D-term inflation in superstring theories Original Research Article

An inflationary stage dominated by a D-term avoids the slow-roll problem of inflation in supergravity and may emerge in theories with a non-anomalous or anomalous U(1) gauge symmetry. The most intriguing and commonly invoked possibility is that the Fayet-Iliopoulos D-term triggering inflation is the one emerging in superstring theories. We discuss the complications one has to face when trying to build up a successful D-term inflationary scenario in superstring models. In particular, we show that the “vacuum shifting” phenomenon of string theories is usually very efficient even in the early Universe, thus preventing inflation from taking place. On the other hand, when D-term inflation is free to occur, the presence of a plethora of fields and several non-anomalous additional Abelian symmetries in string theories may help in reconciling the value of the Fayet-Iliopoulos D-term required by the COBE normalization with the value predicted by string theories. We also show that in superstring D-term inflation gravitinos are likely to pose no cosmological problem.