PGSS 2025

PGSS Invited Faculty Lecture: Liquid-noble detectors as tools for dark matter and neutrino physics

Scott Haselschwardt

Assistant Professor, Department of Physics

Understanding the particle nature of dark matter is one of the most pressing tasks of modern science, motivating numerous theoretical dark matter candidates and experimental efforts to detect them. Chief among these are direct-detection experiments which use liquified noble gasses as their detection medium. In this talk I will describe direct searches for weak scale dark matter particles, highlighting in particular the LUX ZEPLIN (LZ) experiment, which uses liquid xenon as its detection medium. I will then discuss future efforts aimed at detecting dark matter lighter than the proton, including the development of a low threshold detector based on quasiparticle excitations of a superfluid helium-4 target (HeRALD). Taken together, these experiments directly probe an entire class of extremely well-motivated models known as “thermal relics”: dark matter particles that were once in thermal equilibrium with ordinary matter in the early Universe.

Cancelled (as of 6/5/25)

A Computationalist's P.O.V.: Hierarchical and Dynamical Control of Colloidal Systems

Kate Jensen

Second Year, Department of Physics

Biological materials possess remarkable capabilities unmatched by most synthetic systems, including the ability to dynamically alter their function, shape, or color in response to external stimuli such as temperature, chemical gradients, mechanical forces, or electrical signals. Replicating these adaptive behaviors in engineered materials holds tremendous potential for creating programmable, reconfigurable, and hierarchically structured systems with applications spanning photonics, display technologies, and soft robotics. For the sake of this talk, we will limit our discussion to our ability to mimic four major desirable properties of biological materials that lead to this type of desirable phenomenon: (1) responsiveness to external stimuli, (2) intrinsically hierarchy, (3) complex collective behavior, and (4) use dynamical processes.

This presentation highlights two ongoing computational research efforts, conducted in close collaboration with experimental partners, to prototype synthetic materials that exhibit biologically inspired behaviors at the colloidal scale. The first, the “Oleg MURI Reconfiguration” project, focuses on coarse-grained simulations of reconfigurable, hierarchical DNA lattices. The second, the “Flexicle” project, centers on modeling the mechanics and dynamics of cell-like synthetic structures that mimic key features of biological membranes. In both projects, theory and simulation are deeply integrated with experimental design and validation, enabling iterative development of materials that capture the complexity of biological systems. While the systems of interest for both projects are vastly different, each exemplifies the four core characteristics of adaptive biological materials and contributes to the advancement of tunable, multifunctional soft robotic matter at the colloidal scale.

June 5th, 2025 --- 12:00 PM Eastern --- West Hall 335

Optically Manipulating the Interaction Between Electron and Nuclear Spins in Solid State Systems

Estefanio Kesto

Third Year, Department of Physics

Everything around us is made up of compounds – but remember, compounds are made of elements, and elements are made of atoms! When you zoom all the way into the guts of an atom, you’ll find they’re made up of electrons energetically racing around a nucleus. In our group, we’re interested in how the electrons and nuclei interact in a semiconducting compound known as gallium arsenide (GaAs). Our lab has the capability of exciting, manipulating, and interrogating the electrons’ behavior using a pulsed laser system. What we specifically excite is something known as electron spin polarization, and it turns out that we can tailor our optical scheme to force the electrons to interact with the nuclei through a process known as dynamic nuclear polarization (DNP). Conventionally, electron and nuclear spins interacting through DNP by a pulsed laser have periodic properties. However, in a recent experiment, we have found that this periodicity can be manipulated using unconventional methods. In this talk, I’ll first introduce some semiconductor concepts in addition to the conventional optical techniques utilized to generate these effects. Following the introduction, we will jump into the unconventional way our lab recently used to manipulate the electron-nuclear spin interactions. 

Together, we will be exploring the relationship between optically excited electron and nuclear spins!

June 12th, 2025 --- 12:00 PM Eastern --- West Hall 335

No seminar on June 19th, 2025 in observance of Juneteenth

Effective Field Theory of Modified Gravity: Initial Conditions and Cosmological Constraints 

Jiaming Pan

Third Year, Department of Physics

Recent cosmological observations — including data from DESI baryon acoustic oscillation and the cosmic microwave background — suggest that dark energy is not behaving as a cosmological constant but may be evolving with time. In this talk, I will show how these phenomena can be interpreted as a hint for modifications to Einstein’s theory of gravity on cosmological scales. In particular, I will present a ~3 sigma indication that gravity is non-minimally coupled to matter in the latest observations using model-independent analysis. This result represents a test of modified gravity in the late universe.

To extend such tests to the early universe, however, it is essential to model cosmological initial conditions accurately. I will show that, in modified gravity models, the standard initial conditions derived from general relativity may no longer be valid, and using them can lead to significant biases in cosmological predictions, including the cosmic microwave background. I will present how to derive and implement consistent initial conditions for modified gravity models, and illustrate their impact on cosmological observables.

June 26th, 2025 --- 12:00 PM Eastern --- West Hall 335

Measuring the Missing Energy of Neutrinos Due to Nuclear Interactions 

Cassandra Little

Fifth Year, Department of Physics

As modern neutrino experiments become increasingly precise, a better understanding of neutrino interaction physics becomes a necessity for controlling uncertainties. Kaon decay at rest (KDAR; $K^+\rightarrow\mu^+\nu_\mu$) produces a monoenergetic neutrino with a known energy (235.5 MeV) which could be used to observe the energy lost in a neutrino-nucleus interaction. The J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source experiment (JSNS²) observes the monoenergetic neutrino interaction $\nu_\mu^{12}C\rightarrow\mu^{- 12}N$ or $\nu_\mu n\rightarrow\mu^- p$ and defines the missing neutrino energy as the energy that is transferred to the nucleus minus the kinetic energy of the outgoing proton. Naively, this missing energy is expected to be zero, but nuclear interactions and processes (e.g. nucleon separation energy, Fermi momenta, and final-state interactions) are uniquely reflected. The shape only, differential cross section is presented from 621 events, based on a 77 ± 3 % pure double coincidence KDAR signal. This measurement provides detailed insight into the neutrino-nucleus interaction, even allowing the nuclear orbital shell of the struck nucleon to be inferred. This measurement provides an important benchmark for models and event generators in the hundreds of MeV region, a difficult to model area that transitions between neutrino-nucleus and neutrino-nucleon scattering. It additionally benefits neutrino oscillation measurements, nuclear physics, and Type-II supernova studies.

July 3rd, 2025 --- 12:00 PM Eastern --- West Hall 335

Collinear Multidimensional Coherent Spectroscopy with Imaging on Atomically Thin Transition Metal Dichalcogenides

Blake Hipsley

Sixth Year, Department of Physics

(more information coming soon)

July 10th, 2025 --- 12:00 PM Eastern --- West Hall 335

Gravitational-Wave Cosmology with Standard Sirens: Eyes and Ears on Stellar Collisions

Simran Kaur

Third Year, Department of Physics

Gravitational waves from compact object mergers offer a new way to measure the expansion of the universe using “standard sirens.” In this talk, I will introduce the science of gravitational-wave cosmology and the role of electromagnetic (EM) counterparts in improving distance measurements. I will present recent efforts to follow up O4 gravitational-wave events using DECam, highlighting both challenges and successes in identifying potential EM candidates. Looking ahead, I will discuss forecasts for the Rubin Observatory’s LSST and its potential to dramatically increase the number of EM counterparts detected, thereby tightening constraints on cosmological parameters such as the Hubble constant. Together, these efforts demonstrate the growing power of multi-messenger astronomy to probe the dynamics and fate of our universe.

July 17th, 2025 --- 12:00 PM Eastern --- West Hall 335

Measurement of the Xenon-129 EDM

Henry Sottrel

Second Year, Department of Physics

(more information coming soon)

August 7th, 2025 --- 12:00 PM Eastern --- West Hall 335

Renormalisation on Networks

Connie Sheeran

First Year, Department of Physics

(more information coming soon)

August 14th, 2025 --- 12:00 PM Eastern --- West Hall 335

Interested in signing up to give a PGSS talk? Applications for 2025 are closed, but be on the lookout for the 2026 application next spring!

(Note: You must be a graduate student at the University of Michigan Ann Arbor to be eligible)