From the Higgs to the Cosmos

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Particle physics is currently in an interesting but puzzling state. On the one hand, the Standard Model (SM) of particle physics has been incredibly successful at explaining an enormous variety of experimental data, from low-energy precision tests to the highest laboratory collision energies ever achieved at the CERN Large Hadron Collider (LHC). On the other hand, the SM is unable to account for the matter content of the universe, which appears to consist mainly of dark matter (DM) followed by an excess of matter over antimatter. The Higgs boson predicted by the SM, and recently discovered at the LHC, also presents and enormous theoretical puzzle in that its mass is extremely sensitive to quantum mechanical corrections. The goal of this proposal is to investigate theories of new elementary particles and forces beyond the SM that can resolve the cosmological shortcomings of the SM and the extreme quantum sensitivity of the Higgs.Dark matter makes up the majority of the matter in the universe. However, the precise nature of DM remains unknown as it has avoided any conclusive detection in laboratory searches or astrophysical observations. A possible reason for this is that DM is more complicated than expected, and the DM particle is only one component of an entire dark sector of particles that interact very feebly with the SM. The first part of this program is the investigation of dark sectors and their possible connection to DM, cosmology, and laboratory experiments. The Higgs boson is the least understood part of the SM. Data obtained so far suggests that the new Higgs particle found at LHC has the properties of the SM Higgs boson, but a program of precision Higgs studies at the LHC and beyond is needed to fully understand this new state. Detailed Higgs measurements will test extensions of the SM that address the puzzle of its mass. Furthermore, searches for exotic Higgs decay channels present a very special opportunity to discover new particles and forces, including those in a dark sector. Motivated by this opportunity, the second part of this program will investigate exotic Higgs decay channels and develop methods to observe them at the LHC and potential future particle colliders.Detailed studies of the Higgs may also help to explain why there is more regular matter than antimatter in the universe. One of the most promising mechanisms to create this matter asymmetry is electroweak baryogenesis, in which baryon creation occurs during the electroweak phase transition driven by the Higgs field. This mechanism does not work in the SM, but can be viable if there are new particles near the weak scale that interact significantly with the Higgs boson. These particles will generally modify the decay rates of the Higgs, and may even lead to exotic new decay channels. The third focus of this proposal is the study of mechanisms of electroweak baryogenesis and their connection to searches at the LHC and precision experiments.