Coincidences of dark energy with dark matter: Clues for a simple alternative?

A rare coincidence of scales in standard particle physics is needed to explain why L or the negative pressure of cosmological dark energy ( DE) coincides with the positive pressure P-0 of random motion of dark matter ( DM) in bright galaxies. Recently Zlosnik and coworkers proposed to modify the Einstein curvature by adding nonlinear pressure from a medium flowing with a four-velocity vector field U-mu. We propose to check whether a smooth extension of general relativity with a simple kinetic Lagrangian of U-mu can be constructed, and whether the pressure can bend spacetime sufficiently to replace the roles of DE, cold DM, and heavy neutrinos in explaining anomalous accelerations at all scales. As a specific proof of concept we find a vector-for-Lambda model (Lambda A model) and its variants. With essentially no free parameters, these appear broadly consistent with the solar system, gravitational potentials in dwarf spiral galaxies and the Bullet Cluster of galaxies, the early universe with inflation, structure formation, and big bang nucleosynthesis, and late acceleration with a 1 : 3 ratio of DM : DE.