Gravitational fifth forces as a probe of symmetry breaking in the Standard Model

by Dr Pete Millington (Nottingham)

Monday 3 Sept 2018, 14:00 → 15:00 Europe/Berlin

Seminarraum3344 (Physik-Department)

The simplest modifications of general relativity often involve coupling additional scalar fields to the scalar curvature, resulting in conformally-coupled scalar-tensor theories.  Indeed, any interacting scalar fields, including the Higgs field of the Standard Model (SM), naturally obtain such non-minimal couplings through their renormalization-group evolution.  If any of the non-minimally-coupled fields are light, they can mediate long-range fifth forces.  One must then fine-tune couplings or introduce screening mechanisms in order to evade local tests of gravity.  In this talk, we focus on how fifth-force phenomenology depends on the origin of scale breaking and, in particular, on the structure of the SM and its extensions.  In doing so, we will argue that conformally-coupled scalar-tensor theories are nothing other than Higgs-portal theories.  As a result, if one assumes that light conformally-coupled fields exist in nature, Solar System tests of gravity can, quite remarkably, tell us about the origin of scale symmetry breaking in the SM Higgs sector.  Our results illustrate the phenomenological importance (both for cosmology and high-energy physics) of considering modified theories of gravity also as concrete extensions of the SM.