We present a new method, exact in ${\alpha }^{\prime }$, to explicitly compute string tree-level amplitudes involving one massive state and any number of massless ones. This construction relies on the so-called twisted heterotic string, which admits only gauge multiplets, a gravitational multiplet, and a single massive supermultiplet in its spectrum. In this simplified model, we determine the moduli-space integrand of all amplitudes with one massive state using Berends-Giele currents of the gauge multiplet. These integrands are then straightforwardly mapped to gravitational amplitudes in the twisted heterotic string and to the corresponding massive amplitudes of the conventional type-I and type-II superstrings.

中文翻译：

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通过场论方法散射大量弦共振

我们提出了一种新方法，准确地 ${\alpha }^{\prime }$，显式计算涉及一个有质量状态和任意数量无质量状态的字符串树级振幅。这种结构依赖于所谓的扭曲异质弦，它在其光谱中只允许规范多重峰、引力多重峰和单个大质量超多重峰。在这个简化的模型中，我们使用规范多重态的 Berends-Giele 电流确定具有一个质量状态的所有幅度的模空间被积函数。然后将这些被积函数直接映射到扭曲异质弦中的引力振幅以及相应的常规 I 型和 II 型超弦的巨大振幅。