A large change in the predicted number of small halos due to a small amplitude oscillating inflaton potential

TL;DR

Small oscillations in the inflaton potential can significantly alter the predicted number of small halos, potentially explaining the observed scarcity of dwarf galaxies and aiding reionization models.

Contribution

This paper demonstrates that minor oscillations in the inflaton potential can cause large changes in small halo predictions, a novel insight into primordial power spectrum effects.

Findings

Oscillations can suppress halo numbers by 50% in certain mass ranges.

Small potential changes can increase small halo counts by factors of 15-50.

Potential oscillations may explain dwarf galaxy scarcity and reionization issues.

Abstract

A smooth inflaton potential is generally assumed when calculating the primordial power spectrum, implicitly assuming that a very small oscillation in the inflaton potential creates a negligible change in the predicted halo mass function. We show that this is not true. We find that a small oscillating perturbation in the inflaton potential in the slow-roll regime can alter significantly the predicted number of small halos. A class of models derived from supergravity theories gives rise to inflaton potentials with a large number of steps and many transplanckian effects may generate oscillations in the primordial power spectrum. The potentials we study are the simple quadratic (chaotic inflation) potential with superimposed small oscillations for small field values. Without leaving the slow-roll regime, we find that for a wide choice of parameters, the predicted number of halos change appreciably. For the oscillations beginning in the 10^7-10^8 solar masses range, for example, we find that only a 5% change in the amplitude of the chaotic potential causes a 50% suppression of the number of halos for masses between 10^7-10^8 solar masses and an increase in the number of halos for masses <10^6 solar masses by factors ~15-50. We suggest that this might be a solution to the problem of the lack of observed dwarf galaxies in the range 10^7-10^8 solar masses. This might also be a solution to the reionization problem where a very large number of Population III stars in low mass halos are required.