The first direct observations of gravitational waves (GWs) by the LIGO and Virgo interferometers in 2016 confirmed the predictions of general relativity for the dynamics of black hole mergers, and has since advanced the field of GW astronomy. These interferometers focus on detecting GWs in the Hz-kHz frequency range. There are no known astrophysical objects that emit beyond the 10 kHz range, motivating an interest in detectors for frequencies above this range which could lead to the discovery of new physics beyond the Standard Model. Theoretical potential sources of these high frequency GWs include mergers of sub-solar mass objects such as primordial black holes (PBH) or boson clouds from PBH superradiance. Resonant microwave cavity detectors such as the detector used in ADMX are shown to be sensitive to GWs in the GHz range, and generate a coherent electromagnetic (EM) signal through the GW-EM coupling if the GW frequency matches the cavity resonance frequency. To detect these signals, I use a matched filtering technique on power measurements collected from the cavity during ADMX’s Run 1B data acquisition period in 2018. I generated templates for a range of frequencies based on an expected signal a PBH merger would emit and convolved it with the data to find similar signals. This analysis may confirm or further constrain the existence of PBH sources within the GHz frequency range. PBHs could comprise a significant fraction of cold dark matter, and its detection allows us to probe the density fluctuations and phase transitions of the early universe with implications in galaxy formation and supermassive black hole formation.

Blackbody radiation is the name given to the phenomenon that makes warm objects radiate—it explains why a hot stove glows red, or why the sun is so bright. This radiation is well-understood in physics, but some theories of new particles suggest that at low temperatures there will be small deviations to the equations that normally predict the amount of power radiated by these bodies. I am conducting an experiment designed to search for these deviations. This experiment will involve measuring the radiated microwave power from a resonant cavity and a resistor as they are cooled to liquid nitrogen temperatures; standard physics predicts these power values scale linearly with temperature, which is the expected result. However, some expanded standard model theories predict a deficit of power at low temperatures due mixing of photons with new light particles. This research will help refine our understanding of blackbody radiation at low temperatures, including our understanding of the results from the UW Axion Dark Matter eXperiment (ADMX).

The axion is a hypothetical elementary particle beyond the Standard Model which serves as a candidate for dark matter, a mysterious form of matter that accounts for about 85 percent of total matter in the universe and is difficult to detect by conventional means due to its noninteracting nature with electromagnetic radiation. The ADMX (Axion Dark Matter eXperiment) is an axion haloscope which uses a strong magnetic field to convert axions inside a microwave resonant cavity into microwave photons that could be registered by the detector when the photon signal frequency is the same as the cavity’s resonant frequency. However, within a dataset, the axion signal can be hard to estimate and pinpoint due to the presence of RFI(radio frequency interference).In our research, we developed a new two-parameter statistical model that accounts for RFI appearance and estimates both the axion signal and RFI from a dataset. We show that contrary to the old one-parameter statistical model, which is currently utilized for processing datasets and does not account for RFI appearance, the new two-parameter model yields more accurate and consistent axion signal results regardless of RFI magnitude while the old one-parameter model fails to provide reasonable results at large RFI frequencies. The new two-parameter model would benefit ADMX by providing greater overall accuracy and precision for the search of axion dark matter signals and faster scan speeds.