The Standard Model of particle physics is known to be incomplete, and many extensions and modifications have been proposed to resolve outstanding issues. In order to discriminate which of these many ideas may be correct, we seek novel approaches to acquire new data and apply old data. The research in this dissertation advances these efforts, probing physics beyond the Standard Model in three distinct ways. First, we propose a novel design of a laboratory search for axions based on photon regeneration with superconducting radiofrequency resonant cavities. We use a confined static magnetic field to avoid degrading the large resonant quality factors. After analysis of fundamental issues and limitations, we conclude this design can potentially probe axion-photon couplings beyond astrophysical limits, comparable and complementary to next generation optical experiments. Second, we demonstrate that rotational superradiance can be efficient in millisecond pulsars. We use measurements from the two fastest known pulsars to place bounds on bosons with masses below 10^−11 eV and Yukawa couplings to neutrons, exceeding fifth force constraints by 3 orders of magnitude for masses near the pulsar rotation rates. For certain neutron star equations of state, these measurements also constrain the QCD axion. Third, we consider dark matter (DM) candidates that heat white dwarfs through the production of high-energy Standard Model (SM) particles, and show that such particles will efficiently thermalize the stellar medium and ignite type Ia supernovae. Based on the existence of long-lived white dwarfs and the observed supernovae rate, we derive new constraints on DM with masses greater than 10^16 GeV which produce SM particles through DM-DM annihilations, DM decays, and DM-SM scattering interactions in the stellar medium.

The empirical study of ultraheavy dark matter (DM) requires astrophysical probes. We present here a detailed study of DM-induced type Ia supernovae as one such probe. Dark matter may heat a small region in a white dwarf (WD) sufficient to trigger runaway fusion and ignite a supernova. We consider DM candidates that heat through the production of high-energy standard model (SM) particles, and show that such particles efficiently thermalize the WD medium and ignite supernovae. Based on the existence of long-lived WDs and the observed supernovae rate, we put new constraints on ultra-heavy DM candidates with masses above 10^{16} GeV that produce SM particles through annihilation, decay, and DM-SM scattering in the stellar medium. As a concrete example, this rules out supersymmetric Q-ball DM in parameter space complementary to terrestrial bounds. We further consider the possibility of DM capture by WDs, leading to the formation and self-gravitational collapse of a DM core within the star. This process allows two additional mechanisms for DM-induced particle heating, which we study here. For asymmetric DM, such a core may form a black hole that ignites a supernovae via Hawking radiation. For DM with a sufficiently small but nonzero annihilation cross section the core may cause ignition via a burst of annihilation during gravitational collapse. These processes are sensitive to much less massive candidates, down to 10^7 GeV, than are the mechanisms involving a single DM particle. It is also intriguing that these DM-induced ignition scenarios provide an alternative mechanism of triggering supernovae from sub-Chandrasekhar mass progenitors.

We present three distinct pathways for theory and experiment beyond the Standard Model. First, we propose an experimental design of a laboratory search for axions based on photon regeneration with superconducting RF cavities. We then study a novel production mechanism for ultralight vector dark matter in the early universe based on a parametric resonance instability. Finally, we show that white dwarfs are in fact ideal detectors of ultra-heavy DM over large regions of parameter space.