Theoretical Physics Colloquium: Eran Palti

Abstract: Physics is built on effective descriptions that are valid at certain energy scales but break down at some sufficiently high energies. In principle, the effective description should be reached by integrating over the high-energy scales in the path integral. In practice, this is almost always too hard, and instead we construct the description in some other ways. In this talk, I will consider what happens when we actually do perform this integration, scale-by-scale, to determine low-energy effective descriptions of string theory. I will argue that this yields surprises when compared to more traditional approaches to determining the effective theory. In particular, that it implies certain relations between the low-energy parameters of the theory and the spectrum of high-energy states. These relations match certain observed universal features of low-energy effective theories in string theory that were discovered as part of the Swampland program, a research field aiming to determine universal model-independent physics of string theory. I will therefore propose that Swampland features, which have seen much interest in the theory, phenomenology and cosmology communities, arise naturally and explicitly, and can be derived microscopically, in a path-integral scale-by-scale approach to string theory.