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arXiv · 2605.01784

A Non-local "Boundary'' Term for Two-Point Amplitudes in String Field Theory

Yasu Gen·Hiroaki Matsunaga·Jojiro Totsuka
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Abstract

We propose a new ``boundary'' term in free bosonic string field theory. Here, the term ``boundary'' refers to a contribution introduced to restore the cyclicity broken by the insertion of a stringy step-function operator, although it is not strictly localized as it involves an operator that selects positive-energy modes. We construct this term as a bilinear form involving the commutator of the BRST operator with the step-function operator. The resulting action has a well-defined variational principle. When evaluated on on-shell string fields, the proposed term reproduces the correct tree-level two-point amplitude for both open and closed strings. We verify this explicitly in the tachyon and massless sectors.

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Yasu Gen, Hiroaki Matsunaga, Jojiro Totsuka. 2026-05-03. A Non-local "Boundary'' Term for Two-Point Amplitudes in String Field Theory. https://arxiv.org/abs/2605.01784

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