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One-loop unitarity of string theories in a constant external background and their Seiberg-Witten limit

A. Bassetto·A. Torrielli·R. Valandro
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Abstract

Perturbative spectra and related factorization properties of one-loop open string amplitudes in the presence of a constant external background B are analysed in detail. While the pattern of the closed string spectrum, obtained after a careful study of the properly symmetrized amplitudes, turns out to be unaffected by the presence of B, a series of double open-string poles, which would be absent when B is turned off, can couple owing to a partial symmetry loss. These features are studied first in a bosonic setting and then generalized in the more satisfactory superstring context. When the background is of an ``electric'' type, a classical perturbative instability is produced beyond a critical value of the electric field. In the Seiberg-Witten limit this instability is the origin of the unphysical tachyonic cut occurring in the non-planar amplitudes of the corresponding noncommutative field theories.

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A. Bassetto, A. Torrielli, R. Valandro. 2003-11-26. One-loop unitarity of string theories in a constant external background and their Seiberg-Witten limit. https://doi.org/10.1088/1126-6708%2F2004%2F01%2F040

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