  After the possible discovery of new heavy particles at the LHC, it will be
crucial to determine the properties and the underlying physics of the new
states. In this work, we focus on scalar trilinear couplings, employing as an
example the case of the trilinear coupling of scalar partners of the top quark
to the Higgs boson. We discuss possible strategies for experimentally
determining the scalar top (stop) trilinear coupling parameter, which controls
the stop--stop--Higgs interaction, and we demonstrate the impact of different
renormalisation prescriptions for this parameter. We find that the best
prospects for determining the stop trilinear coupling arise from its quantum
effects entering the model prediction for the mass of the SM-like Higgs boson
in comparison to the measured value. We point out that the prediction for the
Higgs-boson mass has a high sensitivity to the stop trilinear coupling even for
heavy masses of the non-standard particles. Regarding the renormalisation of
the stop trilinear coupling we identify a renormalisation scheme that is
preferred in view of the present level of accuracy and we clarify the source of
potentially large logarithms that cannot be resummed with standard
renormalisation group methods.
