Description
I will describe different aspects of effective actions in string feld
theory. First, I will discuss how to compute the effective action and
how to obtain its algebraic properties from the UV action. This includes
obtaining the effective gauge invariance, the difference between gauge
fixing and integrating out auxiliary fields (like Nakanishi--Lautrup),
and the inclusion of a source. Second, I will show that the heterotic
effective action of the zero-momentum massless fields reproduces the
commutator-squared term from the Yang--Mills action. The computation
uses the concept of localization, which allows to get the quartic term
without knowing explicitly the quartic interaction of the UV theory.