In string theory, there are no fundamental constants. Instead, all coupling constants are given by vacuum expectation values of scalar fields known as moduli fields. In top-down constructions of low-energy effective theories from string theory, the fundamental constants should in principle be derived (through a specific compactification scenario) from such vevs at a high scale, but there are many obstacles and difficulties involved in constructing the Standard Model (or extensions thereof) from string theory. In this talk, I instead consider the idea of couplings set by scalar fields in bottom-up constructions, where the low-energy theory is constructed at lower scales as an effective field theory with a cutoff scale. When fundamental constants are set by scalar fields, they are constant at low enough energies, when the field is stuck at the bottom of the potential minimum. If the field gets excited the constants can change, and models of this kind are therefore models for varying coupling constants. In a previous paper [arXiv:1601.00624] we considered the LHC phenomenology of the scalar field that lets the electromagnetic coupling vary in this way. I will discuss a generalization and extension where we let the three gauge couplings of the Standard Model gauge group as well as the Yukawa couplings of the fermions be controlled by scalar fields, and I will present some collider signatures of this model.

This talk is based on U. Danielsson, R. Enberg, G. Ingelman, T. Mandal, arXiv:1601.00624, and work in progress.