Extremely high energy cosmic ray as the probe of new physics

We explore the influence of new physics on extremely high energy cosmic ray (EXCER) particles. In particular, we devote our mind to one example of new physics, unparticle stuff, on one specific process that EXECRs participate in, photopion production of the EXECR nucleon with 2.7K cosmic microwave background radiation (CMBR). Through computing the differential cross section of virtual exchange of unparticle in the $p+\gamma\to p+ \pi^0$ process, we acquire the general consequence of new physics on the EXECR propagation. It is astonishing but reasonable that due to the lowness of interaction energy $\sqrt{s}$, the new physics will play a nearly negligible role in EXECR interaction.