EXPERIMENTALLY TESTING ASYMPTOTICALLY SAFE QUANTUM GRAVITY WITH PHOTON-PHOTON SCATTERING

Abstract

In quantum gravity research, we strive to answer the question ”What is spacetime like on very small scales?”. More precisely, this can be rephrased as ”What is the microscopic dynamics of gravity?”, ”What are the fundamental symmetries?”, ”Is spacetime continuous or somehow discrete?”, ”What is the dimensionality of spacetime on small scales?”. To answer these, each approach to quantum gravity is founded upon assumptions. Ultimately, these should be tested in experiments. Here, matter-quantum gravity interactions provide us with two possibilities: 1) consistency tests (indirect): Here we can check, whether a particular UV completion for gravity is compatible with the observed properties of the standard model of particle physics, such as the number of fermions, scalars and gauge bosons, the global symmetries, the observed mass scales, etc. 2) direct tests: Effects such as graviton-exchange in scattering processes, can be used to study the small-scale structure of spacetime. In particular, the dimensionality of spacetime on small scales can be tested at near-future experiments. For examples of the first option, where the consistency of asymptotically safe quantum gravity, as well as other models for quantum gravity, with the existence of light fermions in our universe is tested, see. Within the truncation of the full Renormalization Group (RG) flow employed in this work, asymptotic safety is compatible with fermion masses much below the Planck mass, whereas restrictions are placed on the parameter space for other quantum gravity models.