CAREER: Illuminating the Early Universe with Dark Matter

University Of North Carolina At Chapel Hill, Chapel Hill NC

Investigators

Abstract

This CAREER award funds the research activities of Professor Adrienne Erickcek at the University of North Carolina at Chapel Hill. Observations of the oldest light in the Universe indicate that there was a period of accelerated expansion, called inflation, shortly after the Big Bang. During inflation, quantum fluctuations in the energy density of the Universe were imprinted on cosmological scales, seeding the structures that eventually became galaxies. We do not know why inflation happened or why it ended. Moreover, inflation left the Universe devoid of all matter and radiation, yet the measured abundances of light elements imply that the Universe was filled with extremely hot radiation one second after inflation ended. Professor Erickcek aims to fill this gap in the cosmological record by studying the smallest gravitationally bound clumps of dark matter, which is an unknown source of mass that currently makes up about 25% of the energy density of the Universe. In addition to improving our understanding of the early Universe and the properties of dark matter --- thus advancing the national interest by promoting the progress of science --- this project will also have significant broader impacts. Graduate and undergraduate students will contribute to this investigation and will receive training both in physical cosmology and in widely applicable mathematical and computational techniques. Professor Erickcek will also bring the excitement of this research to high-school students by working with educators at the Morehead Planetarium and Science Center to develop an inquiry-based curriculum module that incorporates the evidence for dark matter into lessons on Newtonian mechanics, thereby exposing students to one of the great mysteries of cosmology. This module will be made publicly available, and Professor Erickcek will lead professional-development workshops at North Carolina teaching conferences to train high-school teachers to use this module in their classrooms. Finally, Professor Erickcek will share her research with the general public by hosting Morehead's Carolina Science Cafe and Teen Science Cafe. More specifically, the smallest and earliest-forming dark matter halos provide a window into the gap between inflation and the hot Big Bang because their abundance is affected by the properties of the density fluctuations created during the final stages of inflation and the evolution of the Universe during its first second. Professor Erickcek will extend her prior work on how gamma-ray observations constrain thermal dark-matter production during an early matter-dominated era to other thermal histories and dark-matter creation mechanisms. This investigation will narrow the field of potential dark-matter candidates by restricting their production mechanisms and breaking the degeneracy between relic abundance and thermal history. In particular, it will determine if gravitationally coupled moduli fields with masses around the TeV scale are compatible with neutralino dark matter, and may rule out super-heavy hidden-sector particles as dark-matter candidates. This investigation will also determine how enhanced small-scale inhomogeneity generated during inflation affects the microhalo abundance and the dark-matter annihilation rate. Professor Erickcek's group will then derive robust constraints on small-scale primordial fluctuations that will improve our understanding of inflation. Both of these tasks will utilize small-box, high-redshift simulations of microhalo formation. Finally, Professor Erickcek will explore how observations of the cosmic microwave background, 21cm tomography, and measurements of the temperature of the intergalactic medium may expose the existence of early-forming microhalos and allow us to close this gap in our understanding of the early Universe. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.