  We consider the theory of a light conformally coupled scalar field, i.e., one
that is coupled directly to the Ricci scalar of the gravitational sector. This
theory can be written equivalently as one of a light scalar that is coupled to
the Standard Model of particle physics with a particular combination of
Higgs-portal couplings. When the conformal coupling function contains terms
that are linear and quadratic in the conformally coupled scalar, we find that
the effective mass of the light propagating mode and its coupling to matter
fields, obtained after expanding around a minimum of the classical potential,
depend on the energy density of the background environment. This is despite the
absence of non-linear terms in the original equation of motion for the light
conformally coupled field. Instead, we find that the non-linearities of the
prototype Higgs potential are communicated to the light mode. In this way, we
present a novel realisation of screening mechanisms, in which light degrees of
freedom coupled to the Standard Model are able to avoid experimental
constraints through environmental and thin-shell effects.
