3D simulations with boosted primordial power spectra and ultracompact minihalos

Abstract

We perform three-dimensional simulations of structure formation in the early Universe, when boosting the primordial power spectrum on approximately kpc scales. We demonstrate that our simulations are capable of producing power-law profiles close to the steep $\rho \propto r^{-9/4}$ halo profiles that are commonly assumed to be a good approximation to ultracompact minihalos (UCMHs). However, we show that for more realistic initial conditions in which halos are neither perfectly symmetric nor isolated, the steep power-law profile is disrupted and we find that the Navarro-Frenk-White profile is a better fit to most halos. In the presence of background fluctuations even extreme, nearly spherical initial conditions do not remain exceptional. Nonetheless, boosting the amplitude of initial fluctuations causes all structures to form earlier and thus at larger densities. With sufficiently large amplitude of fluctuations we find that values for the concentration of typical halos in our simulations can become very large. However, despite the signal coming from dark matter annihilation inside the cores of these halos being enhanced, it is still orders-of-magnitude smaller compared to the usually assumed UCMH profile. The upper bound on the primordial power spectrum from the non-observation of UCMHs should therefore be re-evaluated.

19 pages, 20 figures. v2: Minor changes to match the published version

References in corpus (8)

• Gamma Ray Signals from Dark Matter: Concepts, Status and Prospects
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• Primordial black holes from inflaton and spectator field perturbations in a matter-dominated era
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• Self-Similar Solutions of Triaxial Dark Matter Halos
• Primordial Black Hole as a Source of the Boost Factor
• Constraints on the primordial power spectrum of small scales using the neutrino signals from the dark matter decay

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• Dark Matter Microhalos in the Solar Neighborhood: Pulsar Timing Signatures of Early Matter Domination
• Smooth vs instant inflationary transitions: steepest growth re-examined and primordial black holes
• The DAMPE excess and gamma-ray constraints
• Constraints on small-scale primordial density fluctuation from cosmic microwave background through dark matter annihilation
• Minihalos as probes of the inflationary spectrum: accurate boost factor calculation and new CMB constraints
• How an era of kination impacts substructure and the dark matter annihilation rate
• Toward More Realistic Mass Functions For Ultradense Dark Matter Halos
• Astrophysical Searches and Constraints on Ultralight Bosonic Dark Matter
• Structure Formation with Warm White Noise: Effects of Finite Number Density and Velocity Dispersion in Particle and Wave Dark Matter
• Enhanced Small-Scale Structure in the Cosmic Dark Ages
• Evidence for axion miniclusters with an increased central density
• Ultradense Dark Matter Halos with Poisson Noise from Stellar-Mass Primordial Black Holes
• Updated constraints on the primordial power spectrum at sub-Mpc scales
• Impact of a Rapid Diluted Energy Density on the halo mass function