  We minimally extend the SM with a Z$_2$ symmetric potential containing a
single scalar field, serving as our inflaton with a quartic self-coupling. In
the model we have symmetry breaking in both sectors, and with the addition of
an inflaton-Higgs portal, the Universe is able to efficiently reheat via 2-2
inflaton-Higgs scattering. Assuming that the Universe with a positive
cosmological constant should be metastable, only one particular symmetry
breaking pattern in the vacuum is possible, without the need to finely-tune the
Higgs' quartic self-coupling. Inflaton with masses in the range $O(10^{-3})\leq
m_{\chi}\leq m_{h}$ and mixing angles that span
$\theta_{m}^{2}=O(10^{-11}-10^{-2})$ evade all current cosmological,
experimental and stability constraints required for a metastable EW vacuum.
Upgraded particle physics experiments may be able to probe the parameter space
with $\theta_{m}^{2}\geq O(10^{-4})$, where we would observe trilinear Higgs
couplings suppressed by up to $2\%$ compared to the SM value. However to access
the parameter space of very weakly-coupled inflaton, we rely on the proposals
to build experiments that target the hidden sector.
