On the particle production threshold for ultra-relativistic accelerated   protons
  Non-electromagnetic emission from cosmic ray particles accelerated in extreme environments has been studied using different variations of semi-classical formalisms. As the energy loss mechanisms of such particles is of great interest, one must improve in some sense the previously intuitive description of classical sources in the presence of fields. In this brief note we evaluate the role played by the classical and dimensional proper acceleration of a particle in radiation processes. One intends to show that the introduction of the acceleration as a measure parameter gives an adequate scale for considering the processes of massive particle emission. If the acceleration threshold is not attained one is considering a regime where the processes of massive particle production are suppressed. The analysis is performed in a semiclassical formalism once applied in different contexts and already checked for consistency in a serie of papers. As a further application of the results we evaluate the possibility of a non negligible meson production by protons accelerated in the framework of polar cap models operating in electromagnetic fields of pulsars. It is shown that inside a systems endowed with magnetic fields B\geq 10^{12} G the meson emission by protons must not be disregarded. 
Douglas Fregolente (Campina Grande Federal U., CFP)