potential energy function near "tunnel exit" from false vacuum state must have a shallow slope, otherwise particle production will be confined to the boundary of expanding true vacuum bubble, which contradicts observation (our Universe is not built of huge completely void bubbles). In other words, the quantum state should "roll to the bottom slowly". When complete, the decay of inflaton particles fills the space with hot and dense Big Bang plasma. Field quanta Just like every other quantum field, excitations of the inflaton field are expected to be quantized. The field quanta of the inflaton field are known as inflatons. Depending on the modeled potential energy density, the inflaton field's ground state might, or might not, be zero. The term inflaton follows the typical style of other quantum particles’ names – such as photon, gluon, boson, and fermion – deriving from the word inflation. The term was first used in a paper by Nanopoulos, Olive, and Srednicki (1983). The nature of the inflaton field is currently not known. One of the obstacles for narrowing its properties down is that current quantum theory is not able to correctly predict the observed vacuum energy, based on the particle content of a chosen theory (see vacuum catastrophe). Atkins (2012) suggested that it is possible that no new field is necessary – that a modified version of the Higgs field could function as an inflaton. Non-minimally coupled inflation Non-minimally coupled inflation is an inflationary model in which the constant which couples gravity to the inflaton field is not small. The coupling constant is usually represented by (letter xi), which features in the action (constructed by modifying the Einstein–Hilbert action): , with representing the strength of the interaction between and , which respectively relate to the curvature of space and the magnitude of the inflaton field. See also References Inflation (cosmology) Hypothetical particles Dark energy