The Formation of Cosmic Structure with Modified Newtonian Dynamics

I consider the growth of inhomogeneities in a low-density baryonic, vacuumenergy-dominated universe in the context of modified Newtonian dynamics (MOND).I first write down a two-field Langrangian-based theory of MOND(non-relativistic), which embodies several assumptions such as constancy of theMOND acceleration parameter, association of a MOND force with peculiaraccelerations only, and the deceleration of the Hubble flow as a backgroundfield which influences the dynamics of a finite size region. In the context ofthis theory, the equation for the evolution of spherically symmetricover-densities is non-linear and implies very rapid growth even in alow-density background, particularly at the epoch when the putativecosmological constant begins to dominate the Hubble expansion. Small comovingscales enter the MOND regime earlier than larger scales and therefore evolve tolarge over-densities sooner. Taking the initial COBE-normalized power spectrumprovided by CMBFAST (Seljak & Zeldarriaga 1996), I find that the finalpower-spectrum resembles that of the standard LCDM universe and thus retainsthe empirical successes of that model.Comment: revised version includes a Lagrangian-based, non-relativistic theory of modified dynamics; conclusions are unchanged; accepted for publication (ApJ