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Abstract

We review and extend results on higher-curvature corrections to different
configurations describing a superposition of heterotic strings, KK monopoles,
solitonic 5-branes and momentum waves. Depending on which sources are present,
the low-energy fields describe a black hole, a soliton or a naked singularity.
We show that this property is unaltered when perturbative higher-curvature
corrections are included, provided the sources are fixed. On the other hand,
this character may be changed by appropriate introduction (or removal) of
sources regardless of the presence of curvature corrections, which constitutes
a non-perturbative modification of the departing system. The general system of
multicenter KK monopoles and their 5-brane charge induced by higher-curvature
corrections is discussed in some detail, with special attention paid to the
possibility of merging monopoles. Our results are particularly relevant for
small black holes (Dabholkar-Harvey states, DH), which remain singular after
quadratic curvature corrections are taken into account. When there are four
non-compact dimensions, we notice the existence of a black hole with regular
horizon whose entropy coincides with that of the DH states, but the charges and
supersymmetry preserved by both configurations are different. A similar
construction with five non-compact dimensions is possible, in this case with
the same charges as DH, although it fails to reproduce the DH entropy and
supersymmetry. No such configuration exists if $d>5$, which we interpret as
reflecting the necessity of having a 5-brane wrapping the compact space.