Weak Interactions in Supernova Cores and Saturation of Nucleon Spin Fluctuations

Extrapolation of perturbative nucleon spin fluctuation rates seems to suggest a strong suppression of weak interactions in supernova cores. We derive a new sum rule for the dynamical spin-density structure function which relates the spin fluctuation rate to the average nuclear interaction energy. For a bremsstrahlung like structure function profile we show that instead of strongly decreasing, the neutrino scattering cross section is roughly density independent and axion emission rates increase somewhat slower than the lowest order emissivities towards the center of a hot supernova core.Comment: 9 latex pages, 1 uuencoded postscript figure added via figures comman

Cosmic Radiation Constraints on Low String Scale and Extra Dimension Cross Sections

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 and brane world scenarios for gravity and compare them with cosmic ray data. Scenarios with effective energy scales in the TeV range and parton cross sections with linear or stronger growth with the center of mass energy appear strongly constrained or ruled out. String-inspired scenarios with infinite-volume extra dimensions may require a fundamental scale above 100 eV for which they are probably in conflict with gravity on parsec scales.Comment: 4 revtex pages, 1 postscript figur

Lectures on Astroparticle Physics

These are extended notes of a series of lectures given at the XIth Brazilian School of Cosmology and Gravitation. They provide a selection of topics at the intersection of particle and astrophysics. The first part gives a short introduction to the theory of electroweak interactions, with specific emphasize on neutrinos. In the second part we apply this framework to selected topics in astrophysics and cosmology, namely neutrino oscillations, neutrino hot dark dark matter, and big bang nucleosynthesis. The last part is devoted to ultra high energy cosmic rays and neutrinos where again particle physics aspects are emphasized. The often complementary role of laboratory experiments is also discussed in several examples.Comment: 42 pages, 12 figures, extended version of lectures given at the XIth Brazilian School of Cosmology and Gravitation, Rio de Janeiro, July 26 - August 4, 2004, prepared for AIP conference proceeding

Ultra-High Energy Cosmic Rays: A Probe of Physics and Astrophysics at Extreme Energies

The origin of cosmic rays is one of the major unresolved questions in astrophysics. In particular, the highest energy cosmic rays observed possess macroscopic energies and their origin is likely associated with the most energetic processes in the Universe. They thus provide a probe of physics and astrophysics at energies that are unreached in laboratory experiments. Theoretical explanations range from acceleration of charged particles in astrophysical environments to particle physics beyond the well established Standard Model, and processes taking place at the earliest moments of our Universe. Distinguishing between these scenarios requires detectors with effective areas in the 1000 km^2 range which are now under construction or in the planning stage. Close connections with gamma-ray and neutrino astrophysics add to the interdisciplinary character of this field.Comment: 21 latex pages, 4 postscript figures included; preprint version of recent Science review article; for journal version link see http://www.iap.fr/users/sigl/uhecrpub.htm

Magnetic horizons of ultra-high energy cosmic rays

The propagation of ultra-high energy cosmic rays in extragalactic magnetic fields can be diffusive, depending on the strength and properties of the fields. In some cases the propagation time of the particles can be comparable to the age of the universe, causing a suppression in the flux measured on Earth. In this work we use magnetic field distributions from cosmological simulations to assess the existence of a magnetic horizon at energies around 10$^{18}$ eV.Comment: 4 pages, 2 figures. Proceedings of the Particles and Nuclei International Conference (PANIC 2014