Colloquia

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Do you want to have a career in physics?  Do you want to help others find a career in physics?  Do you want to be a better mentee or mentor?  If you answered “yes” to one of those questions, this presentation is for you! Physics degree holders are highly employable in both the private and public sectors. However, students, early career scientists, and even senior faculty are often unaware of the available career paths. This talk will provide data on the number of physics degree holders and where they typically find employment, give examples of common career paths, and highlight career resources useful for exploring options and searching for and applying for jobs. The importance of mentorship along the career trajectory will be highlighted.  Tips will also be provided on finding mentors and serving as a mentor.  The speaker will also discuss his career and mentee/mentorship path.  Undergraduates are encouraged to attend.  

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Over the last few decades physicists have delved deeply into student learning and applied this understanding to create curricula and environments that dramatically improve student outcomes that: increase student mastery of the subject, broaden who participates in and succeeds in physics, and advance pathways to success for our major.  More recently, we have built on these successes of knowing what to do by developing novel tools, technologies, and models for how we might create sustainable and scalable approaches. In this talk, I discuss examples of educational innovations that have dramatic impacts, the promises and pitfalls of new technologies (including generative artificial intelligence), and how we, at the departmental scale, might systematically build these improvements into our programs. 

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Black holes are utterly simple to describe---regions of space from which nothing can escape---but nevertheless have profound implications across widely disparate fields of physics.  The study of quantum effects near black holes challenges our most basic notions of quantum information, while observational astronomy demands black holes as an energizing power source for a huge variety of spectacular displays.  After reviewing the history of the black hole idea and describing their role in modern astronomy and quantum gravity, I will turn to two recent developments in the two fields.  On the astronomy side, I will discuss black hole imaging and a proposed space mission, the Black Hole Explorer, that will measure light that has orbited the black hole before arriving at the detector.  On the fundamental physics side, I will discuss the recent discovery that black holes decohere all quantum superpositions, even those held far outside the horizon.  These topics are united by the remarkable conceptual depth that emerges from the simple underlying description of a black hole.

Electron scattering has been a tool of choice for the precision study of nucleon and nuclear structure since the pioneering, Nobel Prize-winning investigations by Robert Hofstadter and collaborators at Stanford during the 1950s. Over the ensuing decades, as accelerator capabilities increased, such experiments generated a wealth of knowledge of the rich and complicated structure of nucleons and nuclei, answering many questions and raising many more. Owing largely to the understanding gained from electron scattering, nucleons are now understood to consist of elementary quarks and gluons confined by strong interactions, described within the Standard Model by Quantum Chromodynamics (QCD). The Continuous Electron Beam Accelerator Facility at Jefferson Lab (JLab), with its medium energy, its unrivaled intensity, duty cycle and polarization performance, and its four experimental halls with complementary target and detector capabilities, is uniquely suited to the investigation of strong interaction physics at the luminosity frontier. Among the most famous results in the history of JLab is the surprising discovery of the rapid decrease with four-momentum-transfer Q2 of the proton’s electromagnetic form factor ratio G p E /Gp M using the polarization transfer method. These measurements upended long-held notions about the proton’s internal structure, revealed the importance of quark orbital angular momentum in understanding the origins of the proton’s spin, and exposed the limits of applicability of the one-photon-exchange approximation in the interpretation of electron scattering data. The technical challenges involved in extending the Q2 reach and precision of these measurements motivated the development of medium-acceptance, open-geometry spectrometers capable of precision charged-particle tracking in an environment of extremely high luminosity and background rate. The detector capabilities required to measure the proton form factor ratio at very large Q2 enable a large, ambitious physics program including high-Q2 proton and neutron form factor measurements, single-spin asymmetries in semi-inclusive deep inelastic scattering, measurements of the pion structure function using tagged deep inelastic scattering, and more. The collection of apparatus developed to carry out this ambitious program is collectively referred to as the Super BigBite Spectrometer (SBS). After 14 years of development, the SBS program started in JLab’s Hall A in 2021. Three major experiments measuring neutron form factors at large Q2 have already been completed, while the “flagship” measurement of G p E /Gp M is scheduled to run in 2025. In this colloquium, I will give an overview of the SBS apparatus, science program, and technical achievements, the data analysis status of completed experiments, and the outlook for completing the remaining approved physics program. Time permitting, I will also discuss some potential future opportunities taking advantage of the unique capabilities of SBS.

The SpinQuest experiment (Fermilab E1039) is designed to explore one of the fundamental questions in hadronic physics: the contribution of sea quarks to the nucleon’s spin. Utilizing a 120 GeV unpolarized proton beam directed at a polarized proton and deuteron target, SpinQuest aims to measure the Sivers function, which describes the correlation between the momentum direction of the struck quark and the spin of its parent nucleon. By focusing on both Drell-Yan and J/ψ production processes, SpinQuest seeks to provide critical insights into the spin and momentum structure of the nucleon, particularly the contribution of antiquarks to its overall spin. I will present the motivation behind the experiment, including the importance of the Sivers function and how SpinQuest can advance our understanding of spin-dependent phenomena in QCD. I will also discuss the experimental design and progress, highlighting recent milestones such as the successful commissioning of the polarized target system and the initial polarized data collection.  I will review ongoing analysis and the roadmap toward extracting the Sivers asymmetry. Additionally, I will outline the experimental challenges faced, future plans for data collection, and the expected contributions of SpinQuest to the global understanding of nucleon structure.

Despite its unparalleled successes, the Standard Model (SM) of elementary particles and their interactions is known to be incomplete. Additional particles and phenomena must exist. I will report on a few precision experiments which my group participated in. Their common goal is to search for physics beyond the Standard Model (SM). The Nab experiment just started to take neutron beta decay data, with goals to (a) confirm or refute current evidence for the violation of unitarity of the quark mixing matrix, and (b) to search for scalar and tensor interactions. The whispering gallery experiment is investigating quantum states of neutrons in close vicinity of a curved mirror that are sensitive to new short-range interactions in the range of nanometers which could be mediated by light scalar or pseudoscalar bosons. The MUonE experiment investigates the apparent failure of the SM to correctly predict the magnetic moment of the muon by observing the running of the fine structure constant in muon-electron scattering.

The Higgs Boson discovery in 2012 required us to think differently about planning for the future of Particle Physics twice now, since that summer 12 years ago. While the decades-long confirmation of the Standard Model itself is a historic episode – as a guide to the future,  it’s not as helpful as one would like because the Standard Model is complete! I will describe Particle Physics planning in the US, review the features of the Standard Model that make it superb, point out why it’s frustrating, and describe hints that continue to motivate us for the coming decades.

Gravitational waves are distortions in the fabric of space and time that are a feature of general relativity, and which were detected one-hundred years after their prediction. The Advanced LIGO and Virgo detectors have observed gravitational waves from nearly one-hundred collisions of black holes and neutron stars, and they are detecting a comparable number during their ongoing observing run. In this talk, I will review the status of these gravitational-wave detections and discuss their implications for understanding fundamental physics through two examples. The first case pertains to the gravitational-wave memory effect: a lasting change in the gravitational-wave strain that is closely connected to the infrared properties of gravitational scattering. LIGO and Virgo will be able to make a statistical measurement of the memory effect towards the end of this decade. I will also discuss new generalizations of the memory effect and their gravitational-wave signatures. The second case relates to using gravitational waves to study dark matter. When a stellar-mass black hole inspirals into a massive black hole surrounded by a high dark-matter density, the dark matter will influence the inspiral of lighter black hole and the gravitational waves emitted from such a binary. I will show how the planned space-based gravitational-wave detector LISA can detect these gravitational waves and measure the presence of dark matter in these binaries.

This year marks two decades since the theoretical discovery of the quantum spin Hall effect. It is exhibited in two-dimensional insulators with a topologically non-trivial band structure, which leads to the existence of helical edge states. The theoretical proposals were soon followed by an experimental discovery of the quantum spin Hall effect in HgTe/CdTe heterostructures. Since then, thousands of papers have been written on the subject, yet very few (perhaps only two) relevant materials have been discovered, and very few theoretical works have claimed to quantitatively explain experimental data. One such material, now established to exhibit the quantum spin Hall effect, is the monolayer tungsten ditelluride. In addition to the quantum spin Hall state, it hosts a correlated insulator ground state at low doping, as well as superconductivity at high enough electronic density. This material will be the main focus of the talk.

After a brief of the research pursued in my group, I will describe our efforts to explain experimentally observed singular linear and nonlinear magnetotransport on the helical edge of the monolayer tungsten ditelluride. I will discuss a model of bulk midgap states "side-coupled" to the edge which appears to account for many experimental features, particularly the dependence of various transport coefficients on the direction of the external magnetic field, as well as their singular dependence on its magnitude.

The pyramids of ancient Egypt and of pre-Hispanic Mesoamerica have fascinated people since the cultures that built them vanished into the annals of history.  How were they built?  What were they used for?  Are there unknown internal substructures, perhaps hidden chambers that have yet to be discovered?  Using the detector technology we developed for a particle physics experiment at Fermilab, we intend to perform non-invasive searches for hidden structures at the Great Pyramid of Khufu, in Egypt, and at the Temple of Kukulkán at Chichén Itzá.  The apparatus will detect cosmic-ray muons produced high in the atmosphere that course through the pyramids to produce a tomographic image of their interiors. I will review the status of both projects, describe in detail the technique we intend to use, present recent simulation results and detector prototype results.

Inspired by the work of Hermann von Helmholtz, William Thomson proposed in 1867 that atoms could be vortices in the aether. While subsequent experiments put this proposal out of business, the concept of topological solitons as fundamental building blocks or artificial atoms remains enticing. Recent developments since the 1960s have revealed ample evidence that nature offers updated versions of the aether concept. In the realm of quantum magnets, the aether manifests as the vector field of magnetic moments, whose topological solitons can be seen as emergent mesoscale atoms. Analogous to real atoms, these solitons organize into periodic arrays or crystals governed by principles of symmetry, anisotropy, and competing microscopic interactions. These magnetic textures generate an effective magnetic field, coupled to the orbital degrees of freedom of conduction electrons, capable of reaching astronomical magnitudes. We will explore how these topological magnetic structures manifest in real materials and how the quantum mechanical nature of spins can give rise to more intricate skyrmion textures than those observed thus far.

The quantum laws governing atoms and other tiny objects seem to defy common sense, and information encoded in quantum systems has weird properties that baffle our feeble human minds. John Preskill will explain why he loves quantum entanglement, the elusive feature making quantum information fundamentally different from information in the macroscopic world. By exploiting quantum entanglement, quantum computers should be able to solve otherwise intractable problems, with far-reaching applications to cryptology, materials, and fundamental physical science. Preskill is less weird than a quantum computer, and easier to understand.

In 1964, when Thorne was a student, there were hints that our universe might have a Warped Side:  Objects and phenomena made from warped space and warped time instead of from matter.  Thorne and his colleagues have spent these past sixty years turning those hints into clear understanding.  They have explored the Warped Side through theory (using mathematics and computer simulations to probe what the laws of physics predict) and through astronomical observations (primarily with gravitational waves). In this lecture he will describe what they have learned about Warped-Side phenomena:  black holes, wormholes, gravitational waves, our universe’s big-bang birth, and the possibility of time travel.

The particle nature of dark matter is an outstanding mystery at the intersection of particle physics and cosmology.  The axion, originally proposed to explain a purely particle physics problem, is one of the most compelling candidates for dark matter.  In the last decade, the field of axion searches has undergone a renaissance of new ideas and improvements to experimental sensitivities.  I will give a brief overview of the field of dark matter axion searches and a more detailed look into the leading axion dark matter search, ADMX.

We report on a precise measurement of the electron-antineutrino angular correlation (the “a” coefficient) in free neutron beta-decay. The “a” coefficient is inferred from the recoil energy spectrum of the protons which are detected in the aSPECT spectrometer. The measurement is substantially more precise than what has been achieved previously, and its implications will be discussed. An alternative analysis is presented that allows for Beyond Standard Model Physics, specifically a non-zero value for the Fierz term “b”. The result constitutes the most precise determination of “b” in free neutron beta decay, and is consistent with the Standard Model prediction. In the Standard Model, however, the aSPECT result for “a” is inconsistent by about 3 sigma with the value for the beta asymmetry “A” recommended by the Particle Data Group. A combined analysis of the results from PERKEO III, which dominates the beta asymmetry average, and aSPECT, now allowing for a non-zero Fierz term, reconciles the two. It finds a more precise value for the Fierz term, consistent with the one obtained from aSPECT data alone, but about 3 sigma away from the Standard Model value, and suggests scalar and tensor interactions in free neutron beta decay.

Olivia Mostow:  The Core-Cusp Problem in Low-Mass Galaxies: Is One Burst Enough? (15 minutes)

We present a novel method for assessing the ability of a single burst of star formation to transform dark matter cusps into cores in low-mass galaxies. Following the approach of Rose et al. 2022, we manually add a contribution to the potential that accounts for a centrally concentrated baryon component within an otherwise dark matter only simulation. This approach allows us to maintain control over how and when these bursts occur. We demonstrate that this method can reproduce the established result of core formation for systems that undergo multiple episodes of bursty outflows. In contrast, we find that equivalent models that undergo only a single (or small number) of burst episodes do not form cores with the same efficacy. This is important because many low-mass galaxies in the local universe are observed to have tightly constrained star formation histories that are best described by a single, early burst of star formation. Using a suite of cosmological, zoom-in simulations, we identify the regimes in which single bursts can and cannot form a cored density profile, and therefore, can or cannot resolve the core-cusp problem.

Sam Crowe:  Unveiling Massive Star Formation: Near-Infrared Observations of Protostellar Jets (15 Minutes)

Massive stars are significant throughout the universe, as they impact their surroundings from the early stages of their formation until they die in the form of supernova. Observations in the near-infrared (NIR) of the bright and large-scale (~parsec) jets that young stars ubiquitously produce during their formation process can place important constraints on the phenomenon of massive star formation. Here, I present a detailed NIR view of two massive star-forming complexes at opposite ends of the sky, AFGL 5180 and Sagittarius C, utilizing extremely high-resolution imaging from the Large Binocular Telescope, Hubble Space Telescope, and James Webb Space Telescope. In AFGL 5180, the data reveal several multidirectional outflows indicative of highly clustered star formation, confirmed by the detection of over a dozen compact sub-millimeter sources using data from the Atacama Large Millimeter/Submillimeter Array (ALMA). By sampling the number density of young stellar objects in the vicinity of the central massive (~12 Msun) protostar, and comparing with recent numerical simulations, we present a novel method for directly distinguishing between theories of massive star formation in situ. Conversely, in Sagittarius C, located in the turbulent and chaotic center of our Milky Way, we find relatively ordered and isolated massive star formation, evidenced by collimated and undisturbed NIR jets. We report the discovery of a new star-forming region ~1 arcminute to the west of Sagittarius C, hosting two prominent bow shocks visible in the NIR imaging, and characterize the most luminous protostar in each neighboring complex via ancillary ALMA data and Spectral Energy Distribution fitting, shedding light on how the process of massive star formation is unfolding in this extreme region.

Alex Rosenthal:  Mass-Loss Rates for Massive Stars from Stellar Bowshocks (15 Minutes)

Massive stars lose a significant portion of their mass through stellar winds over the course of their lifetime, and understanding the rate of mass-loss is critical for understanding stellar evolution and compact object genesis. Traditional methods of determining mass-loss rates rely on UV observations and parameterizing a “clumping” factor, which varies significantly and results in a two-order-of-magnitude difference between prediction and observation for stars with weak winds. We intend to address this “weak-wind problem” using a novel method to measure mass-loss rates of massive stars powering stellar bowshocks using optical spectroscopy of the central stars, far infrared measurements of the bowshock nebulae, and space velocities calculated from GAIA DR3 proper motions. This method utilizes the geometry of the bowshock and the principle of balancing the momentum flux between stellar winds and ambient interstellar material to make a mass-loss rate determination. We observed late-O and early-B type stars with bowshocks with the Apache Point Observatory 3.5m telescope with the KOSMOS long-slit spectrograph and the Wyoming Infrared Observatory’s 2.3m telescope with an optical spectrograph. We used the emcee package in Python and interpolated between models from the PoWR OB-I grid to fit their spectra to find temperatures and surface gravities. We found that our sample spanned a range of stellar parameters, with temperatures varying from 16,000-38,000 K and the log of surface gravity ranging from 2.8-4.1 dex. Using these parameters and photometric data, we calculated predicted mass-loss rates. This work is supported by the National Science Foundation under REU grant AST 1852289

The Electron-Ion Collider (EIC) is a pioneering new particle accelerator that will be built on the current site of the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. It will provide high energy collisions of polarized electrons with polarized protons and ions, allowing for experiments that probe the nature of strong interactions to unprecedented precision. The EIC Project has grown and evolved rapidly since the official launch by the U.S. Department of Energy in 2020. This talk will discuss the primary physics themes driving the EIC effort, the recent milestones achieved by the project and the efforts to establish two complementary detectors at adjacent interaction regions. 

We utilize transport systems daily to commute, e.g. via road networks, or bring energy to our houses through the power grid. Our body needs transport networks, such as the lymphatic, arterial or venous system, to distribute nutrients and remove waste. If the transported quantity is information, for example carried by an electrical signal, then even the internet and the brain can be thought of as members of this broad class of webs. Despite our daily exposure to transport networks, their function and physics can still surprise us. This is exemplified by the Braess paradox, where the addition of an extra road in a network worsens rather than improves traffic contrary to a naïve prediction.

In this talk we will explore two cases that highlight the importance of time in load transmission in transport networks. In the first problem, we will discuss how short timescale dynamics in the flow alters the topology of the network in longer timescales, and shapes its morphology. We will first present the system of phenomenological adaptation equations that govern the structural evolution of vascular networks. We will then demonstrate how implicit of explicit dynamics in the boundary conditions (the power supply, or heart) can drastically alter the network topology, and discuss the implications for the development and function of human circulation. Moving to a larger system, will provide evidence that the similar dynamical developmental rules to the ones that are thought to control vascular remodeling in humans also shape tidal delta geomorphology. 

In the second problem, we consider stochastic transport in geometrically embedded graphs. Intuition suggests that providing a shortcut between a pair of nodes improves the time it takes to randomly explore the entire graph. Counterintuitively, we find a Braess' paradox analog. For regular diffusion, shortcuts can worsen the overall search efficiency of the network, although they bridge topologically distant nodes. We propose an optimization scheme under which each edge adapts its conductivity to minimize the graph's search time. The optimization reveals a relationship between the structure and diffusion exponent and a crossover from dense to sparse graphs as the exponent increases.