“…F-theory models of elliptic fibrations possessing a global section have been analyzed. Recent studies of such models can be found, e.g., in[4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49]. F-theory model constructions where one or more U(1) factors are formed are discussed, for example, in[4,7,8,10,…”