Probing Models of Dark Matter and the Early Universe

[摘要] This thesis discusses models for dark matter (DM) and their behavior in the early universe.An important question is how phenomenological probes can directly search for signals of DM today.Another topic of investigation is how the DM and other processes in the early universe must evolve.Then, astrophysical bounds on early universe dynamics can constrain DM.We will consider these questions in the context of three classes of DM models---weakly interacting massive particles (WIMPs), axions, and primordial black holes (PBHs).Starting with WIMPs, we consider models where the DM is charged under the electroweak gauge group of the Standard Model.Such WIMPs, if generated by a thermal cosmological history, are constrained by direct detection experiments.To avoid present or near-future bounds, the WIMP model or cosmological history must be altered in some way.This may be accomplished by the inclusion of new states that coannihilate with the WIMP or a period of non-thermal evolution in the early universe.Future experiments are likely to probe some of these altered scenarios, and a non-observation would require a high degree of tuning in some of the model parameters in these scenarios.Next, axions, as light pseudo-Nambu-Goldstone bosons, are susceptible to quantum fluctuations in the early universe that lead to isocurvature perturbations, which are constrained by observations of the cosmic microwave background (CMB).We ask what it would take to allow axion models in the face of these strong CMB bounds.We revisit models where inflationary dynamics modify the axion potential and discuss how isocurvature bounds can be relaxed, elucidating the difficulties in these constructions.Avoiding disruption of inflationary dynamics provides important limits on the parameter space.Finally, PBHs have received interest in part due to observations by LIGO of merging black hole binaries.We ask how these PBHs could arise through inflationary models and investigate the opportunity for corroboration through experimental probes of gravitational waves at pulsar timing arrays.We provide examples of theories that are already ruled out, theories that will soon be probed, and theories that will not be tested in the foreseeable future.The models that are most strongly constrained are those with relatively broad primordial power spectra.

[发布机构] University of Michigan

[效力级别] Dark matter

[关键词] Theoretical high-energy physics - phenomenology;Dark matter;Early universe cosmology;Axion;Primordial black holes;Inflation;Physics;Science;Physics