Potenziale efficace per un sistema DD separato in String Field Theory ​

In this thesis we use the framework of Open String Field Theory (OSFT) to evaluate analytically the tree-level effective action of unstable D-brane systems . Starting with the method developed by Berkovits and Schnabl we obtain the general form of the tree-level effective action in Witten Bosonic OSFT and in super OSFT up to the quartic order. In doing this we discover a previously ignored zero-momentum contribution which arises whenever a massless state is exchanged in the four point amplitude and we estimate the contribution of this new term. We apply our results to a system of two parallel D-branes and on a brane-antibrane pair both separated by a critical distance at which the tachyonic stretched strings between the two branes are exactly massless. We discuss how typical divergences that would appear in usual String Theory in strict zero momentum calculations are eliminated without ambiguity in the context of String Field Theory. ​