  Antibranes provide some of the most generic ways to uplift Anti-de Sitter
flux compactifications to de Sitter, and there is a growing body of evidence
that antibranes placed in long warped throats such as the Klebanov-Strassler
warped deformed conifold solution have a brane-brane-repelling tachyon. This
tachyon was first found in the regime of parameters in which the backreaction
of the antibranes is large, and its existence was inferred from a highly
nontrivial cancellation of certain terms in the inter-brane potential. We use a
brane effective action approach, similar to that proposed by Michel, Mintun,
Polchinski, Puhm and Saad in arXiv:1412.5702, to analyze antibranes in
Klebanov-Strassler when their backreaction is small, and find a regime of
parameters where all perturbative contributions to the action can be computed
explicitly. We find that the cancellation found at strong coupling is also
present in the weak-coupling regime, and we establish its existence to all
loops. Our calculation indicates that the spectrum of the antibrane worldvolume
theory is not gapped, and may generically have a tachyon. Hence uplifting
mechanisms involving antibranes remain questionable even when backreaction is
small.
