Talk titles and abstracts can be found in the accordions below the calendar when available. Please visit the department YouTube Channel (external) for recordings of colloquia when available.
Colloquia - Previous Semesters
August 29, 2022 - Stephanie Juneau (NOIR lab)
September 12, 2022 - Daniel Tapia Takaki (KU)
Using the LHC as a photon collider and synergies with the Electron-Ion Collider
In this talk, we will review the science of photon-induced interactions at the CERN Large Hadron Collider. Special emphasis will be put on recent research work and prospects of new experiments led by the PI. Finally, the synergies and new research projects in the context of the Electron-Ion Collider to be built at Brookhaven National Laboratory will also be discussed.
September 19, 2022 - Ian Crossfield (KU), The Final Frontier? The Composition of Rocky Exoplanets and Their Host Stars
The study of exoplanets and their atmospheric compositions is set to
dramatically expand in the coming years with the recent start of JWST
science observations. I will present "JWST precursor" results in two areas
from the KU ExoLab. First, I will report on our successful measurement of the infrared
thermal emission from a terrestrial planet, at 1.2 Earth radii the smallest
planet for which such measurements have been made. Our
measurement begins to constrain surface mineralogy and also reveals
that the planet has essentially no atmosphere for a wide range of
plausible atmospheric compositions, and sets the stage for JWST follow-up.
Second, I will present initial results from our ongoing efforts to measure
precise chemical abundances of exoplanet host stars. Such measurements
are needed because historically measurements of exoplanetary atmospheric
composition have compared only to *solar* abundances (overlooking intrinsic
*stellar* abundances), and are essential in order to permit accurate
interpretation of JWST measurements of exoplanets' atmospheres, surfaces,
October 17, 2022 - Jeyhan Kartaltepe (RIT), The Growth of Galaxy Structure, as Told by Early JWST Imaging
The first images taken with the James Webb Space Telescope (JWST) are unveiling galaxies in the distant universe and enabling detailed studies of their properties. In this talk, I will present some of the first results on how our understanding of the growth of galaxy structure in the universe has changed based on these first images. We have conducted a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z=3-9 using the NIRCam images at 1-5 microns taken as part of the Cosmic Evolution Early Release Science (CEERS) Survey in June 2022. This sample consists of 850 galaxies at z>3 detected in both CANDELS Hubble WFC3 imaging as well as JWST CEERS NIRCam images to enable a comparison of HST and JWST morphologies. Our team conducted a set of visual classifications, with each galaxy in the sample classified by three different individuals. We also measure quantitative parametric and non-parametric morphologies using the publicly available codes Galfit, Galapagos-2/GalfitM, and statmorph across all seven NIRCam filters. Using these measurements, I will present the fraction of galaxies of each morphological types as a function of redshift, compare their morphologies to what we knew based on Hubble imaging, and discuss the implication of these results for galaxy evolution. I will also highlight what we expect to learn from future JWST observations in CEERS, COSMOS-Web, and other Cycle 1 surveys.
October 24, 2022 - Rebecca Levy (U. Arizona), Feeding and Feedback: “Super” Star Clusters in the Center of NGC253
The cycle of star formation governs the evolution of galaxies. At earlier cosmic times, the amount of cold gas and the star formation rate were higher than in the present day. A major open question is whether the process of star formation has also changed over cosmic time. To investigate this question, I present observational results from an archetypal nearby starburst galaxy, NGC253. The star formation rate in the center of this galaxy is much higher than normally star-forming galaxies today and may be more similar to galaxies at earlier cosmic times. First, I will discuss how gas flows to the center of this galaxy along its bar to fuel the extreme burst of star formation. Using very high spatial resolution data from ALMA tracing emission from dust and dense molecular gas, we find that the massive, compact, very young “super” star clusters (SSCs) found in the center of this galaxy are arranged in a ring. Moreover, we find that the SSCs and dense molecular gas are found at the innermost orbit predicted by the barred potential of this galaxy, as expected. Next, I will discuss the detection of massive outflows of molecular gas detected from three of the SSCs. These outflows carry a substantial fraction of the gas mass away from the clusters and may stop these clusters from growing even larger. The precise physical mechanism powering these outflows is uncertain, but winds from massive stars and dust-reprocessed radiation pressure are the best candidates - different from lower mass, less extreme star clusters. Finally, I will discuss the result of this extreme burst of star formation on the galaxy as a whole: the central starburst is driving a galaxy-scale, multiphase superwind. I will show a new detection of the thermal emission from warm dust located on the outermost edge of the superwind. Together, these new observations of NGC253 paint a more complete picture of gas feeding and feedback in an extreme star-forming environment and set the stage for JWST observations coming in Cycle 1.
October 31, 2022 - Neda Hejazi (KU), Cool Dwarfs: Clues on the Chemical History of the Milky Way
Similar to many other galaxies in the Universe, the Milky Way is a highly evolved spiral galaxy. However, despite the advent of large observing programs in the last decade, we are still far from a full understanding of our galaxy’s formation and evolution. Although accounting for large-scale kinematic and dynamic properties of stellar populations is essential in constructing Galactic evolutionary models, the chemical composition of stars holds fundamental clues on how the Galaxy formed and how it has evolved over time. Among different stellar types, low-mass dwarfs, in particular K and M dwarfs, can be used as tools to probe the structure and chemodynamical evolution of the Milky Way. These dwarfs are the most abundant stars in our Galaxy, which constitute a significant part of the Galaxy’s mass in the form of baryonic matter. In addition, due to the slow fusion process in their interiors, the main-sequence lifetime of these cool dwarfs is much longer than the current age of the Universe. As a result, their atmospheric abundances are pristine indicators of the chemical properties of the progenitor molecular clouds where they were born. Moreover, cool dwarfs have increasingly become attractive targets as planet host candidates, because widely used methods in detecting exoplanets such as radial velocity and transit techniques are more sensitive to planets orbiting low-mass stars. The chemical evolution of protoplanetary disks and subsequent planetary formation can be determined by comparing the composition of host stars and their planets. I will underline recent studies of Galactic chemical properties, highlighting approaches to utilize cool dwarfs as tracers of the chemical enrichment history of the Milky Way.
November 7, 2022 - Moiya McTier, The Milky Way: Our Galaxy, a Book, and a Shift in Perspective
Every single human who has ever lived could have called our Milky Way Galaxy "home," but it was only 100 years ago that we learned we live in a galaxy at all. In this talk, Dr. Moiya McTier will highlight the different ways humans have connected to the night sky throughout our history, from myths to telescopes. She will tell you about her process for writing an "autobiography" for the Milky Way, and share how the experience changed the way she interacts with the world. No knowledge of space will be assumed.
November 14, 2022 - David E. Meltzer, Arizona State University, Investigating and addressing physics students’ mathematical difficulties
Throughout the history of physics education, physics students’ mathematical preparation and skills have been a concern both for instructors and educational researchers. The impact of that preparation on students’ success in physics courses has been studied, and many specific mathematical difficulties faced by physics students have been identified. A variety of instructional approaches have been suggested to address these difficulties. I will survey some of the key research findings, and discuss a number of pedagogical strategies that have been employed or are under development.
November 21, 2022 - Noel Bartlow, University of Kansas Department of Geology, The mechanics of megathrust earthquake producing faults illuminated by GPS geodesy
Subduction zones are convergent plate tectonic boundaries which produce the largest earthquakes and tsunamis in the world. These destructive events can cause 10s to 100s of thousands of deaths and billions of dollars in damages. However, in any individual subduction zone these mega disasters occur every 500 to 1000 years, making it difficult to prepare for them. In between the times of large earthquakes subduction zones are not completely quiet, instead they exhibit small motions that can be measured by high precision GPS geodesy. By measuring and modeling these small motions we learn about the behavior of subduction zones, including where future earthquakes might strike and how big they might be. GPS geodesy has also enabled the discovery of so-called slow earthquakes, also called slow slip events, which occur over periods of weeks to years. While not dangerous, these slow slip events have the potential to trigger huge earthquakes and tsunamis and also illuminate the mechanics of friction on subduction zone faults. This talk will introduce GPS geodesy, Prof. Bartlow’s work on slow slip events, and new initiatives in seafloor geodesy with particular focus on a subduction zone in the Pacific Northwest region of the US.
November 28, 2022 - Prof. Tarun Sabarwal (Economics, KU), Control and spread of contagion in networks with global effects
We study proliferation of an action in binary action network coordination games that are generalized to include global effects. This captures important aspects of proliferation of a particular action or narrative in online social networks, providing a basis to understand their impact on societal outcomes. Our model naturally captures complementarities among starting sets, network resilience, and global effects, and highlights interdependence in channels through which contagion spreads. We present new, natural, computationally tractable, and efficient algorithms to define and compute equilibrium objects that facilitate the general study of contagion in networks and prove their theoretical properties. Our algorithms are easy to implement quantifying relationships previously inaccessible due to computational intractability. We conduct millions of Monte Carlo simulations in scale-free networks with 1,000 players, providing quantitative and qualitative insights. The scope of application is enlarged given the many other situations across different fields that may be modeled using this framework.
December 5, 2022 - Prof. Sebastien Lepine (Georgia State University), Dancing with the stars: tracking stellar motions in the vicinity of the Sun to decipher the structure and history of the Milky Way
Thanks to massive astrometric and spectroscopic surveys
we now know the distances, full spatial motions, and chemical abundances
for millions of stars in the vicinity of the Sun. How a star moves
locally depends on its specific orbit around the Galaxy which is
primarily determined by the star's age and point of origin. Stars can
notably be grouped into broad "populations" (disk, old disk, halo)
but a detailed analysis reveals a much more complex dynamical structure,
with stars swarming into "streams" or "moving groups" each with its
own specific origin and history. The kinematics of nearby stars can
thus be used to infer the and evolution of the Milky Way, by using
the stars as "fossils" to retrace the story of its formation and/or
assembly. In this presentation I will first explain how the distances
and motions of so many stars are being and how massive spectroscopic
programs like the Sloan Digital Sky Survey provide critical radial
velocity and abundance measurements, notably for the countless
low-mass stars (K and M dwarfs) which are ubiquitous and long-lived,
but dim and challenging to observe. I will then present results that
showcase the surprising dynamical complexity of our Galaxy, including
evidence for accretion and merger events, spiral arms and orbital
resonances, young moving groups, radial migration, and more.
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