Curvaton hypothesis and the $\eta$ problem of quintessential inflation, with and without branes

It is argued why, contrary to expectations, steep brane-inflation cannot really help in overcoming the $\eta$ problem of quintessential inflation model building. In contrast it is shown that the problem is substantially ameliorated under the curvaton hypothesis. This is quantified by considering possible modular quintessential inflationary models in the context of both standard and brane cosmology.