Speaker
Description
If string theory provides a consistent theory of everything, it should make predictions about cosmology that can be checked against observation.
In spite of this, it has proved incredibly challenging to obtain any concrete testable predictions from string theory.
In the first part of this talk I will give a broad-level overview of the 'landscape' picture of string theory and how the first semi-realistic cosmologies from string theory were proposed in this way about 25 years ago today. I will discuss how in more recent years growing cracks in these constructions have been discovered and where this leaves us today: with seemingly no good controlled models in string theory with either inflation or even a positive cosmological constant.
In the second part of the talk I will discuss the 'swampland' picture, where instead one seeks to constrain effective theories at low energies by arguing that certain EFTs cannot be consistently completed into a theory of quantum gravity. As a specific example I will discuss the 'Festina Lente' bound which constrains both cosmology and the spectrum of charged particles in a theory. I will mention some upcoming results strengthening this bound.