Gamma-rays from ultracompact minihalos: potential constraints on the primordial curvature perturbation

Abstract

Ultracompact minihalos (UCMHs) are dense dark matter structures which can form from large density perturbations shortly after matter-radiation equality. If dark matter is in the form of Weakly Interacting Massive Particles (WIMPs), then UCMHs may be detected via their gamma-ray emission. We investigate how the {\em{Fermi}} satellite could constrain the abundance of UCMHs and place limits on the power spectrum of the primordial curvature perturbation. Detection by {\em Fermi} would put a lower limit on the UCMH halo fraction. The smallest detectable halo fraction, $f_{\mathrm{UCMH}}\gtrsim 10^{-7}$, is for $M_{\mathrm{UCMH}}\sim 10^3{M}_{\odot }$. If gamma-ray emission from UCMHs is not detected, an upper limit can be placed on the halo fraction. The bound is tightest, $f_{\mathrm{UCMH}}\lesssim 10^{-5}$, for $M_{\mathrm{UCMH}}\sim 10^5{M}_{\odot }$. The resulting upper limit on the power spectrum of the primordial curvature perturbation in the event of non-detection is in the range ${\mathcal{P}}_{\mathcal{R}}\lesssim 10^{-6.5}-10^{-6}$ on scales $k\sim 10^1-10^6{\mathrm{Mpc}}^{-1}$. This is substantially tighter than the existing constraints from primordial black hole formation on these scales, however it assumes that dark matter is in the form of WIMPs and UCMHs are not disrupted during the formation of the Milky Way halo.

5 pages, 2 figures, version to appear in Phys. Rev. D, minor changes

References in corpus (2)

• Generalised constraints on the curvature perturbation from primordial black holes
• Superdense cosmological dark matter clumps

Cited by in corpus (12)

• Primordial Black Holes as Dark Matter
• Testing scenarios of primordial black holes being the seeds of supermassive black holes by ultracompact minihalos and CMB $\mu$-distortions
• Observable Spectra of Induced Gravitational Waves from Inflation
• Small-scale clumps of dark matter
• Non-perturbative approach for curvature perturbations in stochastic-$\delta N$ formalism
• 3D simulations with boosted primordial power spectra and ultracompact minihalos
• Predicting the density profiles of the first halos
• Point Sources from Dissipative Dark Matter
• Constraints on the small scale curvature perturbation using Planck-2015 data
• Constraints on the primordial power spectrum of small scales using the neutrino signals from the dark matter decay
• Constraints on the ultracompact minihalos using neutrino signals from the gravitino dark matter decay
• Constraints on small-scale cosmological perturbations from gamma-ray searches for dark matter