Abstract
We summarize the present state of research on the darkon fluid as a model for the dark sector of the Universe. Nonrelativistic massless particles are introduced as a realization of the Galilei group in an enlarged phase space. The additional degrees of freedom allow for a nonstandard, minimal coupling to gravity respecting Einstein’s equivalence principle. Extended to a self-gravitating fluid the Poisson equation for the gravitational potential contains a dynamically generated effective gravitational mass density of either sign. The equations of motion (EOMs) contain no free parameters and are invariant w.r.t. Milne gauge transformations. Fixing the gauge eliminates the unphysical degrees of freedom. The resulting Lagrangian possesses no free particle limit. The particles it describes, darkons, exist only as fluid particles of a self-gravitating fluid. This darkon fluid realizes the zero-mass Galilean algebra extended by dilations with dynamical exponent z = 5/3 . We reduce the EOMs to Friedmann-like equations and derive conserved quantities and a unique Hamiltonian dynamics by implementing dilation symmetry. By the Casimir of the Poisson-bracket (PB)-algebra we foliate the phase space and construct a Lagrangian in reduced phase space. We solve the Friedmann-like equations with the transition redshift and the value of the Casimir as integration constants. We obtain a deceleration phase for the early Universe and an acceleration phase for the late Universe in agreement with observations. Steady state equations in the spherically symmetric case may model a galactic halo. Numerical solutions of a nonlinear differential equation for the gravitational potential lead to predictions for the dark matter (DM) part of the rotation curves (RCs) of galaxies in qualitative agreement with observational data. We also present a general covariant generalization of the model.
Highlights
Understanding the dark sector of the Universe is one of the greatest challenges of today’s theoretical physics
In this paper we review some ongoing research on a model which is a first building block for a new theory describing the dark sector of the Universe
We demonstrate that our model gives a proper description of the late time cosmic acceleration but it predicts galactic halos and, qualitatively correct, the corresponding flat rotation curves (RCs)
Summary
Understanding the dark sector of the Universe is one of the greatest challenges of today’s theoretical physics. We demonstrate that our model gives a proper description of the late time cosmic acceleration but it predicts galactic halos and, qualitatively correct, the corresponding flat rotation curves (RCs) To do this we derive for the spherically symmetric steady state case a nonlinear ordinary differential equation for the gravitational potential which is solved numerically. Galactic rotation curves) serves only as an illustration that it might be meaningful to develop the present model to a proper theory of gravitation for the dark sector of the Universe For this reason we do not produce any least square fits for the undetermined integration constants appearing in the cosmological context. We close with some conclusions and give an outlook for future work
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