3 papers
gr-qc2026
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…
gr-qc2025
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…
math.OC2025
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…