The formation of cosmic structure with modified Newtonian dynamics

I consider the growth of inhomogeneities in a low-density, baryonic, vacuum energy-dominated universe in the context of modified Newtonian dynamics (MOND). I first write down a two-field Langrangian-based theory of MOND (nonrelativistic) that embodies several assumptions, such as constancy of the MOND acceleration parameter, association of a MOND force with peculiar accelerations only, and the deceleration of the Hubble flow as a background field that influences the dynamics of a finite-size region. In the context of this theory, the equation for the evolution of spherically symmetric overdensities is nonlinear and implies very rapid growth even in a low-density background, particularly at the epoch when the putative cosmological constant begins to dominate the Hubble expansion. Small comoving scales enter the MOND regime earlier than larger scales and therefore evolve to large overdensities sooner. Taking the initial COBE-normalized power spectrum provided by Seljak and Zeldar-riaga's CMBFAST, I find that the final power spectrum resembles that of the standard Lambda CDM universe and thus retains the empirical successes of that model.