Level truncation and the quartic tachyon coupling
Abstract
We discuss the convergence of level truncation in bosonic open string field theory. As a test case we consider the calculation of the quartic tachyon coupling
γ
4
. We determine the exact contribution from states up to level L=28 and discuss the
L→∞
extrapolation by means of the BST algorithm. We determine in a self-consistent way both the coupling and the exponent
ω
of the leading correction to
γ
4
at finite
L
that we assume to be
∼1/
L
ω
. The results are
γ
4
=−1.7422006(9)
and
|ω−1|≲
10
−4
.}