  The weak-gravity bound has been discovered in several asymptotically safe
gravity-matter systems. It limits the strength of gravitational fluctuations
that are compatible with an ultraviolet-complete matter sector, and results
from the collision of two partial fixed points of the matter system as a
function of the strength of the gravitational interactions. In this paper, we
will investigate this mechanism in detail for a shift-symmetric scalar field.
First, we will study the fixed point structure of the scalar system without
gravity. We find indications that the Gaussian fixed point is the only viable
fixed point, suggesting that a weak-gravity bound resulting from the collision
of two partial fixed points is a truncation artefact. We will then couple the
scalar system to gravity and perform different expansions to track the Gaussian
fixed point as gravitational fluctuations become stronger. We also introduce a
new notion of the weak-gravity bound that is based on the number of relevant
operators.
