Outstanding Problems in Particle Astrophysics

  title={Outstanding Problems in Particle Astrophysics},
  author={Thomas K. Gaisser},
The general features of the cosmic-ray spectrum have been known for a long time. Although the basic approaches to understanding cosmic-ray propagation and acceleration have also been well understood for many years, there are several questions of great interest that motivate the current intense experimental activity in the field. If the energy-dependence of the secondary to primary ratio of galactic cosmic rays is as steep as observed, why is the flux of PeV particles so nearly isotropic? Can… 
Non-thermal radiation from Type Ia supernova remnants
We present calculations of expected continuum emissions from Sedov-Taylor phase Type Ia supernova remnants (SNRs), using the energy spectra of cosmic ray (CR) electrons and protons from nonlinear
Cosmic Ray Acceleration by a Versatile Family of Galactic Wind Termination Shocks
There are two distinct breaks in the cosmic ray (CR) spectrum: the so-called “knee” around 3 × 1015 eV and the so-called “ankle” around 1018 eV. Diffusive shock acceleration (DSA) at supernova
Millicharged particles from the heavens: single- and multiple-scattering signatures
Abstract For nearly a century, studying cosmic-ray air showers has driven progress in our understanding of elementary particle physics. In this work, we revisit the production of millicharged
Large Scale Anisotropy of Cosmic Rays and Directional Neutrino Signals from Galactic Sources
We investigate the neutrino ⇋ cosmic ray connection for sources in the Galaxy in terms of two observables: the shape of the energy spectrum and the distribution of arrival directions. We also study
Atmospheric neutrinos in the context of muon and neutrino radiography
Using the atmospheric neutrinos to probe the density profile of the Earth depends on knowing the angular distribution of the neutrinos at production and the neutrino cross section. This paper reviews
Novel Constraints on Millicharged Particles from Cosmic Ray Data


Secondary Antiprotons and Propagation of Cosmic Rays in the Galaxy and Heliosphere
High-energy collisions of cosmic-ray nuclei with interstellar gas are believed to be the mechanism producing the majority of cosmic-ray antiprotons. Because of the kinematics of the process, they are
Cosmic rays and particle physics
The study of high energy cosmic rays is a diversified field of observational and phenomenological physics addressing questions ranging from shock acceleration of charged particles in various
Survey of data on primary cosmic-ray nuclei above 1014 eV
  • A. Hillas
  • Physics
    Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences
  • 1975
Primary cosmic-ray particles, detected by means of the extensive cascades they generate in the atmosphere, have been observed over a continuous range of energies up to 1020 eV, and apparently
Models of the knee in the energy spectrum of cosmic rays
Synchrotron Emission from Shock Waves in Active Galactic Nuclei
The origin of the sharp near infrared cutoff in the continuous energy distribution of many compact non-thermal sources (BL Lacs, OVVs, red quasars and certain jets) is considered under the assumption
Signatures of cosmic-ray interactions on the solar surface
The fluxes of neutrinos, gamma rays, antiprotons, neutrons, and antineutrons that result from collisions of high-energy Galactic cosmic rays with the solar atmosphere are estimated. The results are
Structure in the cosmic ray spectrum: an update
An update is given of the evidence from extensive air showers relating to our claim that there is `structure' in the energy spectrum of high-energy cosmic rays. The structure is explained, in our
Evidence for correlated changes in the spectrum and composition of cosmic rays at extremely high energies.
The Utah Fly's Eye detector has revealed a change in the cosmic ray composition which is correlated with structure in the all-particle energy spectrum, implying that the highest energy particles originate in the contemporary era of the Universe.
Gamma-ray emission from Cassiopeia A produced by accelerated cosmic rays
The nonlinear kinetic model of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to describe the relevant properties of Cassiopeia A (Cas A). In order to reproduce the SNR's observed
EGRET Observations of the Diffuse Gamma-Ray Emission from the Galactic Plane
The high-energy diffuse gamma-ray emission from the Galactic plane, |b| ≤ 10°, is studied using observations from the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray