Hall 123

An Ode To Action

Dr. Subhroneel Chakrabarti

Institute of Physics of the Czech Academy of Sciences

The action principle has been a cornerstone in the evolution of
theoretical physics over the last century, guiding the development of
myriad theoretical frameworks. However, recent research has ventured into a domain "beyond the action principle," probing quantum field theories (QFTs) independent of conventional action-based approaches. In this talk, we will
highlight two specific instances where the absence of action principles was
widely presupposed, yet subsequent careful investigations revealed the
emergence of an action.

The first instance involves the famous case of chiral bosons, for which a
novel action-based formulation has been recently identified, contingent
upon an expanded notion of constructing an action. The second pertains to the innovative third-way consistent gauge theories, which describe self-interacting p-form fields without seemingly relying on an action
principle. I will show how our recent examination of these third-way gauge
theories brings us back to an action-based description. I will conclude
with a discussion of the class of QFTs that genuinely elude action
principles, advocating for a deeper comprehension of the family of QFTs
that do accommodate action-based descriptions.