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Presented By: Department Colloquia

Department Colloquium | Graduate Student Showcase

Nora Sherman, Torben Purz, Aidan Herderschee (U-M Physics)

Nora Sherman (U-M Physics)

A Multi-Messenger Search for H0 Using Optical Counterparts to Gravitational Wave Events

Measurements of the Hubble Constant (H0) – a parameter that helps illustrate the expanding behavior of the universe – differ vastly, particularly between those using early- versus late-universe data. To help relieve this tension, the Dark Energy Survey Gravitational Wave group (DESGW) seeks to perform a standard siren measurement of H0 by identifying electromagnetic counterparts to compact binary mergers. Together with the GW data from detections by the LIGO/Virgo/KAGRA Collaboration (LVK), this information allows us to make an H0 measurement independent of traditional methods. In this talk, I will detail DESGW’s pursuit of this measurement, including our tools for observation and analysis, recent key results, ongoing studies critical to the project, and our preparation for the next LVK observing run.

Torben Purz (U-M Physics)

Imaging of Dynamic Exciton Interactions and Coupling in Transition Metal Dichalcogenides

Transition metal dichalcogenides (TMDs) are regarded as a possible material platform for quantum information science, photovoltaics, and related device applications. However, many experimental results on TMDs are only realized at specific spots on the sample, presenting a challenge to the scalability of these applications. Here, we demonstrate multi-dimensional coherent imaging spectroscopy on TMD monolayer and heterostructure samples. This technique enables us to shed light on the spatial dynamics of various material parameters—including dephasing, inhomogeneity, and strain, as well as coherent exciton coupling and charge transfer. We demonstrate that dephasing and inhomogeneity are very sensitive to residual strain in state-of-the-art TMD monolayer samples. At the same time, the coherent coupling strength and charge transfer remain robust across large areas of the heterostructure sample. Our findings strengthen the case for heterostructure TMDs as a next-generation material platform for device applications and introduce a powerful tool in multi-dimensional coherent imaging spectroscopy for material characterization.

Aidan Herderschee (U-M Physics)

The Space of Supersymmetric Theories

I will review how causality non-trivially bounds the space of quantum field theories, focusing in particular on maximally supersymmetric theories in four dimensions. I will then discuss some geometric properties of this space and how to efficiently calculate bounds using linear programming. Finally, I will use some results from string theory to motivate novel conjectures.
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