Basically, the concept is that the Pauli exclusion principle applies equally to arbitrarily long wavelength fermions, even those whose wavelength scales with the Hubble length. This results in those arbitrarily long wavelength fermions being frozen into the horizon. This "freezing" is due to the recession rate of each side of the horizon being the speed of light i.e., a crest or trough in any wavefunction on one side of the horizon cannot catch up with its counterpart on the other side of the horizon effectively freezing them in place. To the extent that there are effectively indistinguishable primordial, relic or modern fermions present which are frozen into this horizon, the Pauli exclusion principle will push these apart to maintain conservation of fermion number. This is the same process which creates valence and conduction bands in periodic/crystalline atomic lattices and prevents materials from overlapping when pushed together (the valence electrons cannot overlap giving rise to the equal and opposite force). This will effectively provide a standard model mechanistic force pushing the horizon out further to the extent that these frozen overlapping fermions are coupled to the horizon. This mechanistically will provide a dark energy like force contributing to universal expansion initiated at the big bang with inflation. More details are provided in the online version of the published paper.
Assuming Planck time and length scales at the moment of creation in a "pure" singularity consistent with classical general relativity, the assumption of existence of all physical laws in the standard model allows a mechanistic model for inflation. Specifically, with all existent and virtual fermions being present at the initial moment of existence, these will submit to the Pauli exclusion principle and transition through quantum tunneling to spatially distinct (minimally orthogonal) states. If this occurs in a unit of Planck time, the effective velocity this tunneling induced is many orders of magnitude greater than the speed of light (~1E20c) of each particle away from its nearest neighbors. With momentum conservation being another standard model law applicable to creation, the outward expansion effect is then a clear result comparable to the current inflation model but not requiring any new physics such as the inflaton or string theory constructs. Further details can be found in the online version of the published paper linked below.
13. A Standard Model Approach to Dark Energy and Inflation, Robert Bruce Hayes, North Carolina State University, Nuclear Engineering Department, June 26, 2017, pp 14850-14859http://journalofcosmology.com/JOC26/Hayes.pdf