PGSS 2018

Below you will find the list of speakers for the 2018 PGSS.

5/9/2018 1:30 PM 340 West Hall - Dark Matter: A theory status report

Aaron Pierce,  Leinweber Center for Theoretical Physics (LCTP)

The identity of the Dark Matter that dominates the matter density of the universe remains a mystery.  Increasingly sophisticated experiments have begun to probe some of the best motivated models of dark matter.  I will review the theoretical status of one such paradigm, so-called Weakly Interacting Massive Particle (WIMP) Dark Matter, with particular emphasis on the implications of direct detection experiments.  We will see that while the paradigm is alive and well, it is under non-trivial pressure, particularly in specific implementations, such as supersymmetry. This warrants searches for other types of Dark Matter.  Time permitting, I will very briefly discuss a few such searches.

5/16/2018 12:00 PM 340 West Hall - Multidimensional Spectroscopy of Color Centers in Diamond

Matt Day, Physics

Color centers in diamond are a broad class of optically accessible physical systems which, by virtue of being embedded crystal defects in the diamond lattice, are relatively isolated from the macroscopic environment. This makes them promising candidates for a variety of applications from precision metrology to quantum information processing. One key to realizing these applications is a detailed understanding of the electron dynamics that govern the opto-electronic properties of color centers. I will present our recent work studying silicon–vacancy centers with multidimensional coherent spectroscopy, discuss the implications of these results for proposed silicon–vacancy center applications, and mention a few exciting new directions of study in the world of color center spectroscopy.

5/23/2018 12:00 PM 340 West Hall - Eigenstate Thermalization Hypothesis in Spinor Condensates 

Ceren Dag, Physics

Thermalization of isolated quantum systems is a long-standing fundamental problem where different mechanisms are proposed over time. Eigenstate thermalization hypothesis (ETH) is one of the most well-known of these mechanisms. I will start my talk by introducing the problem of quantum thermalization and ETH as a possible route to thermalization. Then I will switch gears and turn to the topic of spinor Bose-Einstein condensates. Eventually the aim of the talk is to answer the question of "Could spinor condensates be another test-bench for testing eigenstate thermalization hypothesis besides widely used quantum many-body systems?". I will show the experimental advantages of spinor condensates to observe ETH and the possible limits of this model. Finally, it seems possible to draw a relation between the thermalization and localization properties of the eigenstates via studying spinor condensates.  

5/30/2018 12:00 PM 340 West Hall - Illuminating Photosynthesis with Two Dimensional Spectroscopy

Riley Sechrist, Physics

Photosynthesis is a process vital to life on Earth by which energy from light is converted to chemical energy. Although much is understood about this process, unanswered questions remain that, if answered, could inspire more efficient artificial light harvesting technologies. The technique of two-dimensional (2D) spectroscopy has shown promise in addressing some of these questions. In this talk, I will discuss 2D studies of the Bacterial Reaction Center (BRC), a pigment-protein complex that serves as a model system for investigating the initial steps of photosynthesis. By exciting the BRC in the near-IR and detecting the response over a broadportion of the visible spectrum, we are able to uncover previously obscured coupling between BRC pigments and begin to further elucidate the kinetic pathways of energy transfer and charge separation. 

6/6/2018 12:00 PM 411 West Hall - Exploring the Origins of Nitrogen in Terrestrial Worlds

Tom Rice, Astronomy

In the study of star and planet formation, one outstanding question is how the materials necessary for life (such as water, carbon, and nitrogen) arrived on rocky worlds like our Earth. In my dissertation, I am studying this topic through observations of young, still-forming solar systems to better understand their chemical compositions. By focusing on nitrogen-bearing organic molecules, and using models of protostellar envelopes, I hope to better understand the origins of the Earth's nitrogen. 

6/13/2018 12:00 PM 411 West Hall - Supermassive black holes as the regulators of star formation in central galaxies

Bryan Terrazas, Astronomy

Cavities and bubbles in the extended X-ray emission from massive galaxies demonstrate that feedback from supermassive black holes can have a profound effect on the hot gaseous atmospheres that surround these systems. The consequences of these effects result in dramatic changes with respect to how the baryon cycle works and whether new stars are able form within these galaxies. With this concern in mind, we present a relationship between the black hole mass, stellar mass, and star formation rate of a diverse group of 91 local galaxies with dynamically-measured black hole masses. For our sample of galaxies with a variety of morphologies and other galactic properties, we find that the specific star formation rate is a smoothly decreasing function of the ratio between black hole mass and stellar mass. With respect to galaxy formation models, our results present a powerful diagnostic with which to test various prescriptions of black hole feedback and its effects on star formation activity. Using the new IllustrisTNG simulation, we illuminate the physics behind quiescence in this model and compare with our observational results. We also use dozens of other TNG runs with varying physics implementations to show how observable galaxy trends and correlations are affected by changes in the black hole feedback physics, thereby providing a pathway to physically interpret observations.

6/20/2018 12:00 PM 340 West Hall - Electromagnetically Induced Transparency 

Michael Viray, Physics

Electromagnetically induced transparency (EIT) is a nonlinear and fully quantum optical phenomenon that occurs in certain atomic systems. EIT drastically alters both the absorption and dispersion of an atomic medium, resulting in unusual optical effects: the medium becomes transparent to wavelengths it usually absorbs, and light itself is slowed down or even stopped. EIT's properties have made it not just an interesting area of research, but also a tool for quantum engineering. In my talk, I will first explain the physical mechanisms behind EIT. I will then talk about Raithel Group's ongoing efforts to use EIT as a quantum-based method for detecting electric fields.

6/27/2018 12:00 PM 340 West Hall - What Is Gromov Witten Theory?

Rachel Webb, Mathematics

The point of my talk is to answer that question. Nevertheless, I will dodge the question twice and give a snarky answer once before proceeding to the meat of the talk (in the last 7 minutes). At the end, you should have a bit of physical and mathematical intuition for what Gromov Witten invariants are and what they can (and can't) tell us, what they can say about the number of lines through two points and about the nature of the universe.

7/11/2018 12:00 PM 340 West Hall - Doubling Scattering Amplitudes

Shruti Paranjape, Physics

Modern particle physics is described via symmetries and scattering amplitudes are the main observables of particle physics. Motivated by this, we will forgo the traditional approach of Lagrangians and Feynman rules, and instead use symmetry-driven techniques to calculate amplitudes. In particular, we will review how gluon amplitudes can be doubled into gravity ones and how this doubling procedure can be extended to other particles. We will exploit this technique to find subleading interactions in theories arising from symmetry-breaking. Double the amplitudes- double the fun!

7/18/2018 12:00 PM 340 West Hall - The MUSE experiment and Proton Radius Puzzle 

Noah Wuerfel, Physics

In 2010, a novel method of spectroscopic measurements on muonic hydrogen resulted in a 4% smaller proton radius than previously observed, and at an order of magnitude improvement in precision. This measurement, and a second in 2013, established the so-called "Proton Radius Puzzle". Now, the MUSE collaboration will simultaneously measure, for the first time, electron and muon scattering of both polarities from a liquid hydrogen target. In this talk, I will survey the physics of the Proton Radius Puzzle, introduce how the proton radius is measured in scattering and spectroscopic experiments, and discuss how the MUSE experiment will fill an important gap in the proton radius data.  

7/25/2018 12:00 PM 340 West Hall - Search for the Rare Kaon Decay, KL→ π0νν

Melissa Hutcheson, Physics

The KOTO experiment at the J-PARC research facility in Tokai, Japan aims to observe and measure the rare decay of the neutral kaon, KL→π0νν. This decay has a very small Standard Model predicted branching ratio of 3 x 10-11 which is why it has never been experimentally observed. While this decay is extremely rare, it is one of the best decays for studying charge-parity violation, which can tell us about the matter and antimatter asymmetry that we see in the universe today. In this talk, I will explain the details of how KOTO searches for this rare decay, and present some new and exciting results from analysis of data collected in 2015. 

8/1/2018 12:00 PM 340 West Hall - Spin Dynamics: Things are Looking Up (and Down)!

Joe Iafrate, Applied Physics

Electron spin has the potential for use in electronic device applications. Before we can expect to see spintronics as part of our everyday lives, researchers must first understand how to generate, manipulate, and measure electron spin polarization in materials of interest. Our group uses optical pump-probe techniques to study spin dynamics in semiconductors such as gallium arsenide and gallium nitride. In this survey, I will introduce you to our current work and highlight how it fits into the bigger picture of spintronics research.

8/8/201812:00 PM 340 West Hall - The Structure of the Proton through Transverse Single Spin Asymmetries

Nicole Lewis, Physics

Quantum Chromodynamics (QCD) is the tremendously successful theory of the strong force at high energies and allows for the interpretation of hadronic collision data around the world.  Traditional perturbative QCD techniques, however, cannot describe bound states of the strong force and much of what we know about the structure of the proton has come from experiments.  In the past 20 years, unexpected results from spin-momentum correlated measurements have allowed QCD to expand into a more complicated, multidimensional picture of the proton.  In this talk I will be  showing how transverse single-spin asymmetries have paved the way for a much richer picture of QCD.   

8/14/2018 12:00 PM 340 West Hall - An Overview of Active Learning

Jack Goetz, Statistics

The traditional setup for modelling is the data has been gathered before the modelling process begins. However in many situations the modeler has some control over what data is gather (or what unlabelled data is labelled). One can take advantage of this by using Active Learning, which is sequentially selecting data to collect based on your current labelled data. In this talk I will introduce the topic and some common uses. I will then explore two very different approaches, both of which provide theoretical guarantees for their selection algorithm.  

8/22/2018 12:00 PM 340 West Hall -  Mind the Gap: Using the Stellar Mass – Halo Mass Relation to understand Galaxy Growth and Cluster Assembly

 Jesse Golden-Marx, Astronomy

A large variance exists in the amplitude of the galaxy cluster Stellar Mass – Halo Mass (SMHM) relation. We find that the magnitude gap between the brightest central galaxy (BCG) and its fourth brightest neighbor accounts for this variance. At fixed halo mass, clusters with higher magnitude gaps have larger BCG stellar masses. This stratification is also observed in semi-analytic simulations of low-redshift clusters; this suggests that this stratification results from the hierarchical growth of BCGs and may link assembly of the halo with BCG growth. We quantify the impact of the magnitude gap in the SMHM relation using a multiplicative stretch factor, which we measure to be significantly non-zero. Including the magnitude gap also significantly reduces the intrinsic scatter in the BCG stellar mass at fixed halo mass. Additionally, hierarchical growth predicts that at higher redshifts fewer mergers have occurred, indicating that the BCG’s stellar mass and magnitude gap should decrease with increasing lookback time.  This suggests that the slope and magnitude gap stretch factor may evolve with redshift.  We test this prediction using SDSS-redMaPPer clusters to measure the SMHM relation’s parameters as a function of redshift to z < 0.3.  Contrary to expectations from semi-analytic galaxy evolution models, we find no evolution. We will discuss our results in the context of hierarchical growth and prior measurements of BCG growth over the redshift range of our sample.