Q-instantons
arXiv:0801.4956 · doi:10.1088/1126-6708/2008/06/028
Abstract
We construct the half-supersymmetric instanton solutions that are electric-magnetically dual to the recently discussed half-supersymmetric Q7-branes. We call these instantons `Q-instantons'. Whereas the D-instanton is most conveniently described using the RR axion Ïand the dilaton Ï, the Q-instanton is most conveniently described using a different set of fields Ï' and T, where Ï' is an axionic scalar. The real part of the Q-instanton on-shell action is a function of T and the imaginary part is linear in Ï'. Discrete shifts of the axion Ï' correspond to PSL(2,Z) transformations that are of finite order. These are e.g. pure S-duality transformations relating weak and strongly coupled regimes. We argue that near each orbifold point of the quantum axion-dilaton moduli space PSL(2,Z)\PSL(2,R)/SO(2) the higher order R^4 terms in the string effective action contain contributions from an infinite sum of single multiply-charged instantons with the Q-instantons corresponding to the orbifold points Ï=i,Ïwhere Ïis the complex axion-dilaton field.
29 pages, 1 figure