Some remarks on fundamental physical F-theory
  The purpose of this paper is to investigate the possibility of a physical 12-dimensional F-theory. We study the question of geometric interaction terms in the F-theory Lagrangians. We also introduce a new supergravity multiplet in dimension $(9,3)$ which is based on a particle with 3-dimensional timelike worldvolume. A construction of signature $(9,3)$ F-theory is given using dualities analogous to those considered by Hull, and possible matches of F-theory's low energy fields with the $(9,3)$-supergravity field content is given. Finally, preliminary suggestions are made regarding a possible phenomenological compactificaton of F-theory from dimension $(9,3)$ to $(3,1)$. 
Igor Kriz