Colloquium Calendar

TBD

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.

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, 
and biosignatures.

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.

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. 

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. 

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.

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.

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.

Profile: https://www.bartlowcrustaldef.com/uploads/1/3/3/1/133104821/bartlowcv.pdf

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.

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.