Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5–10 improvement in sensitivity in the 100 GeV–10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.

We study high-energy neutrino production in inner jets of radio-loud active galactic nuclei (AGN), taking into account effects of external photon fields and the blazar sequence. We show that the resulting diffuse neutrino intensity is dominated by quasar-hosted blazars, in particular, flat spectrum radio quasars, and that PeV-EeV neutrino production due to photohadronic interactions with broadline and dust radiation is unavoidable if the AGN inner jets are ultrahigh-energy cosmic-ray (UHECR) sources. Their neutrino spectrum has a cutoff feature around PeV energies since target photons are due to $\mathrm{Ly}$\alpha${}$ emission. Because of infrared photons provided by the dust torus, neutrino spectra above PeV energies are too hard to be consistent with the IceCube data unless the proton spectral index is steeper than 2.5, or the maximum proton energy is $$\lesssim${}100\text{ }\text{ }\mathrm{PeV}$. Thus, the simple model has difficulty in explaining the IceCube data. For the cumulative neutrino intensity from blazars to exceed $$\sim${}{10}^{$-${}8}\text{ }\text{ }\mathrm{GeV}\text{ }{\mathrm{cm}}^{$-${}2}\text{ }{\mathrm{s}}^{$-${}1}\text{ }{\mathrm{sr}}^{$-${}1}$, their local cosmic-ray energy generation rate would be $$\sim${}10\char21{}100$ times larger than the local UHECR emissivity but is comparable to the averaged $$\gamma${}$-ray blazar emissivity. Interestingly, future detectors such as the Askaryan Radio Array can detect $$\sim${}0.1\char21{}1\text{ }\text{ }\mathrm{EeV}$ neutrinos even in more conservative cases, allowing us to indirectly test the hypothesis that UHECRs are produced in the inner jets. We find that the diffuse neutrino intensity from radio-loud AGN is dominated by blazars with $$\gamma${}$-ray luminosity of $$\gtrsim${}1{0}^{48}\text{ }\text{ }\mathrm{erg}\text{ }{\mathrm{s}}^{$-${}1}$, and the arrival directions of their $$\sim${}1\char21{}100\text{ }\text{ }\mathrm{PeV}$ neutrinos correlate with the luminous blazars detected by Fermi.

Weakly interacting massive particles (WIMPs) are a theoretical class of particles that are excellent dark matter candidates. WIMP annihilation or decay may produce essentially monochromatic $\gamma$ rays detectable by the Fermi Large Area Telescope (LAT) against the astrophysical $\gamma$-ray emission of the Galaxy. We have searched for spectral lines in the energy range 5–300 GeV using 3.7 years of data, reprocessed with updated instrument calibrations and an improved energy dispersion model compared to the previous Fermi-LAT Collaboration line searches. We searched in five regions selected to optimize sensitivity to different theoretically motivated dark matter density distributions. We did not find any globally significant lines in our a priori search regions and present 95% confidence limits for annihilation cross sections of self-conjugate WIMPs and decay lifetimes. Our most significant fit occurred at 133 GeV in our smallest search region and had a local significance of 3.3 standard deviations, which translates to a global significance of 1.5 standard deviations. We discuss potential systematic effects in this search, and examine the feature at 133 GeV in detail. We find that the use both of reprocessed data and of additional information in the energy dispersion model contributes to the reduction in significance of the linelike feature near 130 GeV relative to significances reported in other works. We also find that the feature is narrower than the LAT energy resolution at the level of 2 to 3 standard deviations, which somewhat disfavors the interpretation of the 133 GeV feature as a real WIMP signal.