| Q-instantons (2008) | |||||||||||
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 χ and the dilaton φ, the Q-instanton is most conveniently described using a different set of fields (χ', T), where χ' 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 χ'. Discrete shifts of the axion χ' 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 {τ | τ ∈ PSL(2,R)/(SO(2)×PSL(2,Z))} the higher order R4 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 τ = i, ρ. | |||||||||||
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