Dartmouth Events

Abstract: Compact objects, such as black holes and neutron stars, are known to be surrounded by dense clouds of particles, including but not limited to photons, various plasmas, and potentially dark matter and gravitons. These environments are of immense research interest, not only for the purpose of understanding the compact objects they surround, but also in the search to identify new particles, especially dark matter. However, certain particle physics calculations are well developed in flat spacetime but intractable in curved spacetime. In this thesis, I present a formalism by which some of these calculations may be made tractable within a perturbative series. The formalism works by constructing small patches of locally flat spacetime, through which a particle travels; as a particle goes from one patch to another, the effective Lagrangian receives corrections for each patch. One application for this that we explore is particle mixing, a phenomenon whereby one species of particle can oscillate into another species. Specifically examining bosonic Primakoff mixing, where mixing is driven by a background field, we find that, as a boson travels through curved spacetime, its mixing angles may change as a function of the number of patches through which it travels. Calculations of mixing in the vicinity of a compact object must account for these curvature corrections.

This thesis also explores another topic in the area of particle behavior around a compact object, namely that of axion lasers produced by superradiance. Superradiance, a phenomenon through which energy and angular momentum may be extracted from a rotating black hole, can generate dense clouds of axions, which can then decay into photons; the number of photons produced by this decay can stimulate further decay, creating a laser. This laser is powerful enough that the Schwinger effect may become significant, producing an electron-positron plasma, which has the effect of slowing axion decay by imparting photons with an effective mass. In a simplified model, we find, depending on the system’s parameters, that the equilibrium state of this laser may be mildly enhanced, or it may become unable to reach equilibrium, with the axion cloud continuing to grow superradiantly.

PhD Thesis Advisor: Professor Deven Walker