinos, the primary mechanism by which the neutron star cools. In this talk, molecular dynamics and a set of topological and geometric descriptors (volume, area, mean curvature, and its Euler characteristic—a number that represents the phase’s topology) are used to accurately identify the pasta phases predicted by dynamical simulations, a labeling scheme that could be used to directly map the shape of a pasta phase to its effect on neutrino emission and neutron star cooling. Ref. https://link.springer.com/article/10.1007%2Fs11467-020-1004-2.
3/2/2020 Professor Timothy Tait, University of California, Irvine - Searching for Particle Dark Matter
3/16/20204 Professor Daniel Tapia Takaki, University of Kansas - Unprecedented photons from the periphery and beyond
3/30/2020 Professor Corey Maley, University of Kansas Department of Philosophy - Analog Computation and Representation
11/4/2019 Professor Anne Medling, University of Toledo - Tracing Black Hole Fueling and Feedback with Adaptive Optics and ALMA
11/11/2019 Professor Javier Duarte (University of California, San Diego) - Deep learning for Higgs and new physics searches at the
11/18/2019 Professor Siyuan Han (University of Kansas) - Superconducting Circuits for Quantum Information Processing
11/25/2019 C.A. Bertulani (Texas A&M University-Commerce) - Neutron Skins, Symmetry Energy, and Neutron Stars
12/2/2019 Anthony R. Timmins (University of Houston) - The structure of the nucleus and proton at the LHC