X-ray binary systems are expected to emit ultrahigh-energy photons and neutrinos in comparable numbers. Energies of several TeV in the center-of-mass frame in collisions with air nuclei are likely to be present in such beams. These beams can be used to probe the substructure of leptons and quarks by means not available in accelerator-based experiments in the forseeable future. In composite models with leptons and quarks sharing some strongly interacting subconstituents, an increased neutrino interaction cross section is expected above a certain critical energy. Such models lead to some characteristic signatures of the onset of ‘‘new physics.’’ Some experiments are proposed to observe the new physics and to test whether the new types of events are caused by neutrinos.

• Received 11 April 1988

DOI:https://doi.org/10.1103/PhysRevD.38.2833