  We discuss the production of particles in relativistic heavy-ion collisions
through the mechanism of massive bremsstrahlung, in which massive mesons are
emitted during rapid nucleon acceleration. This mechanism is described within
the framework of classical hadrodynamics for extended nucleons, corresponding
to nucleons of finite size interacting with massive meson fields. This new
theory provides a natural covariant microscopic approach to relativistic
heavy-ion collisions that includes automatically spacetime nonlocality and
retardation, nonequilibrium phenomena, interactions among all nucleons, and
particle production. Inclusion of the finite nucleon size cures the
difficulties with preacceleration and runaway solutions that have plagued the
classical theory of self-interacting point particles. For the soft reactions
that dominate nucleon-nucleon collisions, a significant fraction of the
incident center-of-mass energy is radiated through massive bremsstrahlung. In
the present version of the theory, this radiated energy is in the form of
neutral scalar ($\sigma$) and neutral vector ($\omega$) mesons, which
subsequently decay primarily into pions with some photons also. Additional
meson fields that are known to be important from nucleon-nucleon scattering
experiments should be incorporated in the future, in which case the radiated
energy would also contain isovector pseudoscalar ($\pi^+$, $\pi^-$, $\pi^0$),
isovector scalar ($\delta^+$, $\delta^-$, $\delta^0$), isovector vector
($\rho^+$, $\rho^-$, $\rho^0$), and neutral pseudoscalar ($\eta$) mesons.
