  We are interested in the energy-momentum relation for a moving composite in
relativistic quantum mechanics in many-particle Dirac models. For a manifestly
covariant model one can apply the Lorentz transform to go from the rest frame
to a moving frame to establish an energy-momentum relation of the form
$\sqrt{(M^*c^2)^2+c^2|{\bf P}|^2}$ where $M^*$ is the kinematic mass. However,
the many-particle Dirac model is not manifestly covariant, and some other
approach is required. We have found a simple approach that allows for a
separation of relative and center of mass contributions to the energy. We are
able to define the associated kinematic energy and determine the
energy-momentum relation. Our result can be expressed as a modified deBroglie
relation of the form
  $$ \hbar \omega ({\bf P}) = <\Phi' | \sum_j {m_j \over M} \beta_j | \Phi' >~
\sqrt{[M^*({\bf P}) c^2]^2 + c^2 |{\bf P}|^2} $$
  where the kinematic mass $M^*$ will depend on the total momentum ${\bf P}$
for a general noncovariant potential. The prefactor that occurs we associate
with a time dilation effect, the existence of which has been discussed
previously in the literature.
