Wilsonian Effective Field Theory and String Theory

We argue that deriving an effective field theory from string theory requires a Wilsonian perspective with a physical cutoff. Employing proper time regularization we demonstrate the decoupling of states and contrast this with what happens in dimensional regularization. In particular we point out that even if the cosmological constant (CC) calculated from some classical action at some ultra-violet scale is negative, this does not necessarily imply that the CC calculated at cosmological scales is also negative, and discuss the possible criteria for achieving a positive CC starting with a CC at the string/KK scale which is negative. Obviously this has implications for swampland claims.