On weakly stretch Kropina metrics

In this paper, we study weakly stretch Kropina metrics and prove a rigidity theorem. We show that the associated one-form of a weakly stretch Kropina metric is conformally Killing with respect to the associated Riemannian metric. We find that any weakly stretch Kropina metric has vanishing S-curvature. Then, we prove that every weakly stretch Kropina metric is a Berwald metric. It turns out that every R-quadratic Kropina metric is a Berwald metric. Finally, we show that every positively complete C-reducible metric is R-quadratic if and only if it is Berwaldian.