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It has been argued that the observations of cosmic particles with energies in excess of $10^8$ TeV represent a puzzle. Its solution requires new astrophysics or new particle physics. We show that the latter is unlikely given that the scale…

This is a review of neutrino astronomy anchored to the observational fact that Nature accelerates protons and photons to energies in excess of $10^{20}$ and $10^{13}$ eV, respectively. Although the discovery of cosmic rays dates back close…

We introduce neutrino astronomy from the observational fact that Nature accelerates protons and photons to energies in excess of 10^{20} and 10^{13} eV, respectively. Although the discovery of cosmic rays dates back close to a century, we…

If there are large extra dimensions and the fundamental Planck scale is at the TeV scale, then the question arises of whether ultra-high energy cosmic rays might probe them. We study the neutrino-nucleon cross section in these models. The…

Astrophysical and atmospheric neutrinos are important probes of the powerful accelerators that produce cosmic-rays with EeV energies. Understanding these accelerators is a key goal of neutrino observatories, along with searches for…

With the discovery of a high-energy neutrino flux in the 0.1 PeV to PeV range from beyond the Earth's atmosphere with the IceCube detector, neutrino astronomy has achieved a major breakthrough in the exploration of the high-energy universe.…

Existing and planned observatories for cosmic neutrinos open up a huge window in energy from 10^7 to 10^17 GeV. Here, we discuss in particular the possibilities to use extremely energetic cosmic neutrinos as a diagnostic of astrophysical…

Searches for physics beyond the Standard Model of particle physics are performed at accelerators worldwide. Although having poorer detection capabilities and large beam uncertainties, ultra high energy cosmic ray (UHECR) experiments present…

Due to fundamental limitations of accelerators, only cosmic rays can give access to centre-of- mass energies more than one order of magnitude above those reached at the LHC. In fact, extreme energy cosmic rays (1018 eV - 1020 eV) are the…

The observed interaction energy of cosmic rays with atmospheric nuclei reaches up to a PeV in the center of mass. We compute nucleon-nucleon and nucleon-neutrino cross sections for various generic parton cross sections appearing in string…

The origin of Petaelectronvolt (PeV) astrophysical neutrinos is fundamental to our understanding of the high-energy Universe. Apart from the technical challenges of operating detectors deep below ice, oceans, and lakes, the phenomenological…

Recent observations of cosmic ray electrons from several instruments have revealed various degrees of deviation in the measured electron energy distribution from a simple power-law, in a form of an excess around TeV energies. An even more…

Astronomy at the highest energies observed must be performed by studying neutrinos rather than photons because the universe is opaque to photons of these energies. By making observations of neutrinos with energies above 10 EeV one can…

We introduce neutrino astronomy starting from the observational fact that Nature accelerates protons and photons to energies in excess of 10^{20} and 10^{13} eV, respectively. Although the discovery of cosmic rays dates back a century, we…

Neutrino astronomy offers the possibility to perform extra-galactic observations well beyond the photon absorption cutoff above 50 TeV. Based on observations of cosmic rays, we already know that astrophysical sources produce particles with…

While the general principles of high-energy neutrino detection have been understood for many years, the deep, remote geographical locations of suitable detector sites have challenged the ingenuity of experimentalists, who have confronted…

Candidate astrophysical acceleration sites capable of producing the highest energy cosmic rays (E > 10^{19.5} eV) appear to be at far greater distances than is compatible with their being known particles. The properties of a new particle…

The luminosity densities of high-energy cosmic radiations are studied to find connections among the various components, including high-energy neutrinos measured with IceCube and gamma rays with the Fermi satellite. Matching the cosmic-ray…

Even 100 years after the discovery of cosmic rays their origin remains a mystery. In recent years, TeV gamma-ray detectors have discovered and investigated many Galactic sources where particles are accelerated up to energies of 100 TeV.…

The astrophysical neutrinos discovered by IceCube have the highest detected neutrino energies --- from TeV to PeV --- and likely travel the longest distances --- up to a few Gpc, the size of the observable Universe. These features make them…