Monatomic gas as a singular limit of relativistic theory of 15 moments with non-linear contribution of microscopic energy of molecular internal mode

Recently a new relativistic model of polyatomic gases has been proposed, by Arima-CarrisiPennisi-Ruggeri (2022), in the context of Rational Extended Thermodynamics. It is based on a hierarchy of 15 moments of the Boltzmann-Chernikov equation that appropriately takes into account the non-linear contribution of the microscopic total energy of the molecule (the sum of the rest energy and of the energy of the molecular internal modes). In this paper, in the singular limit, under initial conditions compatible with monatomic gases, we prove that the 15-moments model for polyatomic gases leads, to the well-known 14-moments model of monatomic gases.