The KARMEN anomaly, light neutralinos and type II supernovae

The KARMEN experiment observes a time anomaly in events induced by pion decay at rest. This anomaly can be ascribed to the production of a new weakly interacting particle X with mass m_X\sim 34 MeV. We show that a recently proposed identification of the X particle with the lightest neutralino \chi in the frame work of the MSSM with broken R parity is in contradiction to optical observations of type II supernovae.Comment: 6 pages latex, 1 eps figure. Slightly revised (cf. title), matches published versio

Ultrahigh energy cosmic rays and new particle physics

The current status of the ultrahigh energy cosmic ray (UHE CR) enigma and several proposed solutions involving particle physics beyond the standard model are discussed. Emphasis is given to top--down models, and as a main example, supermassive dark matter as galactic source for UHE CR and the status of its experimental signatures (galactic anisotropy, chemical composition and clustering) is reviewed. Then different approaches to calculate fragmentation spectra of supermassive particles are discussed. Finally, it is argued that UHE neutrinos cannot be - neither directly or indirectly - responsible for the observed vertical air showers.Comment: 14 pages, 5 figures. Invited talk at ``CAPP-2K'', Verbier, July 200

Non-adiabatic oscillations of supernova neutrinos

The level-crossing probability, local and global adiabaticity conditions are discussed for 2-flavour neutrino oscillations in matter with arbitrary mixing angle $\theta$. Different approximations for the survival probability of supernova neutrinos are compared. Results of a combined likelihood analysis of the observed SN1987A neutrino signal and of the latest solar neutrino data including the recent SNO CC measurement are presented.Comment: 5 pages, 8 eps figures, JHEP style included. Talk presented at "Neutrino masses and mixings", Les Houches, June 2001, and at "EPS HEP 2001", Budapest, July 200

Ultrahigh energy neutrino interactions and weak-scale string theories

It has been suggested that ultrahigh energy neutrinos can acquire cross-sections approaching hadronic size if the string scale is as low as 1-10 TeV. In this case, the vertical air showers observed with energies above the Greisen-Zatsepin-Kuzmin cutoff at E approximately 6x10^{19} eV could be initiated by neutrinos which are the only known primaries able to travel long distances unimpeded. We have calculated the neutrino-nucleon cross-section due to the exchange of Kaluza-Klein excitations of the graviton in a field theoretical framework. We have found that the neutrino-nucleon cross section and the transferred energy per interaction are too small to explain vertical showers even in the most optimistic scenario.Comment: 7 pages, 3 figures; discussion of the sensitivity of Auger/Owl shortened, matches version to be publishe