Constraints on MeV dark matter and primordial black holes: Inverse Compton signals at the SKA

Abstract

We investigate the possibilities for probing MeV dark matter (DM) particles and primordial black holes (PBHs) (for masses ∼ 10 15 -10 17 g) at the upcoming radio telescope SKA, using photon signals from the Inverse Compton (IC) effect within a galactic halo. Pair-annihilation or decay of MeV DM particles (into e + e − pairs) or Hawking radiation from a population of PBHs generates mildly relativistic e ± which can lead to radio signals through the IC scattering on low energy cosmic microwave background (CMB) photons. We study the ability of SKA to detect such signals coming from nearby ultra-faint dwarf galaxies Segue I and Ursa Major II as well as the globular cluster ω-cen and the Coma cluster. We find that with ∼ 100 hours of observation, the SKA improves the Planck constraints on the DM annihilation/decay rate and the PBH abundance for masses in the range ∼ 1 to few tens of MeV and above 10 15 to 10 17 g, respectively. Importantly, the SKA limits are independent of the assumed magnetic fields within the galaxies. Previously allowed regions of diffusion parameters of MeV electrons inside a dwarf galaxy that give rise to observable signals at the SKA are also excluded.

Baryogenesis from ultra-slow-roll inflation

“…Nevertheless, despite the fact that the USR transition provides a quantitative connection between baryon and PBH densities with a viable answer to the cosmic coincidence problem independent of the statistical uncertainties, the existing fine-tuning problem for the inflaton potential to realize PBH dark matter inevitably enters the story of cosmology. On the other hand, the asteroidmass window for PBH dark matter, one of the fundamental assumption in this work, could be tested by near future astrophysical or gravitational-wave experiments [103][104][105][106][107][108][109][110][111][112][113][114][115].…”

Universal profiles for radio searches of dark matter in dwarf galaxies

“…3 the ranges of validity in the (τ 0 , E) plane of the A, B and C approximations. Specifically, we compute at every point the quantity f 2 = X τ 0 4 ,E / Xτ0,E , i. e. the ratio of the 2th-to the 1st-order spectral function (see (36)) and we then set threshold values for every approximation: f 2 > 1/2 for RA, 1 4 × 0.9 < f 2 < 1 4 × 1.1 for RC and f 2 < 20% in the RB case. These conditions are constructed by noting that in the pure RA situation f 2 → 1, while f 2 → 1/2 2 = 1/4 if the RC formula were exact.…”

“…Armed with the numerical strategies discussed in previous sections, we can test the performance of our approximated formula (29) across the different characteristic regimes of the problem. Specifically, as mentioned above, we have devised a series of methods that are very efficient in evaluating the (exact) formula (36) which will allow us to test the accuracy of the RA-RC formulas.…”

“…5 shows the results of our comparisons. In all cases, we include the exact (36) and the approximated (29) (with ( 33)-( 35)) computations of the emissivity for several halo models and within the aforementioned benchmark parameter sets. In order to quantify the morphological resemblance between the different predictions, we also show their corresponding HFRs (vertical lines).…”

“…[29] some of these methods were used in putting constraints on the DM annihilation cross section using observations of the Canes Venatici I dwarf spheroidal (dSph) galaxy. Our methods are transferable to modelling the inverse Compton scattering X-ray (soft gamma-ray) signal in dSphs with direct impact on indirect detection of WIMPs, decaying DM and even primordial black holes (see e. g. [36]). In return for the comprehensive attention we paid on all details, we also partly correct results that have been employed in previous works.…”