This award funds the research activities of Professor Adrienne Erickcek at the University of North Carolina at Chapel Hill.
The evolution of the Universe during its first second is unknown. While there is strong evidence that the Universe's first second included a period of accelerated expansion called inflation, we do know why inflation happened or why it ended. We also do not know how the Universe transitioned to a hot, radiation-dominated state after inflation. Furthermore, our ignorance of the dynamics of the early Universe severely limits our understanding of the origins of dark matter, which is a poorly understood source of mass that currently makes up about 25% of the Universe's energy density. Many proposed explanations for dark matter postulate that dark matter originated from the hot plasma that filled the Universe during its first second. Consequently, the evolution of the Universe during that time affects the relationship between the properties of the dark matter particle and amount of dark matter in the Universe. This project will enhance our understanding of inflation, the onset of radiation domination, and the origins of dark matter by using gamma-ray observations to constrain the abundance of the smallest gravitationally bound structures of dark matter.
The PI will engage undergraduate students, high school students, and the general public in the proposed investigation of dark matter microhalos. Undergraduate students will analyze simulations of microhalo formation, thereby learning data analysis techniques and scientific programming. They will also gain first-hand research experience, which will expose them to the excitement of STEM careers. A module on dark matter will be developed for high school students to give them the opportunity to analyze publically available kinematic data for dwarf spheroidal and spiral galaxies. The PI will then lead four professional development workshops at teacher conferences to train high school teachers to use this module in their physics courses. Finally, the PI will present her research at Morehead?s monthly Carolina Science Cafe, which provides the general public the opportunity to interact with a scientific researcher in an informal setting.
These small dark matter structures, called microhalos, grow from density perturbations that were generated during inflation on scales that are inaccessible by other cosmological observations. They also began to evolve during the Universe's first second, prior to the onset of nucleosynthesis. This project will extend the PI's earlier analyses of microhalos' capacity to probe the evolution of the early Universe to a wider range of dark matter particles and will use N-body simulations of small volumes at high redshifts to test these analytical predictions for the microhalo abundance. These simulations will also determine how the properties of the small-scale density perturbations affect the microhalos' internal structures. The PI will then calculate the expected gamma-ray emission from dark matter annihilation within these microhalos. The resulting constraints on the small-scale primordial density fluctuations and the onset of radiation domination will determine which inflationary models are compatible with thermal-relic dark matter and may break the degeneracy between the relic density of dark matter and the evolution of the early Universe.
