Tudor S. Ratiu is a Romanian-American mathematician. His main works are in mechanics and dynamical systems from the point of view of differential geometry.

Jerrold E Marsden, Tudor S Ratiu, Introduction to mechanics and symmetry: a basic exposition of classical mechanical systems, Springer 2013

Juan-Pablo Ortega, Tudor S Ratiu, Momentum maps and Hamiltonian reduction, Progress in Mathematics 222, Birkhäuser 2003.

Daniel Beltiţă, Tudor S. Ratiu, Geometric representation theory for unitary groups of operator algebras, Advances in Mathematics 208:1 (2007) 299–317 doi arXiv:math.RT/0501057

François Demoures, François Gay-Balmaz, Tudor S. Ratiu, Multisymplectic variational integrators and space/time symplecticity, Analysis and Applications 14:03 (2016) 341–391 arXiv:1310.4772doi