Investigating dark matter substructure with pulsar timing: II. Improved limits on small-scale cosmology

TL;DR

This paper uses pulsar timing observations to set improved, particle-independent constraints on small-scale dark matter structures like UCMHs, informing early universe conditions and structure formation theories.

Contribution

It provides the strongest constraints to date on UCMH abundance from pulsar timing, surpassing previous limits from dark matter annihilation, and links these to early universe scenarios.

Findings

Limits on UCMH abundance are the strongest to date at some scales.

Constraints are independent of dark matter particle properties.

Results inform models of primordial power, non-Gaussianity, and cosmic strings.

Abstract

Ultracompact Minihalos (UCMHs) have been proposed as a type of dark matter sub-structure seeded by large-amplitude primordial perturbations and topological defects. UCMHs are expected to survive to the present era, allowing constraints to be placed on their cosmic abundance using observations within our own Galaxy. Constraints on their number density can be linked to conditions in the early universe that impact structure formation, such as increased primordial power on small scales, generic weak non-Gaussianity, and the presence of cosmic strings. We use new constraints on the abundance of UCMHs from pulsar timing to place generalised limits on the parameters of each of these cosmological scenarios. At some scales, the limits are the strongest to date, exceeding those from dark matter annihilation. Our new limits have the added advantage of being independent of the particle nature of dark matter, as they are based only on gravitational effects.