Abstract
Models of Dark Matter (DM) can leave unique imprints on the Universe’s small scale structure by boosting density perturbations on small scales. We study the capability of Pulsar Timing Arrays to search for, and constrain, subhalos from such models. The models of DM we consider are ordinary adiabatic perturbations in ΛCDM, QCD axion miniclusters, models with early matter domination, and vector DM produced during inflation. We show that ΛCDM, largely due to tidal stripping effects in the Milky Way, is out of reach for PTAs. Axion miniclusters may be within reach, although this depends crucially on whether the axion relic density is dominated by the misalignment or string contribution. Models where there is matter domination with a reheat temperature below 1 GeV may be observed with future PTAs. Lastly, vector DM produced during inflation can be detected if it is lighter than 10−16 GeV. We also make publicly available a Python Monte Carlo tool for generating the PTA time delay signal from any model of DM substructure.
Highlights
ΛCDM: a nearly scale invariant spectrum of adiabatic perturbations is produced at the end of infaltion [1, 2]
Vector Dark Matter (DM) Produced During Inflation: if the DM is a massive spin-1 particle, the longitudinal modes produced at the end of inflation can peak the power spectrum at small scales, with the location of the peak determined by the DM mass [7]
We have studied the detectability in Pulsar Timing Arrays of a variety of well motivated DM models of substructure including: standard ΛCDM, axion models where the PQ symmetry breaks after inflation, early matter domination, and vector DM
Summary
We begin with a discussion of the signal induced in PTAs by DM subhalos, how we generate this signal with the Monte Carlo, and the signal-to-noise ratio (SNR) of such a signal. [17, 18] and we review them here for completeness. Many of the formulae presented here were previously derived in refs. Both the Doppler effect (acceleration induced by a DM subhalo of either the Earth or a pulsar (called the Earth or pulsar terms, respectively)), and Shapiro effect (a change in the light arrival time due to the DM subhalo gravitational potential) were considered. We will only consider signals from the Doppler effect, which is dominant over the Shapiro effect for subhalos with mass below M 10−3M for any concentration parameter We will only consider signals from the Doppler effect, which is dominant over the Shapiro effect for subhalos with mass below M 10−3M for any concentration parameter (see ref. [18])
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