Strong Hamel functions and symmetries

Abstract

A strong Hamel function is a Hamel function that is the geodesic derivative of some 0-homogeneous function. We prove that strong Hamel functions induce dual symmetries and dynamical symmetries and provide the conditions such that these symmetries are induced by strong Hamel functions. We show that projective deformations by strong Hamel functions preserve the $\chi$-curvature and analyse the relationship with some other functions (Funk and weak Funk functions) preserving curvature tensors under projective deformations. In the flat case, any Hamel function is a strong Hamel function.