Colloquia / Seminars
The UNC Physics colloquium takes place 3:30-4:30pm ET in Phillips 207 unless otherwise stated.
Campus Life Experience (CLE): Throughout their academic career, a student will need to complete 16 CLEs as part of the requirements for graduation. CLE events in Heel Life will count for a student. Students should attend at least 2 CLE events per semester. Attendance at
colloquiums will qualify as CLE credit.
Fall 2024
M, Sept 16
Towards the three-hadron S matrix from QCD
Andrew Jakura, College of William and Mary
Accessing the hadron spectrum from Quantum ChromoDynamics (QCD) poses several challenges given its non-perturbative nature and the fact that most states couple to multi-particle decay modes. Although challenging, advances in both theoretical and numerical techniques have allowed us to determine few-body systems directly from QCD. A synergistic approach between lattice QCD and scattering theory offers a systematic pathway to numerically compute properties such as the hadron spectrum from first principles. I will present an overview of this program and discuss developments in determining three-hadron scattering processes using lattice QCD. These techniques allow us to push the boundaries of resolving the few-body problem in spectroscopy from first-principles.
M, Oct 14
From dust to dust: Using infrared surveys to reveal the explosive life cycles of stars and their remnants
Kishalay De, MIT
Multiplicity is ubiquitous in stars and the remnants they leave behind. While eruptive mass transfer has profound impacts on their long term evolution, the resulting processes are commonly enshrouded in dust produced by mass outflows, preventing direct observational constraints at optical/X-ray/UV bands. In pursuit of a complete census of the role of accretion outbursts in stellar and black hole evolution, I will present the WISE Transients Project — a new effort aimed at a complete census of the variable mid-infrared sky using 15 years of data from the NEOWISE survey. With systematic selection from millions of new infrared variables, I will highlight recent and ongoing work revealing i) a missed population of dusty stellar mergers in our Galactic backyard, ii) new insights into the fiery fates of close planetary worlds, iii) the birth of black holes from dusty eruptions of stripped stars and iv) eruptive pre-supernova mass loss revealed in the dusty aftermath of nearby supernovae. I will end with an overview of the exciting upcoming decade of ground-based infrared surveys that is poised to finally reveal a complete roadmap from stellar birth to the stellar graveyard.
M, Oct 21
Title: Identifying the Origin of Exoplanetary Diversity
Joey Rodriguez, Michigan State
Abstract: Nearly thirty years after the Nobel-prize-winning discovery of the exoplanet 51 Pegasi b, astronomers have discovered thousands of planets outside the solar system, and the field of exoplanetary astronomy has shifted from purely being driven by discovery to performing demographic analysis, and detailed characterization of properties like mass, radius, and atmospheric composition. However, even today, basic questions remain, like “why do some systems end up looking like the Solar System with orderly co-planar architectures, with small planets close-in, and giant planets orbiting far from their stars, while others, like the so-called Hot Jupiters, are dramatically different?” My team and I are tackling this question from both sides: understanding the evolutionary origins of hot Jupiters and understanding the properties of compact multi-planet systems. Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and Kepler/K2 missions, we are working to find keystone planetary systems around bright stars (those well suited for atmospheric observations) that can help address specific questions about planet formation and evolution. I will review our efforts to discover and characterize hundreds of hot Jupiters while investigating the compact architectures of small rocky planets. Finally, uncertainty in planetary orbital solutions for hundreds of planets have accumulated since their initial detection to the extent that they are not accessible with the James Webb Space Telescope (JWST) to study their atmospheres. I will also discuss how we are addressing this problem on a large scale to make hundreds of planets accessible for JWST.
M, Nov. 4
Quantum Computation for Quantum Chromodynamics
Paulo Bedaque, University of Maryland
The first major application of quantum computing may very well be in the realm of quantum physics itself, with a particular focus on problems involving the strong nuclear force, which are prime candidates for the use of quantum computation. As we anticipate the advent of large-scale, error-corrected quantum computers, there are key conceptual challenges that must be addressed. This includes a fresh approach to Quantum Field Theory simulations. In this colloquium, we will explore some of the ongoing efforts and ideas in this quest.
M, Nov. 11
Modern CT Theory: Insight and Beyond
Ge Wang, Rensselaer Polytechnic Institute
Over the past century, computed tomography (CT) has experienced rapid advancements, grounded in integral geometry, linear algebra, and numerical optimization, each marked by sophisticated mathematical nuances. Today, CT is the most widely used medical imaging modality, with approximately 300 million scans performed annually worldwide for screening, diagnosis, and therapeutic guidance across a broad spectrum of diseases. In this talk, I will provide a heuristic overview of CT theory, spanning from classical Fourier slice theorems to modern algorithms for cone-beam spiral CT image reconstruction. Then, I will delve into cutting-edge topics such as interior tomography, robot-based CT, and stationary CT, with an emphasis on generative AI-based image reconstruction.
M, Nov. 18
Spectrum Management at the National Radio Astronomy Observatory: Protecting the Spectrum for Radio Frequency Observations
Chris De Pree, National Radio Astronomy Observatory
The National Radio Astronomy Observatory (NRAO) was founded in 1956, and the National Radio Quiet Zone (NRQZ) was established just two years later. In the past 70 years, the NRAO has designed, built and dedicated many of the world’s preeminent radio telescopes, including the 140 Foot Telescope (Green Bank; 1965), the Jansky Very Large Array (VLA; 1980), the Very Long Baseline Array (VLBA; 1993), the Green Bank Telescope (GBT; 2000), and the Atacama Large Millimeter Array (ALMS; 2013). These telescopes have been involved in many groundbreaking astronomical discoveries, most recently the imaging of the event horizons around the black holes at the center of M87 and our own Milky Way. All of these were designed to operate at remote sites, far from sources of radio frequency interference (RFI) that were common at the time that they were dedicated. The modern era has brought with it an explosion in the number of devices that emit radio waves, from kitchen appliances to consumer devices to electronics in the cars that we drive. Even these sources of RFI are potentially manageable at remote sites. Satellite constellations in Low Earth Orbit (LEO) have changed the balance significantly. Satellites like those in the Starlink network mean that even the most remote radio astronomy sites now have a large number of radio transmitters about them at all times. I will describe current NRAO efforts to better understand and alleviate these new challenges to radio astronomy observations.
M, Nov. 25
Particle Physics in Space
Jessie Shelton, University of Illinois Urbana-Champaign
Abstract: The Standard Model of particle physics is a stunning success: it is a rich edifice that can explain the results of just about every terrestrial experiment performed to date. But this success is “stunning” also in the sense that the Standard Model still leaves many mysteries unexplained. Chief among these mysteries is the ample extra-terrestrial evidence that the Standard Model is missing several important pieces: the physics responsible for dark matter, for preferring matter over antimatter, and for generating the primordial fluctuations that ultimately grew into the galaxies we see today. In this talk I will discuss how we can use the cosmos as a window onto the particle physics of our universe, and how astrophysical and cosmological observations can be used to help us understand the shapes of the pieces missing from the Standard Model. In particular I will talk about scenarios where we can connect particle physics interactions to the mass scales of early proto-galaxies, which can leave subtle gravitational footprints in our observable universe today.
M, Dec. 2
Tidal Disruption Events: Hungry Black Holes and Astrophysical Probes of Fundamental Physics
Nick Stone, University of Wisconsin
Abstract: The centers of most galaxies contain supermassive black holes (SMBHs), enormous objects that contain between a million up to ten billion times the mass of our own Sun. Despite the centrality of SMBHs to many areas of astrophysics, little is known about their origins, largely due to the difficulty inherent in studying them. Occasionally, however, a dormant SMBH can be illuminated by the death throes of a passing star, ripped apart by the tidal field of the SMBH itself. These tidal disruption events (TDEs) result in powerful, multiwavelength flares that outshine the combined luminosity of all the stars in the host galaxy combined for a period of months. TDEs have unique potential for studying SMBHs, in particular for measuring their masses and spins, but this potential has remained so far unfulfilled due to the complex, nonlinear hydrodynamics of the disruption’s aftermath. I will discuss recent first principles radiation-hydrodynamics simulations that for the first time have allowed us to model a realistic TDE, using novel moving-mesh algorithms. I will also discuss the application of more idealized models to TDE emission, and show how their use can turn TDEs into powerful tests of fundamental physics, from the existence of ultralight bosons to the validity of the cosmic censorship conjecture.
Spring 2025
M, Jan. 13
Computational material property and discovery from density functional theory and machine learning
Mengen Wang, The State University of New York at Binghamton
Abstract: First-principles density functional theory (DFT) calculations have contributed to assessing material properties and revolutionized materials science and condensed matter physics. Examples of material properties include mechanical properties, electrical and thermal conductivity, catalytical properties, and optical properties. The predictive power of first-principles calculations in assessing material properties provides opportunities for high-throughput calculations and accelerated screening of new materials, which help the experimental search of chemical spaces and synthesizing conditions.
Defects and surfaces are ubiquitous in materials and can alter their functionalities. Functional defects can be shallow donors or acceptors contributing to the n-type or p-type conductivity of semiconductors. Surface and grain boundary properties are relevant to material degradation mechanisms and defect incorporation. Using halide perovskite as an example, I will present how we use DFT calculations combined with machine learning to understand the defect and surface properties of semiconductor materials. In the first part of my talk, I will introduce the DFT computation of defect formation energy and charge transition levels of dopants in a perovskite material CsSnI3 and the training and prediction of machine learning regression models. In the second part of my talk, I will introduce how machine learning interatomic potentials are trained and applied to constructing surface phase diagrams of perovskite materials, including CsSnI3 and CsPbI3. To conclude, I will discuss the remaining challenges and outlooks in computational defects and surface studies combining high-throughput DFT calculations with machine learning methods.
W, Jan. 22
Science-informed AI for learning materials physics
Ayana Ghosh, Oak Ridge National Laboratory
Abstract: In recent years, artificial intelligence (AI) and machine learning (ML) methods have been rapidly adapted in the physical sciences to gain a comprehensive understanding of material structures, properties, evolution of systems over spatial-temporal resolution, and processes involving phase transitions across various time- and length-scales. Numerous studies exist that encode complex graphs, symbolic representations, invariances, and positional embeddings in these models for targeted design. However, the inherent correlative nature of ML models does not capture the causal, hypothesis-driven nature of the physical sciences. This presentation will focus on a few instances to demonstrate how causal ML models and hypotheses-driven active learning approaches can be exploited in combination with materials representation to extract fundamental atomistic mechanisms that are directly tied to experimental observables, especially for functional materials in the domain of perovskites and two-dimensional systems.
M, Jan. 27
New physics in symmetry-breaking antiferromagnets
Linding Yuan, Northwestern University
Abstract: Central to the study of spin-related phenomena is the capability to create spin polarized states. The conventional way of creating spin polarization entails the involvement of net magnetization or spin-orbit coupling (SOC). The latter entails heavy elements that lead to weak bonds and undesirable defects. The recent discovery of unconventional momentum-dependent non-relativistic spin splitting (NRSS) in certain symmetry-breaking antiferromagnets provides an alternative method for achieving the goal that holds promise for antiferromagnetic spintronics. This phenomenon, envisioned by Pekar and Rashba in 1964, arises from the intrinsic microscopic magnetic fields of these materials. Despite having zero net magnetization, NRSS AFMs exhibit split energy bands with opposite spin polarization—a characteristic feature of ferromagnets (FMs). This resemblance to FMs endows them with a multitude of exotic physical properties. Due to these unique characteristics, a new term, “altermagnet” has recently been coined to describe this special class of antiferromagnets. In this colloquium, I will be highlighting my journey in the process of the discovery of new physics and materials, the people I have been interacting with, and the lessons I have learned along the way.
W, Jan. 29
Insight into the Quantum Materials
Ling-Fang Lin, University of Tennessee-Knoxville
Abstract: Due to the interplay between spin, charge, orbital, and lattice degrees of freedom, many interesting phenomena emerged in quantum materials, such as superconductivity, magnetism, orbital ordering, etc. Recently, the newly discovered Ruddlesden–Popper nickelate bilayer La3Ni2O7 and trilayer La4Ni3O10 superconductors, have unveiled a new and exciting platform for exploring high-Tc superconductivity, where the Ni orbital degree of freedom plays a key role, different from the previously studied infinite layer nickelates and cuprates. In this talk, I will provide our insightful microscopic view of these novel phenomena. In addition, ferromagnetic insulators are valuable for their potential in spintronics applications due to their unique property of exhibiting magnetic behavior while remaining electrically insulating. In this talk, I will introduce a new mechanism for obtaining ferromagnetic insulating phase.
M, Feb. 3
Title: Ab Initio Many-Body Physics in Light-Driven Quantum Materials
Zhenbang Dai, University of Texas-Austin
Abstract: Light-matter interaction is of particular importance in quantum systems, which is central to technological applications such as optoelectronics, spin-current generation, and artificial photosynthesis. It is also rooted in many fundamental physical processes, including creating and manipulating emergent quasiparticles, engineering topological phases, and cavity electrodynamics, enabling a plethora of experimental spectroscopies for the detection of exotic phases and behaviors under extreme conditions. The lattice vibrations in quantum materials, and the incurred electron-phonon coupling, are among those factors that make the manifestations of light-matter interaction so versatile, and in this talk, I will discuss two consequences of light-matter interaction in systems with vibrational degrees of freedom, from the perspective of ab initio many-body perturbation theory. First, I will focus on continuous light illumination and discuss our recent understanding of the DC photocurrent generation in homogeneous materials without traditional p-n junctions, whose origins entangle quantum geometry and many-body electron-phonon interaction. The second consequence concerns the fate of light-induced excitons after turning off the illumination. By developing an ab initio theory for the correlated electronic system dressed by phonons, I will illustrate how excitons get trapped by themselves via excited-state dynamical relaxation, showing that the optical properties of quantum materials could be drastically changed due to these self-trapped excitons.
M, Feb. 17
Title: High-Redshift Galaxies and Quasars
Mike Shull, University of Colorado-Boulder
Abstract: This talk will present an overview of astronomical techniques for discovering and characterizing high-redshift galaxies and quasars with Hubble Space Telescope and the James Webb Space Telescope. After describing recent highlights on galaxies and quasars at redshifts (z > 8), I will discuss the implications and applications to reionization of the intergalactic medium (IGM), feedback from stars and quasars, and models for how galaxies form and grow in the first Gyr of the universe.
M, Feb. 24
The Exploration of the Pluto System and the Kuiper Belt
Alan Stern, Southwest Research Institute
Abstract: New Horizons is NASA’s mission to explore Pluto, its system of satellites, and the Kuiper Belt. The $1B New Frontiers mission launched in 2006 and, following a 2007 Jupiter Gravity Assist flyby made the first spacecraft reconnaissance of the Pluto system in 2015 and the first exploration of a Kuiper Belt Object in 2019. The mission continues to explore the Kuiper Belt and also the Sun’s outer heliosphere, and has made a number of wholly unique, groundbreaking astrophysical observations. n this talk I will describe the mission, its major scientific results, and its plans and prospects going forward.
M, Mar. 3
Evaluating and supporting lab group work
Natasha Homes, Cornell University
Abstract: While group work is common in most lab courses, research has raised concerns about students’ experiences in those groups. This talk will explore work evaluating how students participate in the hands-on aspects of labs, particularly illuminating imbalances between men’s and women’s participation, the effect of instructional interventions on that participation, nuances in students’ perceptions of these experiences. I’ll also discuss open research questions for supporting lab group work and present preliminary work towards measuring participation at scale.
M, Mar. 17
Title forthcoming
Antonella Palmese, Carnegie Melon
Abstract forthcoming
M, Mar. 24
Title forthcoming
Todd Henry, Georgia State
Abstract forthcoming
M, Mar. 31
Title forthcoming
Brooke Russell, MIT
Abstract forthcoming
M, Apr. 7
Title forthcoming
Laura Greene, National High Magnetic Field Laboratory
Abstract forthcoming
M, Apr. 14
Title forthcoming
Katelin Schutz, McGill
Abstract forthcoming
M, Apr. 21
Title forthcoming
Elisabeth Newton, Dartmouth
Abstract forthcoming
M, Apr. 28
Title The Far Ultraviolet diffuse background
Shri Kulkami, Caltech
Abstract Historically, the search for the inter-galactic medium
(IGM) motivated the search for the Far Ultraviolet (<0.2 micron;
FUV) background which in turn led to a number of experiments and missions. Decades later the focus shifted to FUV as the primary heating and ionizing agent of the atomic phases (warm and cold neutral medium). On the observational side, it was realized that at high Galactic latitudes, the diffuse FUV has three components:
FUV light from hot stars in the Galactic plane reflected by dust grains (diffuse galactic light or DGL), FUV from other galaxies (extra-galactic background light, EBL) and a component of unknown origin. This view has been amply confirmed by later GALEX observations. During the eighties, there was considerable discussion that decaying dark matter particles produced FUV radiation. In my talk I systematically investigate production of FUV photons from all major processes and sites of FUV production: the Galactic Hot Ionized Medium (line emission), two photon emission from the Warm Ionized Medium, fluorescence of molecular hydrogen, low velocity shocks in the Galaxy and Lyman fluorescence in the Solar System (the interplanetary medium and the exosphere of Earth). I will end the talk introducing the Ultraviolet Explorer (UVEX).