The classical cosmological constant of open-closed string field theory

A bstract We consider deformations of D-brane systems induced by a change in the closed string background framework bosonic open-closed field theory, where it is possible to unambiguously tame infrared divergences originating from both open and degenerations. classical solution induces tadpole for strings which shifts vacuum generates cosmological constant composed two terms: one directly related other depends on shift. show that only sum these terms invariant under SFT gauge transformations therefore an observable. conjecture this observable universally proportional shift world-sheet disk partition function between starting undeformed final deformed background, typically includes also coupling constant. test considering perturbative describing Narain compactification and, constant, we reproduce expected g -function various D-branes living compactification. In doing are able identify surprising at second order deformation.