Research Outputs
The Numbers at a Glance
For more information about my public talks, see the Public Engagement section.
Papers
2024
K. Schumacher et al., "Visualizing polarization effects of gravitational waves using particle rings and surfaces in virtual reality", to appear in ISVC, 2024.
In some modified theories of gravity, gravitational waves may contain up to six polarizations. These different polarizations determine the pattern with Given the multi-dimensional nature of these distortions and the fact that they are not visible to the naked eye, immersive virtual reality is a useful tool for visualizing them. In this work, we introduce what we believe is the first visualization tool allowing users to explore all six gravitational wave polarizations. This interactive and immersive virtual reality experience features three different visualization modes intended to illustrate the different patterns of distortion for each polarization, for arbitrary combinations of the polarizations, and for combinations of polarizations that correspond to specific theories of gravity.
2023
K. Schumacher, S. Perkins, A. Shaw, K. Yagi, and N. Yunes, "Gravitational wave constraints on Einstein-æther theory with LIGO/Virgo data", Phys. Rev. D, 108, 104053 (2023).
Lorentz symmetry is a fundamental property of Einstein’s theory of general relativity that one may wish to test with gravitational wave observations. Einstein-æther theory is a model that introduces Lorentz-symmetry breaking in the gravitational sector through an æther vector field, while still leading to second-order field equations. This well-posed theory passes particle physics constraints because it modifies directly only the gravitational sector, yet it predicts deviations in the inspiral and coalescence of compact objects. We here, for the first time, put this theory to the test by comparing its gravitational wave predictions directly against LIGO/Virgo gravitational wave data. We first construct a waveform model for Einstein-æther theory, EA_IMRPhenomD_NRT, through modifications of the general relativity IMRPhenomD_NRTidalv2 model (used by the LIGO/VIRGO collaboration). This model constructs a response function that not only contains the transverse-traceless polarization but also additional Einstein-æther (scalar and vectorial) polarizations simultaneously. We then use the many current constraints on the theory to construct nontrivial priors for the Einstein-æther coupling constants. After testing the waveform model, we conduct parameter estimation studies on two gravitational wave events: GW170817 and GW190425. We find that these data are not sufficiently informative to place constraints on the theory that are stronger than current bounds from binary pulsar, Solar System, and cosmological observations. This is because, although Einstein-æther modifications include additional polarizations and have been computed beyond leading post-Newtonian order, these modifications are dominated by (already-constrained) dipole effects. These difficulties make it unclear whether future gravitational wave observations will be able to improve on current constraints on Einstein-æther theory.
2023
K. Schumacher, N. Yunes, and K. Yagi, "Gravitational wave polarizations with different propagation speeds", Phys. Rev. D, 108, 104038 (2023).
In some modified theories of gravity, gravitational waves can contain up to six different polarizations, which can travel at speeds different from that of light. Searches for these different polarizations in gravitational wave data are important because any detection would be clear evidence of new physics, while clear nondetections could constrain some modified theories. The first step toward searching the data for such gravitational wave content is the calculation of the amplitudes of these different polarizations. Here we present a model-independent method to obtain the different polarizations of gravitational waves directly from the metric perturbation in theories where these polarizations are allowed to travel at different speeds. We develop our calculations so that the same procedure works with either the metric perturbation itself or its trace-reversed form. Our results are in agreement with previous work in the limit that all polarization speeds are the speed of light. We demonstrate how our model-independent method can be used with two specific modified theories of gravity, suggesting its wide applicability to other theories that allow for different gravitational wave propagation speeds. We further extend the parametrized post-Einsteinian formalism to apply to such theories that travel with different speeds. Finally, we discuss how the different speeds of different polarizations may affect null stream tests of general relativity with gravitational wave observations by multiple interferometers. Differences in propagation speeds may make null streams ineffective or lead to the detection of what seem to be isolated scalar or vector modes.
K. Schumacher et al., "GR in VR: Using immersive virtual reality as a learning tool for general relativity", American Society for Engineering Education 2023 Annual Conference and Exposition, Conference Proceedings (2023).
2023
According to general relativity, gravity can be understood as a curvature of spacetime in response to the presence of matter and energy. Students often struggle to visualize the geometry of curved spacetime. The standard demonstration used to aid in visualization, that of a ball on an elastic sheet, is fundamentally flawed and may lead to misconceptions. Recent research suggests that virtual reality can improve understanding of spatially complex or abstract concepts. We hypothesize that an interactive virtual reality demonstration involving masses in a curved 3D spatial grid, with clocks representing the relative passage of time, would support improved conceptual understanding and impact attitude among students learning general relativity compared to traditional methods. To test this hypothesis, undergraduate students who have no formal experience with general relativity are recruited to evaluate the virtual reality simulation. The students first take a questionnaire to determine a baseline for their conceptual understanding of general relativity, with confidence-scaled multiple choice and written response questions. The experimental group experiences an interactive virtual reality demonstration in which the subjects can move objects through space and time to visualize how mass curves spacetime. An instructor leads the control group through the standard ball on a sheet demo while delivering content orally. Students in both groups are prompted by an instructor to explore the relationship between mass, gravity, and time, guided by a set of conceptual questions. Immediately after the demonstrations, students complete the same questionnaire and a survey about learner attitude and simulation usability. Few previous studies focus on the conceptual understanding of general relativity and even fewer examine the possibility of immersive learning as a tool for teaching this topic. Our work addresses this gap by designing a novel immersive technique for visualizing relativistic effects and comparing this technique to existing non-immersive methods of instruction.
2023
F. Abdi et al., "Mu2e Run I Sensitivity Projections for the Neutrinoless 𝜇−→𝑒− Conversion Search in Aluminum", Universe 9, 54 (2023).
The Mu2e experiment at Fermilab will search for the neutrinoless 𝜇−→𝑒− conversion in the field of an aluminum nucleus. The Mu2e data-taking plan assumes two running periods, Run I and Run II, separated by an approximately two-year-long shutdown. This paper presents an estimate of the expected Mu2e Run I search sensitivity and includes a detailed discussion of the background sources, uncertainties of their prediction, analysis procedures, and the optimization of the experimental sensitivity. The expected Run I 5𝜎 discovery sensitivity is 𝑅𝜇𝑒=1.2×10−15, with a total expected background of 0.11±0.03 events. In the absence of a signal, the expected upper limit is 𝑅𝜇𝑒<6.2×10−16 at 90% CL. This represents a three order of magnitude improvement over the current experimental limit of 𝑅𝜇𝑒
2020
J. Zimmerman, Z. Carson, K. Schumacher, A. W. Steiner, and K. Yagi, "Measuring Nuclear Matter Parameters with Nicer and LIGO/Virgo", arXiv:2002.03210 (2020).
The NICER Collaboration recently reported the measurement of the mass and radius of a pulsar PSR J0030+0451. We here use this new measurement to constrain one of the higher-order nuclear matter parameters Ksym,0. We further combine the tidal measurement of the binary neutron star merger GW170817 by LIGO/Virgo to derive a joint 1-σ constraint as Ksym,0=−102+71−72 MeV. We believe this is the most reliable bound on the parameter to date under the assumption that there is no new physics above the saturation density which impacts neutron star observations.
Invited Presentations
2025
Better early than never: a new test for superluminal gravitational wave polarizations, Theoretical AstroPhysics Including Relativity Seminar, California Institute of Technology.
2024
Better early than never: Testing GR with GW polarizations, Kavli Institute for Cosmological Physics Seminar, University of Chicago.
2024
Better early than never: Testing GR with GW polarizations, Astrophysics, Relativity and Cosmology Seminar, University of Illinois Urbana-Champaign.
2023
STEAM Education into the 2030's Panel, American Society for Engineering Education Annual Conference, Baltimore, MD.
2023
Theoretical Physics Panel, Conference for Undergraduate Women in Physics, University of Illinois Urbana-Champaign.
Contributed Presentations
Midwest Relativity Meeting, 2024
Better Early than Never: Testing GR with GW Polarizations
Midwest Relativity Meeting, 2023
Better early than never: Testing GR with GW polarizations
April APS, 2023
Converging to the wrong answer: Robustness of theory-specific GW tests of GR
April APS, 2022
Constructing a waveform template for Einstein-æther theory
April APS, 2024
Better Early than Never: Testing GR with GW Polarizations
ASEE Annual Conference and Exposition, 2023
GR in VR: Using immersive virtual reality as a learning tool for general relativity
Midwest Relativity Meeting, 2022
Gravitational wave constraints on Einstein-æther theory
Midwest Relativity Meeting, 2021
Constructing a waveform template for Einstein-æther theory
Posters
Illinois Center for Advanced Studies of the Universe Inaugural Conference, 2022
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Constructing a waveform template for Einstein-æther theory
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Physics Outreach at Illinois through New Technologies
Conference for Undergraduate Women in Physics, 2018
A cosmic ray telescope to measure muon flux at Mu2e
APS Southeastern Section, 2018
Cosmic ray telescope measurements of muon flux at Mu2e