Double-soft behavior of massless closed strings interacting with any number of closed string tachyons

We calculate the simultaneous double-soft limit of two massless closed strings scattering with any number of closed string tachyons to the subleading order at the tree level. The limit factorizes the scattering amplitude into a double-soft factor multiplying the pure tachyon subamplitude, suggesting a universal double-soft theorem for the massless closed string. We confirm an existing result for the double-soft graviton in an on-shell equivalent, but different form, while also establishing the double-soft factorization behavior of the string dilaton and of the Kalb-Ramond state, as well as the mixed graviton-dilaton case. We also show that the simultaneous and consecutive double-soft theorems are consistent with each other. We furthermore provide a complete field theory diagrammatic view on our result, which enables us in particular to establish a four-point interaction vertex for two tachyons and two massless closed string states, as well as the missing in field theory of three-point interaction of two massless closed string state and one tachyon.

ON THE GAUGE/GRAVITY CORRESPONDENCE AND THE OPEN/CLOSED STRING DUALITY

In this paper we review the conditions for the validity of the gauge/gravity correspondence in both supersymmetric and nonsupersymmetric string models. We start by reminding what happens in type IIB theory on the orbifolds ℂ2/ℤ2and ℂ3/(ℤ2x ℤ2), where this correspondence beautifully works. In these cases, by performing a complete stringy calculation of the interaction among D3-branes, it has been shown that the fact that this correspondence works is a consequence of the open/closed duality and of the absence of threshold corrections. Then we review the construction of type 0 theories with their orbifolds and orientifolds having spectra free from both open and closed string tachyons and for such models we study the validity of the gauge/gravity correspondence, concluding that this is not a peculiarity of supersymmetric theories, but it may work also for nonsupersymmetric models. Also in these cases, when it works, it is again a consequence of the open/closed string duality and of vanishing threshold corrections.