Probing small-scale power spectra with pulsar timing arrays

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.

Dark Unification: a UV-complete Theory of Asymmetric Dark Matter

“…This implies a period of Early Matter Domination, where metric perturbations on small scales can enter the horizon and grow. Scales that were inside the horizon during this period of EMD, can give rise to enhanced matter power spectrum on small scales, corresponding to subhalos of mass 10 −15 −10 −11 M for T RH = 1 GeV and 10 −9 −10 −4 M for T RH = 1 MeV [67].…”

Dark freeze-out cogenesis

“…As a result, we generally expect a peak in density perturbations between the two scales, leading to a potentially observable enhancement in the local subhalo abundance. The ensuing altered predictions of the ionization history as well as of the halo-mass function in the late Universe can be probed with various strategies [81,[86][87][88][89][90]. In particular, future Pulsar Timing Arrays (PTA) will be able to constrain the abundance of local subhalos down to a halo mass of 10 −10 M , and thus have the sensitivity to probe effects on primordial perturbations at co-moving scales as small as 10 −7 Mpc [89,91].…”

“…The ensuing altered predictions of the ionization history as well as of the halo-mass function in the late Universe can be probed with various strategies [81,[86][87][88][89][90]. In particular, future Pulsar Timing Arrays (PTA) will be able to constrain the abundance of local subhalos down to a halo mass of 10 −10 M , and thus have the sensitivity to probe effects on primordial perturbations at co-moving scales as small as 10 −7 Mpc [89,91]. Such a scale corresponds to τ ∼ 10 −6 s, or, conversely, a reheating temperature of T end ∼ 300 MeV following the end of the EMD era.…”

Dark Freeze-out Cogenesis

“…As a result, we generally expect a peak in density perturbations between the two scales, leading to a potentially observable enhancement in the local subhalo abundance. The ensuing altered predictions of the ionization history as well as of the halo-mass function in the late Universe can be probed with various strategies [80,[85][86][87][88][89]. In particular, future Pulsar Timing Arrays (PTA) will be able to constrain the abundance of local subhalos down to a halo mass of 10 −10 M , and thus have the sensitivity to probe effects on primordial perturbations at co-moving scales as small as 10 −7 Mpc [88,90].…”

“…The ensuing altered predictions of the ionization history as well as of the halo-mass function in the late Universe can be probed with various strategies [80,[85][86][87][88][89]. In particular, future Pulsar Timing Arrays (PTA) will be able to constrain the abundance of local subhalos down to a halo mass of 10 −10 M , and thus have the sensitivity to probe effects on primordial perturbations at co-moving scales as small as 10 −7 Mpc [88,90]. Such a scale corresponds to τ ∼ 10 −6 s, or, conversely, a reheating temperature of T end ∼ 300 MeV following the end of the EMD era.…”