Search

Primordial black holes (PBHs) are hypothetical objects formed at the early epoch of the universe, which could be a type of dark matter (DM) candidate without the need for new particles. The abundance of PBH DM has been constrained strictly by many observations.In this work, with the radio observations of Fornax and Segue I, we constrain the abundance of PBH in dwarf spheroidal galaxies through the synchrotron self-Compton (SSC) effect of Hawking radiation electrons. By selecting optimal sources, we obtain the constraints on the fraction of PBH DM down to $\sim10^{-3}$ for Segue I and $\sim10^{-5}$ for Fornax at asteroidal mass. We also predict that, with 100 hours of future observation by the Square Kilometer Array, the SSC approach could place constraints comparable to the current strictest results for PBHs of $<5\times10^{15}\,{\rm g}$. Better projected constraints can be obtained by including the inverse Compton scattering on cosmic microwave background photons., Comment: 9 pages, 6 figures, accepted for publication in PRD

Dark photon is a new gauge boson beyond the Standard Model as a kind of dark matter (DM) candidate. Dark photon dark matter (DPDM) interacts with electromagnetic fields via kinetic mixing, implicating an approach to give a constraint with extragalactic very high energy (VHE) sources. In this work, we attempt to constrain the kinetic mixing from the photon-dark photon scattering process in the host galaxy of blazar, the intergalactic medium and the Milky Way. The VHE photons from a blazar would pass through a dense DM spike around the supermassive black hole where the absorption from DPDM is dramatically enhanced. The kinetic mixing is constrained to be $\epsilon \sim 10^{-7}$ at a 95$\%$ confidence level with $m_{\rm D}\sim 0.03 - 1$ eV mass range from the observations of Markarian (Mrk) 421 and Mrk 501., Comment: 16 pages, 10 figures, 3 tables

Dwarf irregular galaxies (dIrrs), as rotationally-supported systems, have more reliable J-factor measurements than dwarf spheroidal galaxies and have received attention as targets for dark matter detection in recent years. In this paper, we use 10 years of IceCube muon-track data and an unbinned maximum-likelihood-ratio method to search for neutrino signals beyond the background from the directions of 7 dIrrs, aiming to detect neutrinos produced by heavy annihilation dark matter. We do not detect any significant signal. Based on such null results, we calculate the upper limits on the velocity-averaged annihilation cross section for 1 TeV - 10 PeV dark matter. Our limits, although weaker than the strictest constraints in the literature in this mass range, are also a good complement to the existing results considering the more reliable J-factor measurements of dIrrs., Comment: 13 pages, 4 figures, accepted for publication in RAA

Electrons and positrons produced in dark matter annihilation can generate secondary emission through synchrotron and IC processes, and such secondary emission provides a possible means to detect DM particles with masses beyond the detector's energy band. The secondary emission of heavy dark matter (HDM) particles in the TeV-PeV mass range lies within the Fermi-LAT energy band. In this paper, we utilize the Fermi-LAT observations of dwarf spheroidal (dSph) galaxies to search for annihilation signals of HDM particles. We consider the propagation of $e^+/e^-$ produced by DM annihilation within the dSphs, derive the electron spectrum of the equilibrium state by solving the propagation equation, and then compute the gamma-ray signals produced by the $e^+/e^-$ population through the IC and synchrotron processes. Considering the spatial diffusion of electrons, the dSphs are modeled as extended sources in the analysis of Fermi-LAT data according to the expected spatial intensity distribution of the gamma rays. We do not detect any significant HDM signal. By assuming a magnetic field strength of $B=1\,{\rm \mu G}$ and a diffusion coefficient of $D_0 = 3\times10^{28}\,{\rm cm^{2}s^{-1}}$ of the dSphs, we place limits on the annihilation cross section for HDM particles. Our results are weaker than the previous limits given by the VERITAS and IceCube observations of dSphs, but extend the existing limits to higher DM masses. As a complement, we also search for the prompt $\gamma$-rays produced by DM annihilation and give limits on the cross section in the 10-$10^5$ GeV mass range. Consequently, in this paper we obtain the upper limits on the DM annihilation cross section for a very wide mass range from 10 GeV to 100 PeV in a unified framework of the Fermi-LAT data analysis., Comment: 11 pages, 9 figures; add the KN effect for IC and model the secondary emission around dSphs as extended

The adiabatic growth of a black hole (BH) may enhance the dark matter (DM) density surrounding it, causing a spike in the DM density profile. The spike around the supermassive BH at the center of the Milky Way may lead to a dramatic enhancement of the gamma-ray flux of DM annihilation from the galactic center (GC). In this work, we analyze the gamma-ray data of the innermost region (i.e., the inner 1$^\circ$) of the GC to search for potential line-like signals from the BH spike. Such line-like signals could be generated in the process of DM particles annihilating into double photons. We adopt the gamma-ray data from the Dark Matter Particle Explorer (DAMPE). Although the DAMPE has a much smaller effective area than the Fermi-LAT, the gamma-ray line search can benefit from its unprecedented high energy resolution. No significant line-like signals are found in our analysis. We derive upper limits on the cross section of the annihilation based on this non-detection. We find that despite the DAMPE's small effective area for photon detection, we can still place strong constraints on the cross section ($\left<\sigma v\right>\lesssim10^{-27}\,{\rm cm^3\,s^{-1}}$) in the spike scenario due to the very bright model-expected flux from the spike. Our results indicate that either DM does not annihilate primarily through the $\gamma\gamma$ channel in the mass range we considered or no sharp density spike is present at the GC., Comment: 10 pages, 7 figures

Ultracompact minihalo (UCMH) is a special type of dark matter halo with a very steep density profile which may form in the early universe seeded by an overdense region or a primordial black hole. Constraints on its abundance give valuable information on the power spectrum of primordial perturbation. In this work, we update the constraints on the UCMH abundance in the universe using the extragalactic gamma-ray background (EGB) observation. Comparing to previous works, we adopt the updated Fermi-LAT EGB measurement and derive constraints based on a full consideration of the astrophysical contributions. With these improvements, we place constraints on UCMH abundance 1-2 orders of magnitude better than previous results. With the background components considered, we can also attempt to search for possible additional components beyond the known astrophysical contributions., Comment: Title slightly changed to match the journal version, no change in the article