# First Postdoctoral and Graduate Student Fellows Named by Leinweber Center for Theoretical Physics

The Leinweber Center for Theoretical Physics (LCTP) was established in 2017 following an $8 million endowment from the Leinweber Foundation, led by Larry Leinweber and Claudia Babiarz.

Members of LCTP, formerly the Michigan Center for Theoretical Physics, focus on fundamental topics in particle physics and cosmology, including the identity of the dark matter, string theory, black holes, and the evolution of our universe. The formation of LCTP established support for students, researchers, and visiting scholars with the aim of promoting new discoveries in fundamental physics and attracting top researchers to Michigan Physics.

The first ever Leinweber Postdoctoral Fellow is Dr. Andrew Long. In addition, four Michigan graduate students have been awarded the first Leinweber Graduate Fellowships, a year-long award which allows students to focus on research. The fellowship is awarded to students working on questions in fundamental theoretical physics who demonstrate “academic achievement and potential for leadership.” Recipients of this year’s fellowships are Josh Foster, Juliette Becker, Sangmin Choi, and Callum Jones.

Commenting on this year’s fellows, Larry Leinweber says, “I have been consistently impressed and enthused by the caliber of LCTP Fellows at Michigan Physics I have met. Their passion for their work and commitment to basic research is so vital to the future of physics, science, and advancing the frontiers of knowledge.”

**Dr. Andrew Long**, the 2018-2019 Leinweber Postdoctoral Fellow, works on questions at the interface between theoretical cosmology and particle physics. One of Dr. Long’s research interests is the matter-antimatter asymmetry, or understanding why there is more matter than antimatter in the universe. He has studied how more precise measurements of the Higgs boson might shed light on this problem. Another topic of interest to Dr. Long is dark matter, which makes up the majority of particles in the universe but has still not been understood. Related open questions that he studies include how dark matter formed in the early universe as well as the identity of dark matter particles. Dr. Long has also studied how the universe’s background magnetic field may have been formed in the early universe and how this could be tested experimentally.

Dr. Long received his Ph.D. from the University of Wisconsin. He previously was a Postdoctoral Fellow at the Kavli Institute for Cosmological Physics at the University of Chicago and a Postdoctoral Researcher at the University of Arizona. In 2019, he will be a faculty member at Rice University.

One Leinweber Graduate Fellowship recipient is **Josh Foster**. He is a third-year graduate student in physics working with Professor Ben Safdi studying dark matter. Mr. Foster is interested in understanding how the particle physics properties of dark matter affect its cosmological history and determine its current structure and distribution. He investigates this question through a joint application of theoretical and computational techniques. Answering this question has important implications for efforts to detect dark matter, and Mr. Foster is interested in the development of new search strategies alongside the analysis and interpretation of current experiments. He also studies how extreme astrophysical environments, such as those found in neutron stars, could provide new methods to detect dark matter. In the future, Mr. Foster also plans to work on developing statistical techniques to study dark matter properties in large astrophysical datasets and to build models of dark matter within the context of existing particle physics and cosmological anomalies.

Fifth-year astronomy graduate student **Juliette Becker**, another Leinweber fellowship recipient, works with Professor Fred Adams. Ms. Becker’s area of interest is in astrophysical dynamics, specifically in studying the orbits of planets, as well as how the orbits interact with each other and are influenced by other bodies like stars. She has used dynamical calculations to indicate the existence of exoplanets, or planets in other solar systems, leading to the discovery of two planets in the WASP-47 system, six planets in the K2-226 system, and five planets in the HIP 41378 system. In our solar system, Ms. Becker is interested in understanding the outermost regions, where she has contributed to the discovery of an object with an extreme orbit that may suggest the existence of planets beyond Pluto. She also studies the Kuiper Belt and Oort Cloud, two regions of icy objects in the outer solar system. Results from this work could lead to a better understanding of how the solar system formed. Currently, Ms. Becker is working on systems discovered by a new planet-hunting spacecraft called the Transiting Exoplanet Survey Satellite (TESS), and she plans to continue this work in the future.

**Sangmin Choi**, also a recipient of a Leinweber fellowship, is a third-year graduate student in physics working with Professor Ratindranath Akhoury. He is interested in long-range interactions in quantum field theories including quantum electrodynamics (QED) and perturbative quantum gravity. QED is the modern theory of electrodynamics that incorporates both quantum mechanics and special relativity to describe interactions between charged particles like electrons. In quantum field theories, interactions are facilitated by gauge particles; for example, in QED, the interaction between two electrons occurs via a photon. Mr. Choi’s work considers clouds of low-energy gauge particles, including photons, introduced by long-range interactions. These particle clouds can be used to study quantum states on the event horizon of black holes, or the “boundary” of the black hole beyond which light and objects cannot escape. Mr. Choi has previously studied these clouds using QED and is currently working on extending these studies to perturbative quantum gravity with the goal of understanding more about consequences of long-range interactions.

The final recipient of the Leinweber fellowship, **Callum Jones**, is a fourth-year graduate student in physics working with Professor Henriette Elvang on developing simpler and more efficient mathematical and computational machinery to describe particle physics in the Standard Model and beyond. The Standard Model is the current theory for fundamental particles and their interactions, and in principle it can be used to predict any quantity relating to particle behavior. The usual method used to do this employs Feynman diagrams, where symbols are used to represent the mathematics behind particle interactions, but this method is often so complex that very precise calculations are virtually impossible. Instead, Mr. Jones uses on-shell methods, a modern approach which emphasizes fundamental symmetries. This approach has allowed him to understand the emission of low energy electromagnetic and gravitational radiation, a problem which was first investigated more than 50 years ago. The complexity of the Feynman diagram method made it difficult to fully explore this problem, but by using on-shell methods Mr. Jones was able to find a simple general solution. He has also applied these methods to the classification of low energy particle physics theories, leading to new knowledge about existing theories as well as the discovery of new models of particles and interactions.

Professor Aaron Pierce, Director of LCTP, says, “I am delighted to have such a fantastic group as our first class of Leinweber Fellows, and am excited to see the advances that come from their research. This is an exciting time for the center, and I am eager to see it grow and develop in the coming years.”

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