Trans-Planckian particle creation in cosmology and ultrahigh energy cosmic rays

We consider observational constraints on the creation of particles induced by hypothetical trans-Planckian effects during the current stage of the Universe’s expansion. We show that compatibility with the diffuse γ-ray background measured by the EGRET experiment strongly restricts this creation. In particular, it rules out the possibility of detecting signatures of such short-distance effects in anisotropies of the cosmic microwave background radiation. On the other hand, the possibility that some part of ultrahigh-energy cosmic rays originates from new trans-Planckian physics remains open.