Phenomenology of heterotic and type II orientifold string models



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Cryptons are metastable bound states of fractionally-charged particles that arise generically in the hidden sectors of models derived from heterotic string. We study their properties and decay modes in a speci?c ?ipped SU(5) model with long-lived four-particle spin-zero bound states called tetrons. The expected masses and lifetimes of the neutral tetrons make them good candidates for cold dark matter (CDM), and a potential source of the ultra-high energy cosmic rays (UHECRs) which have been observed, whereas the charged tetrons would have decayed in the early Universe. We calculate the spectra of ultra-high-energy cosmic rays (UHECRs) in an ex?plicit top-down model based on the decays of metastable neutral ?crypton? states. For all the decay operators, the total UHECR spectra are compatible with the available data. Also, the fractions of photons are compatible with all the published upper limits, but may be detectable in future experiments. We also construct several intersecting D-brane models on a variety of orientifold backgrounds. In particular, we construct ?ipped SU(5), Pati-Salam, and MSSM-like models. The phenomenological properties of these models are studied. For one model in particular, we ?nd that we may explain the quark masses and mixings, the tau lepton mass, and generate small neutrino masses via the see-saw mechanism.