superstrings [11,12,13,14,15] where the D-instanton effects match precisely with the predictions from
superstring dualities. In [16], worldsheet computations of instanton effects were performed in Calabi-
Yau orientifold compactifications, which is a new result and was not previously known from a dual
description.
Among all these successes, there is one particular observable that stands out and does not match with
the dual prediction. This is the annulus one-point amplitude in the original c“1string theory com-
putation of [2], which is relevant for computing the first subleading-in-gscorrection to the D-instanton
induced n-point amplitude of closed-string operators. This amplitude receives divergent contributions
from integration over the worldsheet moduli near the boundaries of moduli space. This leads to an
additive ambiguous term in the amplitude. Extracting the finite part of the worldsheet amplitude via
numerical integration over the moduli space, and comparing this with the amplitude from the dual
matrix quantum mechanics leads to a prediction for the ambiguous piece of the worldsheet amplitude
[2,17]. In [4], a string field theory analysis was performed to determine the ambiguous piece, but the
result was found to not match with [2,17], leading to a puzzle.
In the present work, we resolve this mismatch. We first simplify the model by working with the
că1non-critical string, and we study the integrated correlation functions of the cosmological constant
operator. The first simplification is that one does not have to worry about the translation zero mode
of the c“1scalar. Second, the one-point annulus amplitude of the cosmological operator has a
simple form that can be obtained by differentiating the partition function with respect to the world-
sheet cosmological constant µ. Third, because of the Liouville equation of motion, the cosmological
operator is a total derivative and the moduli space integral reduces to just boundary contributions,
obviating the need for numerical integration over the moduli space. In trying to compute the one-point
annulus amplitude in this simpler model, we were able to identify a subtle issue in the computation
in appendix D of [4], which analyzed the disk amplitude with one closed string puncture and three
open string punctures. This was needed for finding the relation between the string field theory gauge
transformation parameter and the rigid Up1qtransformation parameter under which an open string with
one end on the instanton picks up a phase.
Let us briefly explain the subtlety. The disk amplitude with one closed string puncture and three
open string punctures has a two-dimensional moduli space. String field theory instructs us to integrate
a two-form on a subset Sof this moduli space that excludes certain regions around the boundaries. The
two-form turns out to be exact. Let’s denote it by dJ, so that the moduli-space integral reduces to the
integral of Jover the boundary BSof S. It so happens that in appendix D of [4], when we go once
around BS, the open string punctures do not return to their original position, but to a configuration
related to the initial one by the one-parameter subgroup of PSLp2,Rqthat keeps the point z“iin
the upper half plane fixed. In such a situation, one must make sure that the contraction of Jwith the
tangent vector along the orbits of this PSLp2,Rqtransformation is zero, something that was not true
for the Jchosen in [4]. It turns that one can add an exact one-form to Jso that it satisfies the desired
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