Un nuovo gauge per le azioni effettive nelle teorie di campo di stringa

In this thesis we study the effective formulation of Witten bosonic open string field theory (OSFT) and Berkovits open superstring field theory (OSSFT), integrating out the heavy degrees of freedom at classical level, to build the tree-level effective action. The central goal of this research is to develop a new method to compute exactly all effective couplings at each order. Previously such a task was not possible due to “anomalies”, which correspond to non-computable terms that show up starting from the quartic order. The presence of these terms hindered the complete construction of the tree-level effective action. The elimination of anomalies is possible because they correspond to a field redefinition effect, so the idea is to choose an appropriate gauge fixing to remove these terms. The gauge that does the job is the so-called pseudo-Siegel gauge, which is a gauge that changes order by order in perturbation theory. To see the mechanism at work, we will apply this new formalism to a concrete example, a system consisting of two parallel D(p)-branes along a common Dirichlet direction, separated by a critical distance, so that the stretched tachyons are massless. In this configurations we will evaluate explicity cubic, quartic and quintic effective couplings. The latter can be computed only thanks to the new method. In these explicit evaluation it is crucial to regularize the infrared divergences which arise respectively from the tachyons that live on the same D(p)-brane and the weight zero massless states stretched between the two branes. Finally, we will adapt this new formalism to Berkovits theory and we will be able to proceed in the explicit calculation of the effective couplings. In this case the reference system will be two D(P)-branes with opposite Ramond-Ramond charge, the so-called D −D system.