  We put forward the following, physically motivated premise for constructing a
theory that underlies the standard model in four-dimensional space-time: The
Euler-Lagrange equations of such a theory formally resemble some equations of
motion underlying fluid-dynamics equations in the kinetic theory of gases.
Following this premise, we point out Lorentz-invariant Lagrangians whose
Euler-Lagrange equations contain a subsystem equivalent to the Euler-Lagrange
equations of the standard model with covariantly regularized propagators.
