Clues from string theory about UV/IR mixing and UV-completion

by Steven Abel (Durham)

Thursday 10 Apr 2025, 16:15 → 18:15 Europe/Berlin

There are several mysteries, such as the hierarchy problem, that are thought to be associated with our incomplete understanding of quantum gravity. One interesting viewpoint is that their resolution is associated with a high degree of UV/IR mixing in the fundamental theory that we cannot see at the level of the effective theory. There are many questions that arise in UV/IR-mixed theories, most notably how can one even define an energy scale in a UV/IR mixed theory and how can one extract sensible effective field theory behaviour? In this talk I will show that string theory is an important guide as to how all these issues are resolved. Taking a generic approach, I will highlight the special properties of string theory that allow it to have a sensible low energy effective description. We will see that there is a way to recast these constraints on the theory in a particle physics manner as new super-trace conditions which must be obeyed even in a non-supersymmetric theory, and which must be exact. These super trace constraints lead to new non-renormalisation theorems which arise from UV/IR mixing, and which lead to a number of surprising phenomenological consequences. Chief among them is the fact that certain physical quantities within such theories cannot exhibit logarithmic or power-law running. This cessation of running occurs as the result of the UV/IR mixing inherent in the theory, reinforcing the notion that UV/IR mixing may play a vital role in resolving hierarchy problems without supersymmetry. The talk will be pedagogical.