Second dip as a signature of ultrahigh energy proton interactions with cosmic microwave background radiation

TL;DR

This paper proposes a new spectral feature at 6.3×10^{19} eV as a signature of ultrahigh energy protons interacting with the cosmic microwave background, potentially confirming the GZK effect.

Contribution

It introduces a nearly model-independent spectral dip as a signature of proton-CMB interactions, aiding in confirming the GZK effect.

Findings

Identifies a spectral dip at 6.3×10^{19} eV caused by proton interactions.

The dip's position is nearly model-independent.

Observation of this dip can confirm the GZK effect.

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 $E=6.3\times 10^{19}$ 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.