Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2022-2023)

The first revelation of new physics, outside of the standard model of elementary particles, could come from any of a great range of different kinds of experimental searches. These include creation of new kinds of particles in the laboratory, such as the Large Hadron Collider (LHC), by high-energy particle collisions, as well as astrophysical searches for such new particles coming from the cosmos. This proposal aims to synthesize data coming from a wide range of experiments and interpret it in terms of possible new models of particle physics, to maximize our chances of discovery.

In particular, we will investigate possible new effects of the dark matter of the universe, known to be present but as yet unidentified. For example a small dark matter component with very strong self-interactions might be able to shed light on the conundrum of early formation of supermassive black holes, or the unknown origin of ultra-diffuse galaxies. Decaying dark matter with a very long lifetime could explain the highest energy neutrinos measured by the IceCube observatory in Antarctica. Dark matter with interactions that do not respect the symmetry between particles and antiparticles could help to explain the preponderance of matter over antimatter (known as the baryon asymmetry) in the universe. Such new interactions should be within the discovery reach of LHC.

If the LHC does not discover new particles in the next few years, we will be forced to rely upon less direct hints of possible new physics. One of these is the peculiar observation that the potential of the Higgs boson is very close to the edge of stability, when extrapolated to very high energies. This can have profound consequences in the early universe, where we believe that a rapid period of inflationary expansion preceded the big bang. Such an instability has been shown to lead to a subsequent universe very unlike our own, hence the Higgs potential should remain stable up to high energies. Whether it does so depends upon the interactions of the Higgs boson with possible new particles beyond the standard model, including dark matter. We propose to search for links between the Higgs boson instability and two other problems of the standard model of particle physics: why the Higgs mass and the vacuum energy of the universe are so far below the high scale where they should naturally be, known as the Planck scale, that governs quantum gravity.