Instantons in the Double-Tensor Multiplet

TL;DR

The paper addresses instanton corrections to the hypermultiplet moduli space in type II string compactifications by formulating the Euclidean double-tensor multiplet in supergravity and deriving a Bogomol'nyi bound. It shows the Euclidean action is bounded below and saturable by BPS configurations, constructing three O(2) classes of instanton solutions characterized by topological charges and asymptotic scalar values. The instanton actions depend on the string coupling and include a novel Δχ-dependent term that persists at fixed g_s, highlighting new nonperturbative contributions to the hypermultiplet metric. The authors discuss duality to the universal hypermultiplet, the role of boundary terms, and outline future work to include fermions, zero modes, and matching to ten-dimensional brane pictures and quaternionic geometry results.

Abstract

The double-tensor multiplet naturally appears in type IIB superstring compactifications on Calabi-Yau threefolds, and is dual to the universal hypermultiplet. We revisit the calculation of instanton corrections to the low-energy effective action, in the supergravity approximation. We derive a Bogomolny'i bound for the double-tensor multiplet and find new instanton solutions saturating the bound. They are characterized by the topological charges and the asymptotic values of the scalar fields in the double-tensor multiplet.