Higher Spins and String Interactions

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In this Thesis we address the issue of consistent higher-spin interactions taking String Theory as a "theoretical laboratory". We thus arrive at a simple expression encompassing all three-point amplitudes for states belonging to the first Regge trajectory of the open bosonic string, that are described by fully symmetric tensors, and we explicitly construct the corresponding effective action at the cubic level. A gauge invariant structure is seen to emerge in the massless limit, in line with long-held expectations for high-energy string scattering. We also study some properties of the field theory amplitudes that arise from our effective Lagrangian and involve the exchange of infinitely many higher-spin excitations. These results and other related developments will soon appear in a joint publication with A. Sagnotti