  Cosmology is well suited to study the effects of long range interactions due
to the large densities in the early Universe. In this article, we explore how
the energy density and equation of state of a fermion system diverge from the
commonly assumed ideal gas form under the presence of scalar long range
interactions with a range much smaller than cosmological scales. In this
scenario, "small"-scale physics can impact our largest-scale observations. As a
benchmark, we apply the formalism to self-interacting neutrinos, performing an
analysis to present and future cosmological data. Our results show that the
current cosmological neutrino mass bound is fully avoided in the presence of a
long range interaction, opening the possibility for a laboratory neutrino mass
detection in the near future. We also demonstrate an interesting
complementarity between neutrino laboratory experiments and the future EUCLID
survey.
