On the two-systole of real projective spaces

Abstract

We establish an integral-geometric formula for minimal two-spheres inside homogeneous three-spheres, and use it to provide a characterisation of each homogeneous metric on the three-dimensional real projective space as the unique metric with the largest possible two-systole among metrics with the same volume in its conformal class.

10 pages. Minor typos corrected, keywords added. Submitted version