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 (M OND). I first write down a two-field Langrangian-based theory of MOND (nonr elativistic) that embodies several assumptions, such as constancy of the MO ND acceleration parameter, association of a MOND force with peculiar accele rations 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 th is theory, the equation for the evolution of spherically symmetric overdens ities is nonlinear and implies very rapid growth even in a low-density back ground, particularly at the epoch when the putative cosmological constant b egins to dominate the Hubble expansion. Small comoving scales enter the MON D regime earlier than larger scales and therefore evolve to large overdensi ties sooner. Taking the initial COBE-normalized power spectrum provided by Seljak and Zeldar-riaga's CMBFAST, I find that the final power spectrum res embles that of the standard Lambda CDM universe and thus retains the empiri cal successes of that model.