We present the results of the most complete scan of the parameter space for cosmic ray (CR) injection and propagation. We perform a Bayesian search of the main GALPROP parameters, using the MultiNest nested sampling algorithm, augmented by the BAMBI neural network machine-learning package. This is the first study to separate out low-mass isotopes (p, , and He) from the usual light elements (Be, B, C, N, and O). We find that the propagation parameters that best-fit , and He data are significantly different from those that fit light elements, including the B/C and ¹⁰Be/⁹Be secondary-to-primary ratios normally used to calibrate propagation parameters. This suggests that each set of species is probing a very different interstellar medium, and that the standard approach of calibrating propagation parameters using B/C can lead to incorrect results. We present posterior distributions and best-fit parameters for propagation of both sets of nuclei, as well as for the injection abundances of elements from H to Si. The input GALDEF files with these new parameters will be included in an upcoming public GALPROP update.

The annihilation of dark matter into neutrinos over a range of dark matter masses from $\mathrm{MeV}/c^2$ to $\mathrm{ZeV}/c^2$ is reviewed. Thermally produced models of dark matter are expected to self-annihilate to standard model products. As no such signal has yet been detected, neutrino detectors are turned to in order to constrain the “most invisible channel.” The experimental techniques that are used to detect neutrinos are reviewed, and the expected contributions to the neutrino flux at current and upcoming neutrino experiments is revisited. Updated constraints are placed on the dark matter self-annihilation cross section to neutrinos $⟨\sigma v⟩$ using the most recent data, and the sensitivity of upcoming experiments such as Hyper-Kamiokande, Deep Underground Neutrino Experiment (DUNE), and IceCube Gen2 is forecasted. Where possible, limits and projections are scaled to a single set of dark matter halo parameters for consistent comparison. Galactic and extragalactic signals of $s$-, $p$-, and $d$-wave annihilation processes directly into neutrino pairs are considered, yielding constraints that range from $⟨\sigma v⟩\sim 2.5\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at $30\mathrm{MeV}/c^2$ to ${10}^{-17}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at ${10}^{11}\mathrm{Ge}\mathrm{V}/c^2$. Experiments that report directional and energy information of their events provide much stronger constraints, outlining the importance of making such data public.

A full energy and flavor-dependent analysis of the three-year high-energy IceCube neutrino events is presented. By means of multidimensional fits, we derive the current preferred values of the high-energy neutrino flavor ratios, the normalization and spectral index of the astrophysical fluxes, and the expected atmospheric background events, including a prompt component. A crucial assumption resides on the choice of the energy interval used for the analyses, which significantly biases the results. When restricting ourselves to the $\sim 30\mathrm{TeV}–3\mathrm{PeV}$ energy range, which contains all the observed IceCube events, we find that the inclusion of the spectral information improves the fit to the canonical flavor composition at Earth, $(1:1:1{)}_{\oplus }$, with respect to a single-energy bin analysis. Increasing both the minimum and the maximum deposited energies has dramatic effects on the reconstructed flavor ratios as well as on the spectral index. Imposing a higher threshold of 60 TeV yields a slightly harder spectrum by allowing a larger muon neutrino component, since above this energy most atmospheric tracklike events are effectively removed. Extending the high-energy cutoff to fully cover the Glashow resonance region leads to a softer spectrum and a preference for tau neutrino dominance, as none of the expected electron (anti)neutrino induced showers have been observed so far. The lack of showers at energies above 2 PeV may point to a broken power-law neutrino spectrum. Future data may confirm or falsify whether the recently discovered high-energy neutrino fluxes and the long-standing detected cosmic rays have a common origin.

The IceCube experiment has recently reported the observation of 28 high-energy ($>30\mathrm{TeV}$) neutrino events, separated into 21 showers and 7 muon tracks, consistent with an extraterrestrial origin. In this Letter, we compute the compatibility of such an observation with possible combinations of neutrino flavors with relative proportion $({\alpha }_e:{\alpha }_{\mu }:{\alpha }_{\tau }{)}_{\oplus }$. Although the $7:21$ track-to-shower ratio is naively favored for the canonical $(1:1:1{)}_{\oplus }$ at Earth, this is not true once the atmospheric muon and neutrino backgrounds are properly accounted for. We find that, for an astrophysical neutrino $E^{-2}$ energy spectrum, $(1:1:1{)}_{\oplus }$ at Earth is disfavored at 81% C.L. If this proportion does not change, 6 more years of data would be needed to exclude $(1:1:1{)}_{\oplus }$ at Earth at $3\sigma$ C.L. Indeed, with the recently released 3-yr data, that flavor composition is excluded at 92% C.L. The best fit is obtained for $(1:0:0{)}_{\oplus }$ at Earth, which cannot be achieved from any flavor ratio at sources with averaged oscillations during propagation. If confirmed, this result would suggest either a misunderstanding of the expected background events or a misidentification of tracks as showers, or even more compellingly, some exotic physics which deviates from the standard scenario.

We compute the bounds on the dark matter (DM) annihilation cross section using the most recent Cosmic Microwave Background measurements from WMAP9, SPT'11 and ACT'10. We consider DM with mass in the MeV–TeV range annihilating 100% into either an e+e− or a μ+μ− pair. We consider a realistic energy deposition model, which includes the dependence on the redshift, DM mass and annihilation channel. We exclude the canonical thermal relic abundance cross section (σv = 3 × 10−26cm3s−1) for DM masses below 30 GeV and 15 GeV for the e+e− and μ+μ− channels, respectively. A priori, DM annihilating in halos could also modify the reionization history of the Universe at late times. We implement a realistic halo model taken from results of state-of-the-art N-body simulations and consider a mixed reionization mechanism, consisting on reionization from DM as well as from first stars. We find that the constraints on DM annihilation remain unchanged, even when large uncertainties on the halo model parameters are considered.