Calculable effects

Abstract

We identify and evaluate a class of physical amplitudes in four-dimensional N = 4 superstring theory, which receive, in the weak coupling limit, contributions of order e −1/λ , where λ is the type II superstring coupling constant. They correspond to four-derivative F 1 interaction terms involving the universal type II dilaton supermultiplet. The exact result, obtained by means of a one-loop computation in the dual heterotic theory compactified on T 6 , is compared with the perturbation theory on the type II side, and the e −1/λ contributions are associated to non-perturbative effects of Euclidean solitons (D-branes) wrapped on K3 × T 2 . The ten-dimensional decompactification limit on the type IIB side validates the recent conjecture for the D-instanton-induced R 4 couplings.

Towards matter ination in heterotic string theory

“…It relies on non-perturbative corrections to the superpotential from gaugino condensation in combination with non-perturbative corrections to the Kähler potential. These nonperturbative corrections can be either of a field-theoretic [98] or a stringy origin [99] (see also [100][101][102]). Field-theory instantons scale like e −1/g 2 , while string theory instanton effects scale like e −1/g , where g is the coupling constant.…”

Low scale unification, Newton's law and extra dimensions

“…A well known result in the weakly coupled heterotic string theory is that the string scale, is of the order of the Planck mass M P [1]. Recent developments have revealed the possibility that the string scale can be arbitrarily low in Type I and Type IIB theories [2,3,4,5,6,7,8,9,10,11].…”

Cosmological solutions of type II superstrings

“…In type IIB theory, in particular, nonperturbative effects are intimately related to the SL(2,Z) symmetry of the theory [6] and a conjecture for their structure has been put forward in Ref. [7], which gives the tree and one-loop corrections to the R 4 term besides the instanton ones; this conjecture has been validated in [8]. In type IIA theories such non-perturbative corrections do not exist, essentially because there are no finite-action instantons so that the R 4 term is given entirely by the sum of the perturbative tree-level and one-loop terms.…”