7 papers
Null fluid gravitational fields on Kerr manifolds and optical lifts of Sasaki structures
Masoud Ganji, Cristina Giannotti, Andrea Spiro
Building on the characterisation in [C. D. Hill, J. Lewandowski and P. Nurowski, Indiana Univ. Math. J. 57 (2008), 3131--3176] of 4-dimensional Lorentzian metrics adapted to an opt…
Black holes and black regions, horizons and barriers in Lorentzian manifolds
Cristina Giannotti, Andrea Spiro
We prove that if S is a time-oriented null hypersurface of a Lorentzian n-manifold (M, g), the causal world-lines, which intersect transversally S and are time-oriented in a compat…
Flows of vector fields and the Kalman Theorem
Fabio Bagagiolo, Cristina Giannotti, Andrea Spiro +1
We give two proofs of the Kalman Theorem, alternative to the most common ones, which infer such a classical result of Control Theory using just very basic facts on flows of vector…
Einstein manifolds with optical geometries of Kerr type
Masoud Ganji, Cristina Giannotti, Gerd Schmalz +1
We classify the Ricci flat Lorentzian -manifolds satisfying three particular conditions, encoding and combining some crucial features of the Kerr metrics and the Robinson-Trautm…
Distributions and controllability problems (II)
Cristina Giannotti, Andrea Spiro, Marta Zoppello
In [C. Giannotti, A. Spiro, M. Zoppello, {\it Distributions and controllability problems (I)}, preprint posted on ArXiv (2024)], we introduced a new approach to the real analytic n…
Distributions and controllability problems (I)
Cristina Giannotti, Andrea Spiro, Marta Zoppello
We consider a non-linear real analytic control system of first order , with controls in a connected open set …
Proving the Chow-Rashevskii Theorem à la Rashevskii
Cristina Giannotti, Andrea Spiro, Marta Zoppello
We give a new independent proof of a generalised version of the theorem by Rashevskii, which appeared in [Uch. Zapiski Ped. Inst. K. 2 (1938), 83 -- 94] and from which the classica…