Recent TeV observations of nearby pulsars with the HAWC telescope have been interpreted as evidence that diffusion of high-energy electrons and positrons within pulsar wind nebulae is highly inefficient compared to the rest of the interstellar medium. If the diffusion coefficient well outside the nebula is close to the value inferred for the region inside the nebula, high-energy electrons and positrons produced by the two observed pulsars could not contribute significantly to the local measured cosmic-ray flux. The HAWC collaboration thus concluded that, under the assumption of isotropic and homogeneous diffusion, the two pulsars are ruled out as sources of the anomalous high-energy positron flux. Here, we argue that since the diffusion coefficient is likely not spatially homogeneous, the assumption leading to such conclusion is flawed. We solve the diffusion equation with a radially dependent diffusion coefficient, and show that the pulsars observed by HAWC produce potentially perfect matches to the observed high-energy positron fluxes. We also study the implications of inefficient diffusion within pulsar wind nebulae on Galactic scales, and show that cosmic rays are likely to have very long residence times in regions of inefficient diffusion. We describe how this prediction can be tested with studies of the diffuse Galactic emission. possibility has received considerable interest ever since the PAMELA result, but is very tightly constrained by the fact that no associated signal has been observed in gamma rays from dark matter annihilation, for example, in local dwarf spheroidal galaxies [16] or in nearby clusters of galaxies [17] For many years, an alternate, more mundane explanation has also been put forward [5,[18][19][20][21][22][23]23]: that middle-aged (τ ∼ 10 5 − 10 6 yr), nearby pulsars could accelerate, in their magnetosphere and, subsequently, in the surrounding shock with the interstellar medium, (primary) electrons and positrons to very high energy. The energetics of known candidate pulsars, as indicated by the pulsars' spin-down luminosity, is in the correct range to explain the observed excess positrons, as long as (1) the diffusion coefficient is D ∼ D ISM between the pulsar and Earth, and (2) a fraction of O(10%) of the spin-down luminosity is injected in positron-electron pairs [20,23].Recently, the HAWC (High-Altitude Water Cherenkov) Observatory confirmed earlier results from Milagro [24] and HAWC [25] and observed extended TeV emission surrounding two nearby pulsars, Geminga and Monogem (PSR B0656+14), among the candidate sources for the observed anomalous highenergy positrons [26]. As previously noted in [27], the spectrum and morphology from TeV gamma-ray observations can be used to infer features of the underlying high-energy electron-positron population responsible for the up-scattering of photons to TeV energies. In fact, Ref. [27] argued that HAWC observations available at the time [25] were entirely compatible, and actually supported, the hypothesis that the observed excess high-energy...

We present a radio search for WIMP dark matter in the Large Magellanic Cloud (LMC). We make use of a recent deep image of the LMC obtained from observations of the Australian Square Kilometre Array Pathfinder (ASKAP), and processed as part of the Evolutionary Map of the Universe (EMU) survey. LMC is an extremely promising target for WIMP searches at radio frequencies because of the large J-factor and the presence of a substantial magnetic field. We detect no evidence for emission arising from WIMP annihilations and derive stringent bounds on the annihilation rate as a function of the WIMP mass, for different annihilation channels. This work excludes the thermal cross section for masses below 480 GeV and annihilation into quarks.

We explore two possible scenarios to explain the observed γ-ray emission associated with the atypical globular cluster ω-Centauri: emission from millisecond pulsars (MSP) and dark matter (DM) annihilation. In the first case we predict the total number of MSPs in the globular cluster (n=45+22−16) using a new Bayesian method that combines the observational uncertainty in γ-ray counts with the intrinsic variation in individual pulsar luminosities. A DM interpretation is motivated by the possibility of ω-Centauri being the remnant core of an ancient dwarf galaxy hosting a surviving DM component. At least two annihilation channels, light quarks and muons, can plausibly produce the observed γ-ray spectrum. We are able to constrain the DM particle mass despite substantial uncertainties in the shape of the density profile (10 GeV ≲ mχ ≲ 30 GeV for annihilation into light quarks and 5 GeV ≲ mχ ≲ 9 GeV for annihilation into muons). We translate upper limits on ω-Centauri's remnant dark matter content into lower limits on the annihilation cross section (⟨ σ v⟩ ≳ 10−29 cm3 s −1 and ⟨ σ v⟩ ≳ 10−28 cm3 s −1 for quarks and muons respectively), taking into account the spatial extension of the DM halo. Moreover, there is a relatively small range of DM density profiles which are consistent with ω-Centauri's kinematics and stellar mass and can explain its γ-ray spectrum while simultaneously evading CMB constraints on dark matter annihilation. Further analysis of ω-Centauri's internal kinematics, and/or additional information on the resident MSP population will yield much stronger constraints and shed light about the origin of this otherwise mysterious γ-ray source.

The self-annihilation of dark matter particles with mass in the MeV range can produce gamma rays via prompt or secondary radiation. The annihilation rate for such light dark matter particles is however tightly constrained by cosmic microwave background (CMB) data. Here we explore the possibility of discovering MeV dark matter annihilation with future MeV gamma-ray telescopes taking into account the latest and future CMB constraints. We study the optimal energy window as a function of the dominant annihilation final state. We consider both the (conservative) case of the dwarf spheroidal galaxy Draco and the (more optimistic) case of the Galactic center. We find that for certain channels, including those with one or two monochromatic photon(s) and one or two neutral pion(s), a detectable gamma-ray signal is possible for both targets under consideration, and compatible with CMB constraints. For other annihilation channels, however, including all leptonic annihilation channels and two charged pions, CMB data rule out any significant signal of dark matter annihilation at future MeV gamma-ray telescopes from dwarf galaxies, but possibly not for the Galactic center.PACS numbers: 95.35.+d, 95.85.Pw, 98.52Wz

We present a systematic analysis on the possible presence of dark mass components inside globular clusters (GCs). A spherical Jeans analysis is applied to the stellar kinematics of 10 nearby GCs. On top of the mass distribution provided by the luminous stellar component, we add either dark matter (DM), described by an NFW or Burkert mass profile, or an intermediate mass black-hole (IMBH), described by a point-like mass. Their existence would have important implications in the context of indirect DM searches. After profiling over the stellar parameters, we find no evidence neither for DM nor for IMBH. Upper limits on the two components are reported.