Relativistic mass tensor with geometric interpretation

We derive a relativistic mass tensor (dyadic or matrix) whose origin and properties have a direct geometric interpretation in terms of projection operators related to the particle's world line and local inertial frame in Minkowski space, yet whose eigenvalues are simply the longitudinal (m/sub l/) and the transverse (m/sub t/) mass. Writing the noncovariant equations of motion (EOM) for a point particle in terms of this mass tensor bridges the gap between the compact but sterile form of the Lorentz covariant EOM and the usual (''unwieldy'') noncovariant EOM in which m/sub l/ and m/sub t/ appear. General expressions for 3- and 4-space mass (inverse mass) tensors are presented in terms of the system Lagrangian (Hamiltonian)