title: Second dip as a signature of ultrahigh energy proton interactions with cosmic microwave background radiation.
abstract: We discuss as a new signature for the interaction of extragalactic ultrahigh energy protons with cosmic microwave background radiation a spectral feature located at E= 6.3 x 10(19) eV in the form of a narrow and shallow dip. It is produced by the interference of e+e(-)-pair and pion production. We show that this dip and, in particular, its position are almost model-independent. Its observation by future ultrahigh energy cosmic ray detectors may give the conclusive confirmation that an observed steepening of the spectrum is caused by the Greisen-Zatsepin-Kuzmin effect.
authors.affiliation: INFN, Laboratori Nazionali del Gran Sasso, I-67010 Assergi (AQ), Italy.
authors.forename: V
authors.initials: V
authors.lastname: Berezinsky
authors.forename: A
authors.initials: A
authors.lastname: Gazizov
authors.forename: M
authors.initials: M
authors.lastname: Kachelrieb