January 16: “Apparent fine-tunings from broken spacetime symmetries” by Alberto Nicolis

Abstract: I will exhibit a class of effective field theories that have hierarchically small Wilson coefficients for operators that are not protected by symmetries but are not finely tuned. These theories possess bounded target spaces and vacua that break space-time symmetries. I will give a physical interpretation of these theories as generalized solids with open boundary conditions. I will show that these theories can realize unusual RG flows where higher dimensional (seemingly irrelevant) operators become relevant even at weak coupling. Finally, I will present an example of a field theory whose vacuum energy relaxes to a hierarchically small value compared to the UV cut-off.