The Standard Model (SM) of particle physics explains very precisely the interactions of the subatomic particles which constitute all of the matter we see. There are some hints, however, that the SM is incomplete – that we need physics beyond the Standard Model (BSM). For instance, the SM cannot explain dark matter, a mysterious form of matter which is over 5 times more abundant than the matter we know. There are many proposed extensions of the SM that contain new particles which could take the role of dark matter, ranging from supersymmetry to theories containing exotic particles such as axions. When we see data that hints at BSM physics, whether from astrophysical measurements (as is the case for dark matter) or data taken at the Large Hadron Collider (LHC), it is important to come up with BSM theories that can explain the data and carefully examine the implications of these theories for current and future experiments.
Exploring New Physics
Theories of BSM physics include new particles and interactions which can have significant effects on physical quantities measured by current experiments. In order to understand the allowed values of parameters of the new theory, such as the masses of new particles and strengths of new couplings, we need to determine how experimental measurements can constrain the new parameter space. One powerful method of exploring parameter spaces employed by the SLAC theory group is to sample the full space by “throwing darts” – randomly generating values of every parameter to specify a point in the overall space, and then calculating the various constraining quantities, which come from experiment, for those parameter values. If a point is allowed by all present measurements, then it is considered to be a viable new physical model. An example of such a sampling in the Left-Right Symmetric Model is shown in the first figure, with three different physical observables plotted against each other. By generating a large number of viable models, we can get a better idea of how to best search for them. The idea of using multiple measurable quantities to cover as much of the parameter space as possible is known as complementarity, and studies of complementarity in BSM physics are important for informing the design of new experiments. The second figure shows the complementarity of three types of dark matter searches – direct detection, indirect detection, and collider production – for a class of supersymmetric models. Phenomenologists in the SLAC theory group spend their time thinking about how to cover as much parameter space as possible and identifying regions where current experiments are not sensitive in order to better explore physics beyond the Standard Model.