Variational theory of the Ricci curvature tensor dynamics Claudio Cremaschini, Jiří Kovář, Zdeněk Stuchlík and Massimo Tessarotto Eur. Phys. J. C, 81 11 (2021) 1030 Published online: 25 November 2021 DOI: 10.1140/epjc/s10052-021-09847-6