Enhanced spectrum of primordial perturbations, galaxy formation, and small-scale structure
The standard cosmological structure formation scenario is successful on large scales. Several apparent problems affect it however at galactic scales, such as the small scale problems at low redshift and more recent issues involving early massive galaxy and black hole formation. As these arise where complex baryonic physics becomes important, this is often assumed to be behind the problems. But the same scales are also those where the primordial spectrum is relatively unconstrained, and there are several ways in which it can be modified. We focus on that arising from effects possibly associated with the crossing of high energy cutoff scale by fluctuation modes during inflation. Elementary arguments show that adiabatic evolution cannot modify the near scale invariance, we thus discuss a simple model for the contrary extreme of sudden transition. Numerical calculations and simple arguments suggest that its predictions, for parameters considered here, are more generic than may be expected, with significant modifications requiring a rapid transition. We examine the implications of such a scenario, in this simplest form of sudden jump as well as gradual variants, on the matter power spectrum and halo mass function in light of the limitations imposed by particle production. We show the resulting enhancement and oscillation in the power spectrum on currently nonlinear scales can potentially simultaneously alleviate both the apparent problem of early structure formation and, somewhat counterintuitively, problems at low redshift concerning the abundance of dwarf galaxies, including those too big to fail. We discuss consequences that can observationally constrain the scenario and its parameters, including an inflationary Hubble scale ≲10-8MPl, while touching on the possibility of simultaneous modification of power on the largest scales.
Seleim, Karim H.; El-Zant, Amr A.; and Abdel-Moneim, A. M., "Enhanced spectrum of primordial perturbations, galaxy formation, and small-scale structure" (2020). Centre for Theoretical Physics. 185.