Cristin Chall (University of South Carolina)
The Standard Model (SM) is one of our most well tested and highly confirmed theories. However, physicists, perceiving flaws in the SM, have been building models describing physics that goes beyond it (BSM). Many of these models describe alternatives to the Higgs mechanism, the SM explanation for electroweak symmetry breaking (EWSB). So far, no BSM model has been empirically successful; meanwhile, the Higgs particle discovered in 2012 has exhibited exactly the properties predicted by the SM. Despite this, many BSM models have remained popular, even years after this SM-like Higgs boson has been found. This is surprising, since it appears to y in the face of conventional understandings of scientific practice to have competing models interacting in a complex dynamics even though none of them have achieved empirical success and all of them are faced with a predictively superior alternative. The question becomes: How do we rationally explain physicists' continued work on models that, though not entirely excluded, are increasingly experimentally disfavoured?
I will argue that the best framework for explaining these complex model dynamics is the notion of scientific research programmes, as described by Lakatos (1978). To apply this framework, however, I need to modify it to accommodate the collections of models which share the same core theoretical commitments, since Lakatos dismisses models to the periphery of research programmes. These collections of models, which I call `model-groups', behave as full-edged research programmes, supplementing the series of theories that originally defined research programmes. By allowing the individual models to be replaced in the face of unfavourable empirical results, the hard core of a model-group is preserved. The practical benefit of applying this framework is that it explains the model dynamics: physicists continue to formulate and test new models based on the central tenets of a model-group, which provide stability and avenues for making progress, and rationally continue giving credence to BSM models lacking the empirical support enjoyed by the SM account of EWSB.
To demonstrate the model dynamics detailed by the Lakatosian framework, I will use the Composite Higgs model-group as an example. Composite Higgs models provide several benefits over the SM account, since many have a dark matter candidate, or accommodate naturalness. However, the measured properties of the Higgs boson give every indication that it is not a composite particle. I trace the changing strategies used in this model-group in order to demonstrate the explanatory power of Lakatosian research programmes applied in this new arena. Thus, I show that Lakatos, suitably modified, provides the best avenue for philosophers to describe the model dynamics in particle physics, a previously under-represented element of the philosophical literature on modelling.
