  We study the sensitivity of LiteBIRD and CMB-S4 to the reheating temperature
and the inflaton coupling in three types of plateau-potential models of
inflation, namely mutated hilltop inflation, radion gauge inflation, and
$\alpha$-attractor T models. We first study the relations between model
parameters and CMB observables in all models analytically. We then perform
Monte Carlo Markov Chain based forecasts to quantify the information gain on
the reheating temperature, the inflaton coupling, and the scale of inflation
that can be achieved with LiteBIRD and CMB-S4. We compare the results of the
forecasts to those obtained from a recently proposed simple analytic method. We
find that both LiteBIRD and CMB-S4 can simultaneously constrain the scale of
inflation and the reheating temperature in all three types of models. They can
for the first time obtain both an upper and lower bound on the latter,
comprising the first ever measurement. In the mutated hilltop inflation and
radion gauge inflation models this can be translated into a measurement of the
inflaton coupling in parts of the parameter space. Constraining this
microphysical parameter will help to understand how these models of inflation
may be embedded into a more fundamental theory of particle physics.

High Energy Physics - Phenomenology;Cosmology and Nongalactic Astrophysics