Balakin, Alexander B., Bochkarev, Vladimir V. and Lemos, Jose P. S. (2012), "Light propagation with nonminimal couplings in a two-component cosmic
dark fluid with an Archimedean-type force, and unlighted cosmological
epochs", PHYSICAL REVIEW D, 85, 6.
Abstract: During the evolution of the universe there are at least two epochs
during which electromagnetic waves cannot scan the universe's internal
structure to bring information to outside observers. The first epoch is
when photons are in local thermodynamic equilibrium with other
particles, and the second is when photon scattering by charged particles
is strong. One can call these two periods of cosmological time as
standard unlighted epochs. After the last scattering surface, photons
become relic photons and turn into a source of information about the
universe. Unlighted cosmic epochs can also appear when one considers
nonminimal theories, i.e., theories in which the electromagnetic field
is coupled in an intricate way with the cosmological gravitational
field. By considering a cosmological model where the dark sector, i.e.,
the dark energy and dark matter, self-interacts via an Archimedean-type
force, and taking into account a nonminimal coupling theory for the
electromagnetic field, we discuss the appearance of unlighted epochs. In
the framework of our nonminimal theory, a three-parameter nonminimal
Einstein-Maxwell model, the curvature coupling can be formulated in
terms of an effective refraction index nd(t). Then, taking advantage of
a well-known classical analogy, namely, in a medium with n(2) < 0
electromagnetic waves do not propagate and their group velocity, i.e.,
energy transfer velocity, has zero value at the boundary of the
corresponding zone, one can search for the unlighted epochs arising in
the interacting dark fluid cosmological model. We study here, both
analytically and numerically, cosmological models admitting unlighted
epochs.
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