Hyperbolic partial differential equations for the description of mass-less particles

Hyperbolic systems of partial differential equations are very important for physical applications because they satisfy the causality principle and lead to finite propagation of shocks waves. Many of these cases have been considered in Extended Thermodynamics. Here a new example of physical application is obtained by applying the new theory of the two blocks of balance equations to the case of mass-less particles, in the relativistic context.