  Non-electromagnetic emissions from high energy particles in extreme
environments has been studied in the literature by using several variations of
the semi-classical formalism. The detailed mechanisms behind such emissions are
of great astrophysical interest since they can alter appreciably the associated
energy loss rates. Here, we review the role played by the source proper
acceleration $a$ in the particle production process. The acceleration $a$
determines the typical scale characterizing the particle production and,
moreover, if the massive particle production is inertially forbidden, it will
be strongly suppressed for $a$ below a certain threshold. In particular, we
show that, for the case of accelerated protons in typical pulsar
magnetospheres, the corresponding accelerations $a$ are far below the pion
production threshold.
