Il modello di Klein e la cosmologia (Q1218775)

This work is composed of two parts. In the first, by applying the method of contraction of a group with respect to its subgroup by Inönü and Wigner, from the model of de Sitter-Castelnuovo based on the group of Fantappiè the author newly obtains a series of well-known models of the Universe: the model of Hooke, the model of Bacry, the model of Minkowski, the model of Newton, and the model of Caroll. In the second part, by using his previous results [Gli spazi di Cartan e le teorie unitarie. Collect. Math. 21, 149--171 (1970); 23, 105--128 (1972; Zbl 0275.76049)] he investigates wave propagation in relativistic hydrodynamics, projective hydrodynamics, ideal magnetohydrodynamics, and ideal projective magnetohydrodynamics. Finally the generalized d'Alembert equation is considered, which is a partial differential equation of mixed type of Tricomi.